final report revised for transcad 4 · 2011. 1. 26. · transcad 4.8 are comparable to that of...

CARTS TRAVEL DEMAND MODEL IMPROVEMENT PROGRAM (PHASE II) (S)METROPLAN. LITTLE ROCK ARKANSAS

MODEL VALIDATION

Final Report

Revised for TransCAD 4.8

Alliance Transportation Group, Inc.

In Association with

NuStatsURS Corporation

Bernardin • Lochmueller & Associates, Inc.Parsons Brinckerhoff Quade & Douglas, Inc.

Revised by Metroplan

100 East Anderson Lane Suite 300 Austin, Texas 78752 Phone 1.800.650.7869 FAX 512.821.2085

Revised by Metroplan in August of 2008

R e v i s e d M e t r o p l a n M o d e l V a l i d a t i o n – F i n a l R e p o r tM a y 2 0 0 8 P a g e - 2

THIS REPORT PRODUCED BY

ALLIANCE TRANSPORTATION GROUP, INC.

ORIGINAL DECEMBER 2004

REVISED BY METROPLAN MAY 2008


TABLE OF CONTENTS

Executive Summary/Model Overview 5

TransCAD 4.8 Upgrade 6

Results 7

Remaining Issues 10

Model Conversion to TransCAD 4.8 Format 11

Model Validation 11

Validation Criteria 12

Region-wide 12

Facility Type 14

Area Type 18

Screenline 20

Volume Range 24

Conclusion 25

Reference for validation section 26

Appendix A – ATG Technical Document on Model Conversion 27

Upgrade to 4.8 and Enhancements 27

Remaining Issues 30

Recommendations 38

Appendix B – Technical Memo on Revalidation 39

Delay Equation 39

TransCAD 4.7 Accuracy 41

Series 1 42

Series 2 45

Recommended Delay Equation Modifications 53

2030 Travel Demand Model Results 55

Appendix C – Screenline Roadways 57

Appendix D – Letter of Acceptance 60


LIST OF TABLES AND FIGURES

Table 1: Counted vs. Modeled VMT 13

Table 2: Modeled VMT Summary 13

Table 3: County Counted VMT vs. Modeled VMT 13

Table 4: County HPMS VMT vs. Modeled VMT 14

Table 5: CARTS Facility Types 14

Table 6: FHWA Facility Type Validation Targets 14

Table 7: Counted VMT vs. Modeled VMT by Facility Type 15

Table 8: CARTS Area Types 18

Table 9: Counted VMT vs. Modeled VMT by Area Type 19

Table 10: Suggested Validation Targets for Screenlines 20

Table 11: Counted vs. Modeled Volumes by Screenline 24

Table 12: MDOT Volume Range Validation Criteria 25

Table 13: Counted VMT vs. Modeled VMT by Volume Range Freeways 25

Table 14: Counted VMT vs. Modeled VMT by Volume Range Surface Streets 25

Figure 1: Travel Demand Model Accuracy for Freeways 16

Figure 2: Travel Demand Model Accuracy for Surface Streets 16

Figure 3: Graph of RMSE from TRB Report 288 for all Facility Types 17

Figure 4: Graph of RMSE from TRB Report 288 for Freeways 17

Figure 5: Graph of RMSE from TRB Report 288 for Major Arterials 18

Figure 6: CARTS Area Type Map 19

Figure 7: CARTS Screenlines 21

Figure 8: CARTS Screenlines (Central Inset) 22

Figure 9: Percent Deviation, NCHRP Guidelines 23


EXECUTIVE SUMMARY/MODEL OVERVIEW

Metroplan and AHTD use the Central Arkansas Regional Transportation Study (CARTS) Travel DemandModel to predict future traffic volumes and assess the impact of transportation projects within Faulkner,Lonoke, Pulaski, and Saline Counties. The CARTS Travel Demand Model is a standard four step modelincluding: Trip Generation, Trip Distribution, Mode Choice, and Traffic Assignment/Transit Assignment.The CARTS Model also utilizes a feedback loop of travel speed from traffic assignment to tripdistribution. Below is an illustration of the CARTS Model with a short description of each step.

CARTS Travel Demand Model

Land Use and Travel CharacteristicsModel inputs include socioeconomic data (population, households, school enrollment, and totalemployment) for traffic analysis zones and a roadway network to estimate the travel time between zones.Traffic projections are developed using forecasted land use and a future roadway network.

Trip GenerationTrip generation is the process by which trips are produced and attracted to travel analysis zones (TAZ). Atotal of 7 internal trip types (Home Based Work, Home Based School, Non Home Based – Work Related,Non Home Based – Other, Home Based Other 1, 2 & 3) are used. Trip generation is based on the landuse inputs and trip rates developed as part of travel surveys. The end result of trip generation is that forzone Y, X number of trips are produced and attracted for each trip type. External trips are treated as eitherexternal to external, external to internal work, external to internal other.

Trip Generation

Trip Distribution

Mode Choice

Traffic Assignment

FeedbackL

oop

Transit Assignment

Land Use and TravelCharacteristics

Emissions Post Processor


Trip DistributionThe second step of the model is trip distribution; this step involves the allocation of trips produced in theinitial step between all zones. The allocation is based on a gravity model that distributes trips based onthe travel time between zones and the number of trips attracted to a particular zone. The end result of tripdistribution is that X number of trips occurs between zones Y and Z.

Mode ChoiceMode choice is the step used to determine the approximate number of trips which will travel betweenzones by transit versus automobile. The end result of mode choice is that X% of trips between zones Yand Z will use transit rather than automobile.

Traffic AssignmentAutomobile trips are then assigned to the roadway network based on the shortest route (travel time)between zones. As the volume on a particular route begins to exceed its capacity the travel speed isreduced and new trips are assigned to parallel routes. The end result of traffic assignment is the forecastAverage Daily Traffic (ADT) for a particular roadway. Traffic volumes are reported for the entire daywith no time of day information.

Emissions Post ProcessorMetroplan maintains an emissions post processor which can be used to estimate daily emissions of VOC’sand NOx. The post processor takes the daily volumes from traffic assignment, dividing them into hourlyvolumes and estimated Hourly VMT and travel speeds. This data is then input into Mobile 6 to developemission rates and the calculation of daily travel emissions. The post processor has not been calibratedfor all local data; therefore it is used only for sensitivity analysis. If the Central Arkansas area is declarednon-attainment for ground-level ozone, the emissions analysis will be refined based on discussionsbetween Metroplan, AHTD, FHWA, ADEQ, CATA, FTA, and EPA and fully calibrated to local data.

Transit AssignmentTransit trips are assigned to bus routes using travel time, bus headways, transit fares, and number oftransfers required. The end result from transit assignment is the forecast number of individuals riding abus route. Estimated ridership is provided for both Peak and Off-peak travel times.

TRANSCAD 4.8 UPGRADE

The CARTS Travel Demand Model was originally created for use with TransCAD 4.7 in 2004.Metroplan sought to update the CARTS Model in 2007 so that it could be run on the new softwareversion, TransCAD 4.8. Alliance Transportation Group and Caliper assisted Metroplan with the updateof the CARTS Model for TransCAD 4.8. This process involved updating the model scripts to reflectnewly added and modified functions within TransCAD leading to a need to recalibrate the delay equationused during traffic assignment and revalidation the model. Recalibration and revalidation is described indetail as part of this report in the following section.


RESULTS

With minor modifications to the delay equation used in the CARTS Model, the results produced inTransCAD 4.8 are comparable to that of TransCAD 4.7 (see appendix B). The results from TransCAD4.8 also meet the validation criteria original set forth for the CARTS Model which is based on guidelinesused by most MPO’s within the Country. A more detailed review of validation begins on page 11 of thereport. Figures E1 and E2 show the accuracy of the CARTS Model for base year model runs inTransCAD 4.8 for freeways and surface streets and that the majority of counts meet the acceptable rangeof deviation set forth in National Cooperative Highway Research Project (NCHRP) Report 255.

Figure E1: Travel Demand Model Accuracy for Freeways


Figure E2: Travel Demand Model Accuracy for Surface Streets

Delay Equation

The CARTS Model used the Logit-delay function within TransCAD to assign link delay. Table E1 listedthe default coefficients, as well as those calibrated for the CARTS Model in TransCAD 4.7 and 4.8.Figure E3 illustrates the effects of congestion on travel speed within the CARTS Model delay equationwith comparisons to the Bureau of Public Road (BPR) Delay Curve. The revised equation results inslightly higher speeds for a given volume to capacity ratio, and more closely resembles that of the BPRCurve calibrated to the Highway Capacity Manual. The Logit-delay function results in speed calculationslower than the BPR Curve at volume to capacity ratios less than 1 and speeds higher than the BPR Curveat volume to capacity ratios greater than 1.

Table E1: CARTS Model Delay Equation

Freeways Arterials

C1 C2 C3 C3 Peak C4 C1 C2 C3C3

Peak C4

Default Values 0.9526 1 3 3 0.9526 1 3 3

TransCAD 4.7 0.9526 1 2.5 2 3 0.9526 1 3 2.5 3

TransCAD 4.8 0.9526 1 3 2.5 3 0.9701 1 3.5 3 3

*TransCAD 4.8 based on Scenario 2a, see appendix B


Figure E3: Calibrated CARTS Model Delay Equation

R e v i s e d M e t r o p l a n M o d e l V a l i d a t i o n – F i n a l R e p o r tM a y 2 0 0 8 P a g e - 1 0

REMAINING ISSUES

The CARTS Travel Demand Model has been recalibrated and revalidated and is ready for use withTransCAD 4.8. With all travel demand models there is a constant desire to refine the model and improvethe overall accuracy and predictability of the model. As the model is applied in the planning processthese modifications are often made as part of individual projects. As additional years of socioeconomicdata and traffic counts become available additional refinements to the model can be made, including areview of the delay equations and its performance at higher V/C ratios. The next major update of themodel should include a review of ramp volumes, one-way frontage road capacities and speeds, and apossible refinement of external trip distribution for freeway stations. Time of day modeling and re-evaluating the adequacy of the model choice model for modeling higher end transit projects may also bedesired to improve scenario testing and the development of hourly volumes for emissions and operationalanalysis.


MODEL CONVERSION TO TRANSCAD 4.8 FORMAT

Alliance Transportation Group, with the assistance of Caliper Incorporated, updated scripts for theCARTS Model so that it could be run on TransCAD 4.8. The changes to the CARTS Model scripts aredocumented in memorandum WA#1, Appendix A, from Alliance Transportation group dated January 29,2008. Following delivery of the CARTS Model update, Metroplan sought to revalidate the model andreview the delay equation as the script and version changes resulted in a VMT drop of 5%.

The CARTS Travel Demand Model results from TransCAD 4.8 were initially reviewed and found to havelead to an undesired reduction in VMT and overall accuracy of the CARTS Model. After reviewing theoutput file from TransCAD versions 4.7 and 4.8, it was determined that it would be necessary to reviewthe delay equation and make modifications in TransCAD 4.8 to improve the overall accuracy and forecastof the model. Appendix B contains a memo describing the process of reviewing the delay equation andsubsequent model runs.

The remaining sections of the report reflect the updated model scripts and modification to C3 (Freeways3.0 and other facility types 3.5). It should be noted that a similar format to that of the original validationreport being used, but several additional figures and tables have been added or modified. Root MeanSquare Error (RMSE) was calculated on link VMT in the original validation report; in this RMSE iscalculated for counts (more common).

Due to earlier modifications to the model and the removal of unnecessary nodes, slight differences occurbetween versions 4.7 and 4.8. Traffic counts used to validate the model in TransCAD 4.8 include 2000base year counts as well as the CARTS ADT database. Counts have been added or modified where a2000 count was missing, was abnormally high or low compared to subsequent years, or where countsstarted in 2001 and a reasonable assumption could be made to the traffic count for 2000.

MODEL VALIDATION

The ability of travel demand models to forecast future year traffic and other travel behavior are predicatedon their ability to estimate “known” traffic volumes and travel patterns under base year conditions forwhich extensive data is available. There are two components to the process of matching model results tothe observed base year travel data. These components are calibration and validation.

Calibration refers to the process of estimating model variables such as trip rates, friction factors, mean triplength, and trip length frequency distributions. All variables are ideally based on surveyed or observeddata. The CARTS model is based on observed data collected during the various survey effortsaccomplished in support of this model, and available network information (including counts).

Validation refers to the process of using a calibrated model to estimate travel assignments for the baseyear and comparing these travel assignments to observed travel data. The typical comparison, whensufficient data is available, is between highway traffic assignments and actual traffic volumes derivedfrom traffic count data. Extensive traffic counts must be available to validate a model.

Validation of the model to counted traffic flows is important to the model effort in two areas. First, itshows if the calibration tools used in the model process and assumptions were reasonable. Second, thevalidation shows what level of confidence the user can have in the forecast results.


VALIDATION CRITERIA

Although the principle of comparing traffic assignments to traffic count data is intuitively straightforward,subjective review of the travel demand model results and the observed traffic counts is not adequate. Thecomparative analysis must be carried out in a structured manner using clearly defined benchmarks ormeasures of success that allow the results of the validation analysis to be tabulated, and quantitativelyanalyzed in a way that provides the user with a degree of confidence in the statistical foundation andstructure of the model.

The model validation procedure for the CARTS Model is similar to the procedure used MPOs throughoutthe country. The locations of year 2000 traffic counts provided by Metroplan have been coded to theCARTS roadway network and the counts themselves were added to the base year network attributes.Traffic assignment results for the validation year (2000) will be compared to these traffic counts tocalculate a percent error value that will be aggregated and tabulated across a variety of categories. Thesecategories are listed below and discussed individually in the following sections:

• Region-wide• Facility Type• Area Type• Screenlines• Volume range.

REGION-WIDE

The first step in the validation process is to analyze overall vehicle miles of travel (VMT). BecauseMetroplan has more confidence in the VMT derived from traffic counts than that derived from theHighway Performance Monitoring System (HPMS) data, more emphasis was placed on the count-derivedestimates.

The two VMT estimates, HPMS and count based, are derived using different methodologies and interpretthe data at slightly different scales within the study area. The result of these variations is that the twosources of “observed” data are themselves different, making it impossible to match both values.

Both data sources are, however, valuable in both validation and transportation analysis. Therefore, theproposed goal under this criteria is to match the more direct values of VMT provided by the aggregationof the link based count data, but to also check for reasonableness against the overall HPMS numbers byfacility type.

As stated earlier, the main validation criterion is the match between counted and modeled VMT. TheCARTS model is able to accurately reproduce roadway flows within 2%, on an aggregate basis, of thetotal VMT based on counts. The percent of VMT produced by the model versus total VMT based oncounts is 101.86%. The table below depicts the VMT produced by the model and by the counts andprovides a statistical comparison to demonstrate the quality of the match.


Table 1: Counted vs. Modeled VMT

Total Counted VMT On Counted Links 7,566,572Total Modeled VMT On Counted Links 7,707,136Links with Counts 1116% Root Mean Square Error 27.51%Percent Modeled VMT Of Counted VMT 101.86%

Overall modeled VMT and the portion that appears on counted links are also of interest and are presentedin the following table. The CARTS network has count coverage to represent nearly 40% of the totalsystem VMT. This indicates that a significant number of links contain data that can be used to compareobserved data to modeled data.

Table 2: Modeled VMT Summary

Total Modeled VMT On All Links 19,345,860Total Modeled VMT On Functional Classified Links (No Centroid Connectors) 18,062,535Total Modeled VMT On Counted Links 7,707,136Percent Of Modeled VMT On Counted Links 39.84 %Percent Of Modeled VMT On Counted Links (no Centroid Connectors) 42.67%

It is also necessary to validate the travel demand models by sub-region or district. This analysis isperformed using counties as the sub-regions for the CARTS model. The following table comparesmodeled VMT to counted VMT and HPMS estimated VMT at the county level. Each of the Countiesmodeled versus count based VMT fall within the 1 to 3.5% range. This indicates that the model isperforming uniformly well across large, diverse geographic areas.

Table 3: County Counted VMT vs. Modeled VMT

County% of

CountCounted

VMTModeled

VMT*Faulkner (1) 103.35% 570,590 589,700Lonoke (2) 101.18% 1,107,973 1,121,006Pulaski (3) 101.54% 4,980,553 5,057,180Saline (4) 103.04% 907,456 939,250Total 101.86% 7,566,576 7,707,136

*Modeled VMT is on links with a count.

The following table compares modeled VMT and HPMS estimated VMT at the county level. The HPMSestimate of VMT is slightly lower than that estimated by the model. Still modeled VMT is clearly similarto the HPMS estimates for each county. Again because of difference between the VMT estimated fromcounts and the HPMS estimates only one could be used as a validation target. MetroPlan felt that theVMT estimated directly from the 2000 counts was better and used these for validation purposes. For theentire 4 county area, the model estimates VMT at 113% of HPMS data. For individual counties theestimates range from 107% for Pulaski County to 135% for Saline County.


Table 4: County HPMS VMT vs. Modeled VMT

COUNTY % OFCOUNT

HPMSESTIMATED

VMT

MODELEDVMT

Faulkner (1) 115.08% 2,318,489 2,668,200Lonoke (2) 121.25% 1,923,367 2,332,087Pulaski (3) 106.85% 10,889,467 11,635,082Saline (4) 134.43% 1,931,533 2,596,493Total 113.38% 17,062,856 19,345,860

FACILITY TYPE

Another criterion for model validation is to compare assigned traffic volumes to traffic counts aggregatedby facility type. The following facility types are used in the CARTS model.

Table 5: CARTS Facility Types

FACILITY TYPE FACILITY TYPENUMBER

Centroid Connector 0Freeway 1Major Arterial 2Minor Arterial 3Major Collector 4Frontage Road 5Ramp 6HOV 7HOV Ramp 8

It is important to note that only freeways, major arterials, minor arterials, and major collectors havecounts to which comparisons can be made. There are currently no HOV or HOV ramp facilities in theCARTS network. The comparison of assigned volumes to counted volumes is considered successful ifthe value for percent error falls within the ranges suggested by the FHWA depicted below.

Table 6: FHWA Facility Type Validation Targets

FACILITY TYPE FHWA TARGETSFreeway +/- 7%Major Arterial 10%Minor Arterial 15%Collector 25%


The following table shows the comparison of the modeled verses the counted links by facility type.Metroplan recommended a 10% desirable percent deviation for volumes over 25,000 and 15% desirablepercent deviation for volumes under 25,000. Note that all the freeways are coded directionally with eachside of the freeway and each set of frontage roads represented independently by separate links. Counts onthe freeways were divided by two to estimate the one-way counts on the freeways from the two-waycounts provided by Metroplan. In the validation statistics the freeway category is made up of one-waylinks that are within 5% of the traffic counts overall. The following table shows that the model ismatching counts by facility type within the FHWA Facility Type Validation Targets.

Table 7: Counted VMT vs. Modeled VMT by Facility Type

FACILITYTYPE

LINKSWITH

COUNTCOUNTED

VMTMODELED

VMT

% OFCOUNT

VMT

SUM OFCOUNTS

SUM OFMODEL

ESTIMATE

% OFCOUNT

% ROOTMEAN

SQUARED

Freeway 196 5,120,713 5,118,145 99.95% 5,787,300 5,877,904 101.57% 13.85%MajorArterial 400 1,560,297 1,592,350 102.05% 4,666,000 4,481,359 96.04% 30.34%MinorArterial 339 716,971 802,790 111.97% 2,125,660 2,147,350 101.02% 41.10%MajorCollector 173 160,536 184,369 114.85% 614,750 669,551 108.91% 70.20%All 1116 7,566,572 7,707,136 101.86% 13,235,160 13,228,827 99.95% 27.26%

Figures 1 and 2 show the accuracy of the CARTS Model in reproducing traffic counts for freeways andsurface streets (Major Arterial, Minor Arterial, and Major Collector) compared to the traffic count. Anaccuracy of 1 indicates that the model is reproducing the traffic count exactly; an accuracy of .8 indicates themodel is reproducing volumes at 80% of the traffic count where an accuracy of 1.2 indicates the model isreproducing volumes at 120% of the traffic count. NCHRP 255 recommendations for maximum deviationsfor screenlines is shown on the figures, adjustments were made to the freeways to reflect one-way counts.

The majority of traffic counts for freeways are reproduced at 80% to 120% of the actual count (80%). Thelinear trend of these counts versus accuracy shows a line slightly above 1, the average and median of thesecounts is 102%. The accuracy of the model for arterials and collectors is greatly improved at higher volumes,which is common with most models which tend to be less accurate at very small volumes. A moving averagemethod shows that on average the model estimates volumes at 137% of the actual volumes at 5000 ADT,100% at 10,000 ADT, before leveling off between 90% and 95% at higher volumes. At higher volume thecapacity of the facility is exceeded and traffic is diverted to parallel routes.


Figure 1: Travel Demand Model Accuracy for Freeways

Figure 2: Travel Demand Model Accuracy for Surface Streets


The CARTS Model was compared to that of other metropolitan regions using Transportation ResearchBoard’s Study 288, Metropolitan Travel Forecasting – Current Practice and Future Direction. The CARTSModel overall RMSE of 26.26% is slightly better than the mean value of 30% from the study. The CARTSModel RMSE of 13.85% for freeways is better than most models whose mean value is 19%. The CARTSModel RMSE of 30.34% for major arterials is also comparable with other travel demand models whose meanvalue is approximatly 30%. CARTS Model Results are shown in red.

Figure 3: Graph of RMSE from TRB Report 288 for all Facility Types

Figure 4: Graph of RMSE from TRB Report 288 for Freeways


Figure 5: Graph of RMSE from TRB Report 288 for Major Arterials

AREA TYPE

The following shows the comparison between assigned and counted volumes by area type. The target forthis criterion is for the aggregate modeled volume to be within 15% of the aggregate observed volume foreach area type. The following area types were used for the CARTS model.

Table 8: CARTS Area Types

Area Types Area Type NumberCBD 1Urban 2Suburban 3Rural 4


Figure 6: CARTS Area Type Map

An estimate of both VMT and counts was completed for each area type. The comparison betweencounted and modeled VMT by area type is within FHWA validation criterion for all area types. Themodel results are best for Urban and Suburban area types and least accurate for rural areas.

Table 9: Counted VMT vs. Modeled VMT by Area Type

FACILITYTYPE

LINKSWITH

COUNTCOUNTED

VMTMODELED

VMT

% OFCOUNT

VMT

SUM OFCOUNTS

SUM OFMODEL

ESTIMATE

% OFCOUNT

% ROOTMEAN

SQUARED

CBD 24 19,379 22,042 113.74% 202,560 202,950 100.19% 47.29%Urban 433 2,209,513 2,172,819 98.34% 7,681,510 7,504,073 97.69% 21.98%Suburban 396 3,559,202 3,510,976 98.65% 4,157,900 4,060,886 97.67% 28.57%Rural 263 1,778,477 2,001,298 112.53% 1,193,190 1,460,918 122.44% 46.49%


SCREENLINE

Screenlines are a set of selected traffic count locations that stretch across a travel corridor or market shedalong a physical or imagined boundary. The aggregate volumes across the screenline provide acomprehensive snapshot of travel demand in the selected corridor. Based on NCHRP 255 guidance, thetarget for acceptable screenline comparisons follow the criteria listed in the following table.

Table 10: Suggested Validation Targets for Screenlines

Total Screenline 24-Hour Traffic Count

Percent Deviation

25,000 +/- 43%50,000 33%75,000 29%100,000 25%125,000 21%150,000 20%175,000 19%200,000 18%

Source: NCRHP 255 P. 49 (Cited in FHWA, Calibration andAdjustment of System Planning Models, Dec. 1990 and Travel ModelImprovement Program, Model validation and ReasonablenessChecking Manual, June 2001)

The 34 screenlines defined as part of the CARTS model validation are displayed in the figures below.Note that screenlines must be defined where counts are available for all the links crossed.


Figure 7: CARTS Screenlines


Figure 8: CARTS Screenlines (Central Inset)


Figure 9: Percent Deviation, NCHRP Guidelines

As presented in the chart above and with more detail in the table below, 31 of the 32 screenlines matchwithin the suggested validation criteria presented earlier. The most obvious location for a screenline andone that is an important measure of the validation is the river. To have a screenline at the river counts onI-30 were estimated from the counts on either side of the river and ramp volumes. The river screenline,screenline 1, compares well at 111.69% of the counted volume. This screenline is particularly useful indisplaying that the correct number of trips are crossing the river since the arterial bridges downtown arehigh while I-30 is slightly low. The one screenline that exceeds the suggested threshold is screenline 27(Chester, State, Broadway) which is slightly larger than the suggested error, primarily due to an overestimation of the Broadway Bridge.


Table 11: Counted vs. Modeled Volumes by Screenline

ScreenLine Percentof Total

AbsolutePercent

Error

Counted Modeled

1 111.69% 11.69% 222,000 247,9492 112.60% 12.60% 118,500 133,4373 95.91% 4.09% 57,500 55,1494 104.50% 4.50% 95,700 100,0055 119.51% 19.51% 23,000 27,4886 124.58% 24.58% 14,870 18,5267 104.59% 4.59% 34,400 35,9798 139.28% 39.28% 22,610 31,4919 116.95% 16.95% 51,700 60,464

10 103.09% 3.09% 183,800 189,47911 88.57% 11.42% 58,900 52,16912 112.16% 12.16% 135,000 151,41213 100.03% .03% 67,300 67,32114 111.35% 11.35% 70,600 78,61215 90.06% 9.94% 57,000 51,33316 92.67% 7.33% 86,300 79,97817 89.47% 10.53% 71,600 64,06118 84.85% 15.15% 31,500 26,72919 115.52% 15.52% 47,200 54,52720 99.80% .20% 32,900 32,83721 101.80% 1.80% 41,300 42,04222 102.02% 2.02% 56,300 57,43523 98.02% 1.98% 118,000 115,65924 130.47% 30.47% 58,500 76,32725 117.71% 17.71% 10,000 11,7712627 142.46% 42.46% 31,800 45,3012829 128.81% 28.81% 21,090 27,16730 119.03% 19.03% 3,810 4,53531 101.90% 1.90% 22,000 22,41832 96.66% 3.34% 12,400 11,98633 107.69% 7.69% 148,300 159,71034 108.37% 8.37% 114,000 123,537

VOLUME RANGE

The final validation criterion is to compare observed verses modeled volumes within acceptable volumeranges. This section documents them as meeting the suggested targets used by the Michigan Departmentof Transportation (MDOT) depicted below. The MDOT values were selected due to the stringencyassociated with the more statistically significant facilities carrying volumes above 5,000. While otherapproaches emphasize the importance of the lower volume facilities, the MDOT approach places a highervalue on matching the statistically significant higher volume facilities.

Percent deviation = (Base Year Assignment – Base Year count) / Base Year Count


Table 12: MDOT Volume Range Validation Criteria

AVERAGE ANNUALDAILY TRAFFIC

DESIRABLE PERCENTDEVIATION

< 1,000 200%1,000 –2,500 100%2,500-5,000 50%5,000-10,000 25%10,000-25,000 20%25,000-50,000 15%>50,000 10%

Based on FHWA 1990 "Calibration and Adjustment of System PlanningModels" as documented in Model Validation and ReasonablenessChecking Manual, June 2001, Travel Model Improvement Program.

The CARTS model validation meets the criteria for each volume range shown above. Tables 13 and 14below provides more detail and comparison statistics for freeways and surface streets at different volumelevels.

Table 13: Counted VMT vs. Modeled VMT by Volume Range Freeways

AVERAGEANNUAL

DAILYTRAFFIC

LINKSWITH

COUNTCOUNTED

VMTMODELED

VMT

% OFCOUNT

VMT

SUM OFCOUNTS

SUM OFMODEL

ESTIMATE

% OFCOUNT % ROOT

MEANSQUARED

<50,000 77 2,350,420 2,352,107 100.1% 1,381,300 1,367,168 99.0% 20.7%>50,000 119 2,770,293 2,766,037 99.8% 4,510,736 4,406,000 97.7% 11.7%

Table 14: Counted VMT vs. Modeled VMT by Volume Range Surface Streets

AVERAGEANNUAL DAILY

TRAFFIC

LINKSWITH

COUNTCOUNTED

VMTMODELED

VMT

% OFCOUNT

VMT

SUM OFCOUNTS

SUM OFMODEL

ESTIMATE

% OFCOUNT

% ROOTMEAN

SQUARED

<1,000 87 58,337 102,905 176.4% 53,910 111,589 207.0% 233.4%1000-2,500 151 167,325 293,785 175.6% 259,400 445,275 171.7% 125.1%2,500-5,000 178 338,755 441,374 130.0% 650,200 862,535 132.7% 69.2%5,000-10,000 214 592,582 599,439 101.2% 1,484,900 1,467,823 98.8% 37.6%>=10,000 282 1,280,803 1,142,004 89.2% 4,958,000 4,411,038 89.0% 23.7%

CONCLUSION

The criteria proposed for the CARTS travel demand model validation process are based on currentFHWA and NCHRP guidance and standards and represent reasonable measures for determining theaccuracy and reliability of the CARTS model. The validation of the CARTS model described in thissection accomplishes two goals. First, it demonstrates that the calibration tools used in the model processand assumptions were reasonable. Second, the validation provides Metroplan with a high level ofconfidence in the accuracy and reliability of forecast results obtained from the CARTS travel demandmodel. After conversion of the Model to TransCAD 4.8, the CARTS Model reproduces volumes at orbetter than the standards for travel demand models and comparable to that from TransCAD 4.7.Appendix D contains the letter of acceptance from both Metroplan and AHTD.


REFERENCE FOR VALIDATION SECTION

Model Validation and Reasonableness Checking Manual, June 2001, Travel Model ImprovementProgram, U.S. Department of Transportation, Federal Highway Administration.

National Cooperative Highway Research Program, Report 365, Travel Estimation Techniques for UrbanPlanning, 1998, Transportation Research Board (TRB).

National Cooperative Highway Research Program, Report 255, Highway Traffic data for Urbanized AreaProject and Design, 1995, Transportation Research Board (TRB).


APPENDIX A – ATG TECHNICAL DOCUMENT ON MODEL CONVERSION

MemorandumTo: Casey Covington, Metroplan

From: Mike Chaney, Alliance Transportation Group

CC: Jim Harvey, Alliance Transportation Group

Date: January 29, 2008

Re: Metroplan on call professional services WA#1

The purpose of this memorandum is to summarize the work preformed by Alliance Transportation Group,Inc. (Alliance) under work authorization #1. Alliance was contracted to perform the following the updatesand enhancements;

1. Upgrade the model to run in TransCAD 4.8a. Identify and correct problems associated with running the CARTS travel demand

model in TransCAD 4.8.b. Test and document in a brief tech memo the status of the highway and transit

models.c. Package all changes to the model components (with highway network and transit

route system) as a self-installing executable.2. Automate the selection of the walk access input file prior to each run of a new year.

This memorandum is composed of several sections describing the work listed above. The first sectiondescribes the specific upgrades and/or enhancements required to achieve the consistent execution of themodel in TransCAD version 4.8. The second section describes additional steps that could be taken to enhancemodel performance in the modified environment.

We at Alliance have enjoyed working with you on this project, and look forward to working with you again inthe future. If you have any questions or need any further information, please let me know.

UPGRADE TO 4.8 AND ENHANCEMENTSThe CARTS travel demand model was developed in TransCAD version 4.7. With the subsequent release ofTransCAD version 4.8, after allowing time for the software to mature in the marketplace, the CARTS staffdesired to migrate the CARTS model to the new TransCAD version. This upgrade proved to be less thanstraightforward and CARTS staff requested assistance from Caliper Corporation. Even with several months ofsignificant levels of vendor support from Caliper, only limited success was achieved in making the upgrade toversion 4.8.

At this point, CARTS contracted with Alliance Transportation Group, Inc., which had been serving as aliaison between CARTS and Caliper, to complete the upgrade. This work was undertaken as workauthorization #1 to the Alliance on-call contract with CARTS. This section describes the specific upgradesand enhancements made to the CARTS model set required for the CARTS model to run in TransCAD 4.8.


The majority of the changes in functions, protocols and procedures between TransCAD version 4.7 andversion 4.8 were in the transit component of the model. The transit component of the mode choice model isalso the unit of the model where most of the conversion problems experienced by CARTS and Caliper hadoccurred. For this reason, the primary Alliance work effort under this work authorization focused on updateand modification of the mode choice macro in order to adapt the resource code to be compatible with and takeadvantage of new or revised TransCAD functions. Because it applies many of the same functions, the transitassignment macro also required many of these same changes.

Walk Access ProportionTo minimize the manual steps required to apply the CARTS model, the selection of the walk accessproportion file was automated. The file name is now displayed on the model setup interface. The interfaceautomatically selects the default file for the specific year entered in the model setup tab of the interface. Thewalk access proportion file can also be selected from the model setup interface. If an alternative scenario isrun the interface should be used to select the run specific walk access proportion file.

The file name and location of the walk access proportion files have changed. The file name now contains themodel run year and the files reside in the C:\CARTSModel\MC directory. There are separate folders namedEnhanced and Express for the enhanced and express scenario files. The 2030 walk access proportion filenames for these two scenarios contain “ENH” for enhanced or “EXP” for express.

The modified model setup interface is depicted below in figure 1.

Figure 10, Model Interface


Travel TimesIn TransCAD version 4.7 drive links and walk links had to be mutually exclusive. In TransCAD 4.8 a link canbe both a walk link and a drive link. This represents an improvement that allows the user to more accuratelydepict the way the transportation system operates, but it also requires different treatment by the user indefining the walk and drive selection sets. For this reason the transit assignment and mode choice macroswould not run in version 4.8 until the travel times stored on the highway network were populated differently.The macros required that the unused direction of one-way links be populated with the travel time from theused direction. The macros will not run with a null, zero in these fields. More specifically, the travel timefield modified is *_CurrHWoptime (AB_CurrHWoptime and BA_CurrHWoptime). This procedure isperformed with the highway assignment macro.

Null values in these fields could cause problems for mode choice in the following two instances.1. A transit route traverses a link in the opposite direction of the link flow direction. For

instance, if you have a link with Dir = 1 and hence this link has a time value specified in theAB direction and null in the BA direction. A transit route should not traverse the link in theBA direction.

2. If you have a separate walk time or non-transit time for the AB and BA sides of the link andone of these fields has a missing value.

Drive SetOne significant change between TransCAD 4.7 and 4.8 relates to utilization of the drive-access path-buildingsetup options. In the original model under 4.7, the drive-access options were activated in the “TransitNetwork Setting” function. In Version 4.8, these options are now incorporated into the “Build TransitNetwork” function. At Caliper’s suggestion, Alliance modified the mode choice model macro so that driveaccess links are now created using new features controlled by the “Drive Set” and “Drive Links” optionswithin “Build Transit Network” function. The changes as implemented resolved a variety of modelapplication failures experienced in this component when running in 4.8, however, full analysis andinterpretation of why the changes are effective is not possible because Caliper has not yet documented thesenew Version 4.8 functions. The specific lines of code modified and the functions involved are listed below:

• Line added to “Build Transit Network”o Opts.Input.[Drive Set] = {highway_db+"|"+link_lyr, link_lyr, ntr_dr_set,

ntr_dr_qry}• Line removed from “Transit Network Setting SP”

o Opts.Input.[Driving Link Set] = {db_link_lyr, link_lyr, ntr_dr_set, ntr_dr_qry}

This change was required in both the mode choice and transit assignment macros.

Transit Travel TimesCaliper added centroid connectors as a facility type to the procedure that calculates transit travel time.Specifically, they reformatted the array structure of two functions that store factors developed by facility typeand used in the calculation of transit travel times.

See lines 500 to 580 of the resource code MODECHOICE.RSC.

Alliance added a facility type seven (FT_7) field to files OpFactor.dbf and PkFactor.dbf to match the arraystructure modified by Caliper. The field is used to calculate the travel time on centroid connectors. This


change is required to work with changes that Caliper made to the mode choice macro. Caliper likely madethe same change but did not provide the companion dbf files.

Route SystemThe model interface was revised to automate the tedious task of associating the transit route system to thehighway network. The CARTS model will now automatically associate the selected route system with theselected network each time the network layer and route system are selected with the layer tool on the modelinterface. This change makes it slightly easier for the user to apply the model by eliminating the requirementfor manual execution of a GISDK command.

Model InterfaceThe model will no longer open multiple instances of the CARTS Model menu. This change will prevent theuser from inadvertently running the model with the wrong parameters, thus reducing the potential for error orconfusion during multiple model runs.

Park and Ride LayerTo facilitate analysis of alternate scenarios, the park and ride layer is now year specific. A park and ride layerwith a name in the following format is required for each year.

C:\CARTSModel\GeoFiles\Network\PNR Layer\CARTSPNRlinks_00.dbd

We did not delete the unused facilities from any of the layers, but did create copies of the original layer andname them appropriately. This was an early attempt to get the model to run in version 4.8. While the changedid not help in that regard there are benefits to separate layers and therefore the change was retained. Theseparate layers can be edited to reflect the desired configuration for each analysis year.

Trip Length ReportingThe ability to report the resulting trip length by trip purpose and model iteration was developed for validatingthe original CARTS model. The feature was disabled in the final deliverable. Alliance enabled the featurefor this work effort. MetroPlan chose the option of keeping the feature enabled.

REMAINING ISSUES

TransCAD 4.8 buildsDuring the current work, problems inherent to some of the new builds in which TransCAD Version 4.8 wasnot performing as documented were identified and reported to Caliper. Caliper responded with fixes in theform of newly refined builds that addressed the problem. However, the fixes themselves also occasionally hadproblems that have not necessarily been resolved.

The final testing and bench marking of the CARTS model were done with build 500. The CARTS modelshould only by run in build 500 of the TransCAD software. This limitation is because Version 4.8 displays abroader range of variability across build numbers in terms of the function set available and how the availablefunctions are applied. For example Build 545 fails to support a procedure available in all previous buildscalled “cell-by-cell” to add matrix cores together. Since this procedure is used extensively in the CARTS


model code, Build 545 does not correctly combine the matrix cores during execution of the CARTS model.Caliper attempted to correct this oversight in Build 560 but the repair resulted in another as yet unknown issueand the model produces only 4,000,000 in VMT although the model runs to completion and no error messageis received.

VMT

The upgraded CARTS model produces around 5% less vehicles miles traveled (VMT) than the originalversion of the model. This effect is consistent in all model years.

Alliance thoroughly examined each adjustment made in the mode choice model to determine if the differencein VMT was due to these adjustments. Special attention was given to the required changes related to the traveltime field described previously in this document, which seemed a likely source of the change. To test theimpact of this change, considerable effort was expended to run the 4.7 version of the model with and withoutthe piece of code that updates the travel times. No difference was observed. Note that it is not possible to testthe 4.8 version in this manner because the mode choice model will not run without filling the travel timesfields on the unused side of one-way links.Based on tests of the primary changes to the CARTS macros without significant impact on VMT lead us tobelieve that the difference in VMT results observed between Version 4.7 and 4.8 are the result of changes inthe way the TransCAD native functions are applied within the two versions. Version 4.8 is the first version ofTransCAD to support multiple processors. This change alone would have required Caliper to “touch” manynumerical calculations in the software to provide multiple threading capability. Documentation on thesechanges has not been circulated to users, presumably because they affected only proprietary internal softwarecode without affecting the look or feel of user accessible code or functions. Full analysis of the source of thedifferences is not possible for two reasons.

1. As of this writing, Caliper has not yet documented all of the changes in functions, and;2. Direct testing of most of the changes to the mode choice model is not possible in Version 4.7

because TransCAD Version 4.8 is not backwardly compatible.

Caliper designed Version 4.8 with several components (e.g. Transit route system and several new orredesigned functions) that are not backwardly compatible to Version 4.7. Therefore the changes requiredto make the model run in 4.8 preclude it from working in 4.7. Because the changes are required forexecution in 4.8 all that can be deduced is that there is a difference. Both MetroPlan and Alliance havebenchmarked the two version of the model. From this it is clear that the difference in VMT is small afterthe first iteration of the model and increases when feedback is incorporated. The issue is not believed tobe the feedback process itself. The only change to the feedback process is the modification discussed inthe Travel Time Section above. The VMT differences between versions 4.7 and 4.8 are depicted in thetwo charts below.

Table 15, Year 2000 VMT

2000 Passenger Vehicle VMT

2000 Truck VMT

Total 2000 VMT

Number of Itterations

TransCAD 4.7 17,325,719 2,487,571 19,813,290 4TransCAD 4.8 build 500 16,293,654 2,485,189 18,778,843 4Difference -5.96% -0.10% -5.22% 0


Table 2, Year 2030 VMT

Total 2030 VMTNumber of Itterations

TransCAD 4.7 29,408,700 4TransCAD 4.8 build 500 27,729,844 5Difference -5.71% -1

*4.7 VMT from Metroplan

The VMT difference was not entirely unexpected. On recent projects in the Dallas Fort Worth and BatonRouge areas which were begun with 4.7, but finished with 4.8, our project teaming partners noted that theresults they obtained with the two versions were typically different by some small degree and adjustment tothe models were applied during the course of the project.

During deliberations on upgrading to 4.8 for a project in the Dallas area, the modeling director at theNCTCOG noted, after discussions with Caliper, that the Version 4.8 approach to implementing thegeneralized cost function (the function used in the CARTS model to apply the equilibrium assignmentimpedances) had been upgraded and was more robust than previous versions. Despite the improvement, betteris still different, NCTCOG had to address changes to the way they handled their volume delay functions tomake a successful switch to 4.8.

The model for Baton Rouge, LA required some adjustments to the code during the transition from version 4.7to version 4.8 including the same travel time fix for one-way links applied in the CARTS model. This changewas necessary even thought the mode choice code in the Baton Rouge model bears little resemblance to theCARTS model and relies more directly on TransCAD functions as opposed to customized code. Althoughthe Baton Rouge model has a feedback loop using the same convergence procedure as the CARTS model, wecannot determine if a similar VMT drop was experience because the base year Baton Rouge model was notyet validated in version 4.7 when the switch to version 4.8 was made, and the validation process wasperformed by a project teaming partner.

In our experience most model that switch software platforms or institute a major upgrade of the same softwarerequire revalidation. It is highly unusual to implement changes of the magnitude incorporated into Version4.8 without having to adjust your model to maintain validation even when comparable functions are used.

The reduction in VMT is not uniform throughout the study area. The following images provide examples of24-hour volumes for both version 4.7 (blue box) and version 4.8 (green box) for a diverse set of areas. Nopattern was discernable but there are roadways where the volumes are higher in version 4.8. See the SH-9 /SH-288 area (figure 4) and US-67 / SH-5 area (figure 6) in the figures below.


Figure 2; Downtown Little Rock area


Figure 3; I-30, I-530, I-440 area


Figure 4; SH-9, SH-298 area


Figure 5; US-65, SH-225, SH-285 area


Figure 6; US-67, SH-5, SH-321 area

Model DeliveryThe final version of the updated CARTS model has been packaged as a self-extracting file that uses the sameinstallation steps as the original version. Alliance has also coordinated with CARTS staff to ensure that thedesired version of the networks and demographics are included.


RECOMMENDATIONS

It is not uncommon for a revalidation to be performed when upgrading software to account for minorvariations in results across software versions. However, due to the imminent release of TransCAD 5.0 andthe fact that the model is functional in TransCAD 4.7, it seems unnecessary to proceed with a revalidationof the 4.8 version of the model.

CARTS specifically excluded network coding from this work authorization since it was an item that stafffelt could be performed in-house. Therefore no highway or network coding was performed other than tocorrect obvious errors that directly impacted the update. However, during the work, TransCADconsistently reported warnings in both Version 4.7 and 4.8 concerning unconnected transit stops andoccasionally regarding other network issues. It is recommended that a review of the transit route systemcoding be undertaken to resolve any possible issues.


APPENDIX B – TECHNICAL MEMO ON REVALIDATION

Memorandum

To: Richard Magee, Metroplan

From: Casey R. Covington, Metroplan

Date: May 13, 2008

Re: CARTS Model Delay Equation Revalidation

This memorandum describes and summarizes the effort in recalibrating the CARTS Model Delay Equationfor TransCAD 4.8. Initially, modifications to the delay equation were reviewed and model runs werecompleted on various sets of coefficients (Series 1 test). The model network was then reviewed andmodifications were made to centroid connectors and facility types to improve the accuracy of the model inreproducing 2000 base year counts. Using the revised network, a second set of model runs were thencompleted (Series 2 Test).

DELAY EQUATION

The CARTS Model uses the Logit-delay Equation built into TransCAD which assigns both link andintersection delay (signalized). The recalibration effort focused on the link delay equation uses 4coefficients: C1, C2, C3, and C4. The C1 coefficient has little impact on the delay equation and istypically calculated based on C2, C3, and C4 coefficients. The CARTS Model (TransCAD 4.7) usesstandard values for C2 and C4 coefficients; the C3 coefficient is facility specific with the default used forarterials/collectors and freeways using an adjusted coefficient. Recalibration review looked atmodifications to C2, C3, and C4. Figure 1 shows congested speeds based on V/C ratios for freeways (60mph freeflow) and arterials (40 mph freeflow) from TransCAD 4.7.

Logit-Based Volume Delay Function (Link Delay)

D1=t0 * c1 * {1/[1-(c2/(1+exp(c3-c4(x/C)))]}

D1 = Link Delay

T0 = Free-flow Travel Time

X = Traffic Flow

C = Lnk Capacity

c1, c2, c3, c4 = Coefficient


Default Values

C1 = .9526

C2 = 1

C3 = 3 (2.5 Freeways CARTS Model)

C4 = 3

Figure 1: CARTS Model Delay Equation


TRANSCAD 4.7 ACCURACY

Figures 2 and 3 below show the accuracy of the TransCAD 4.7 model by volume.

Figure 2: TransCAD 4.7 Freeway Stations

Figure 3: TransCAD 4.7 Surface Streets


SERIES 1

A series of tests were completed on the CARTS Model (TransCAD 4.8) modifying the C2, C3, and C4coefficients to determine an optimum result. These test included modifying the C2 value from 1.0(default) to .9, C3 values ranging from 2.5 (TransCAD 4.7) to 3.1 for freeways and from 3.0 (default) to3.7 for arterials and collectors, and C4 modifications between 3.0 (default) and 2.3. Tables 1 through 5show the results of these tests with the calculation of RMSE and VMT. In tables 2 the results arecalculated for are all freeway links, freeway links with a V/C less than .7, freeway links with a V/Cgreater than .7, and freeway links with a V/C greater than .9. In table 4 the results are calculated forarterials and collectors, links are subdivived into traffic counts less than 5,000, between 5,000 and 9,999,and those with a traffic count of 10,000 or more.

Table 1: RMSE and VMT for All Facility Types

Counts RMSE VMT Counts VMT Links withCounts

Percent of VMT

2000 4.7 Base 1114 29.43% 7,607,093 7,671,848 100.9%

2000 4.8 Base 1114 31.44% 7,607,093 7,254,379 95.4%

2000 4.8 C2 = .90 1114 49.34% 7,607,093 8,248,113 108.4%

2000 4.8 C2 = .95 1114 48.77% 7,607,093 8,182,860 107.6%

2000 4.8 C3 = 3.0 & 3.5 1114 30.15% 7,607,093 7,745,767 101.8%

2000 4.8 C3 = 3.1 & 3.7 1114 30.50% 7,607,093 7,844,216 103.1%

2000 4.8 C4 = 2.7 1114 29.74% 7,607,093 7,491,555 98.5%

2000 4.8 C4 = 2.6 1114 29.58% 7,607,093 7,565,715 99.5%

2000 4.8 C4 = 2.5 1114 29.76% 7,607,093 7,655,464 100.6%

2000 4.8 C4 = 2.4 1114 30.37% 7,607,093 7,750,357 101.9%

2000 4.8 C4 = 2.3 1114 31.02% 7,607,093 7,828,694 102.9%


Table 2: RMSE Calculated Freeways

All Freeways V/C Ratio < .7 V/C Ratio >= .7 V/C Ratio >=.9

Counts RMSE Counts RMSE Counts RMSE Counts RMSE

2000 4.7 Base 19112.49%

8917.22%

1029.82%

429.37%

2000 4.8 Base 19115.49%

8917.17%

10214.40%

4214.81%

2000 4.8 C2 = .90 19136.97%

8939.52%

10235.01%

4233.90%

2000 4.8 C2 = .95 19136.33%

8938.88%

10234.39%

4233.29%

2000 4.8 C3 = 3.0 & 3.5 19113.02%

8919.71%

1028.97%

428.52%

2000 4.8 C3 = 3.1 & 3.7 19113.97%

8921.41%

1029.40%

428.74%

2000 4.8 C4 = 2.7 19113.30%

8917.78%

10214.40%

4210.67%

2000 4.8 C4 = 2.6 19113.20%

8918.56%

10210.81%

429.78%

2000 4.8 C4 = 2.5 19113.05%

8918.64%

10210.15%

429.29%

2000 4.8 C4 = 2.4 19113.61%

8919.76%

1029.82%

429.68%

2000 4.8 C4 = 2.3 19114.27%

8920.81%

10210.02%

4210.04%

Table 3: VMT Calculated Freeways

4.7 Base 4.8 Base4.8 C2 =

.904.8 C2 =

.954.8 C3 =3.0 & 3.5

4.8 C3 =3.1 & 3.7

4.8 C4= 2.7

4.8 C4= 2.6

4.8 C4= 2.5

4.8 C4= 2.4

4.8 C4 =2.3

VMT 7.97 7.41 9.41 9.32 8.17 8.32 7.80 7.90 8.04 8.16 8.28

VMT Counts 5.12 5.12 5.12 5.12 5.12 5.12 5.12 5.12 5.12 5.12 5.12

VMT Links with Counts 4.96 4.63 5.82 5.76 5.10 5.19 4.87 4.93 5.01 5.10 5.17

Percent of VMT 97.0% 90.4% 113.7% 112.5% 99.5% 101.4% 95.1% 96.3% 97.9% 99.5% 101.0%

*VMT shown in millions


Table 4: RMSE Surface Streets

All Surface Count < 5,000 Count 5000 to 9999 Count =< 10,000


2000 4.7 Base 91542.06%

418103.59%

21437.87%

28327.89%

2000 4.8 Base 91543.07%

41898.09%

21437.52%

28329.47%

2000 4.8 C2 = .90 91549.42%

41897.01%

21451.63%

28333.66%

2000 4.8 C2 = .95 91549.29%

41896.39%

21451.47%

28333.59%

2000 4.8 C3 = 3.0 & 3.5 91542.94%

418102.23%

21440.09%

28328.57%

2000 4.8 C3 = 3.1 & 3.7 91542.80%

418103.44%

21440.29%

28328.28%

2000 4.8 C4 = 2.7 91542.02%

41898.08%

21438.18%

28328.31%

2000 4.8 C4 = 2.6 91541.82%

41899.04%

21439.98%

28327.88%

2000 4.8 C4 = 2.5 91542.22%

41899.56%

21439.22%

28328.21%

2000 4.8 C4 = 2.4 91542.85%

418100.70%

21441.29%

28328.41%

2000 4.8 C4 = 2.3 91543.46%

418102.74%

21443.63%

28328.46%

Table 5: VMT Calculated Surface Streets

4.7 Base 4.8 Base4.8 C2 =

.904.8 C2 =

.954.8 C3 =3.0 & 3.5

4.8 C3 =3.1 & 3.7

4.8 C4 =2.7

4.8 C4 =2.6

4.8 C4 =2.5

4.8 C4 =2.4

4.8 C4 =2.3

VMT 9.83 9.54 8.40 8.38 9.50 9.49 9.47 9.49 9.51 9.49 9.50

VMT Counts 2.48 2.48 2.48 2.48 2.48 2.48 2.48 2.48 2.48 2.48 2.48

VMT Links with Counts 2.70 2.61 2.42 2.41 2.63 2.64 2.61 2.62 2.63 2.64 2.65

Percent of VMT 108.8% 105.5% 97.6% 97.2% 106.0% 106.5% 105.3% 105.9% 106.2% 106.7% 106.9%

*VMT shown in millions

From this series of test, it was determined that the coefficients resulting in the closest replication of baseyear traffic volumes in TransCAD 4.8 were C3 values of 3.0 (freeways) & 3.5 (arterials) or a C4 value of2.5. Modifications to the C2 value were not found to be beneficical and were dropped fromconsideration. Graphs showing the accuracy of the model for these coefficients are found in the series 2test.


SERIES 2

After the completion of series 1 test, areas of the model which were performing poorly were reviewed andcentroid connector and/or facility type changes were made. These changes were then tested in TransCAD4.7 to determine which ones had an overall positive impact on the models ability to reproduce 2000 trafficvolumes. Once these changes were made in TransCAD 4.7 they were implemented in TransCAD 4.8runs. Series 2 tests included model runs with the updated centroid connectors for 2000, 2010, 2030 inTransCAD 4.7 and TransCAD 4.8. Coefficients for C3 and C4 were also modified based on the resultsfrom Series 1 test. These tests are shown in Table 6 below.

Table 6: Series 2 Test

Freeways Arterials

Year C1 C2 C3 C3 Peak C4 C1 C2 C3C3

Peak C4

Default Values .9526 1 3 3 .9526 1 3 3TransCAD

4.7 & 4.8 2000-2010-2030 0.9526 1 2.5 2 3 0.9526 1 3 2.5 3

2000 1a 0.9526 1 2.5 2 2.5 0.9526 1 3 2.5 3TransCAD4.8

2000 1b 0.9526 1 2.5 2 2.4 0.9526 1 3 2.5 3

2000 2a 0.9526 1 3 2.5 3 0.9701 1 3.5 3 3TransCAD4.8

2000 2b 0.9570 1 3.1 2.5 3 0.9760 1 3.7 3 3

RMSE and VMT comparisons were made between the different model runs. Tables 7 through 11 showthe results of these comparisons. Overall the four scenarios tested preformed well and were comparableto the results from TransCAD 4.7.

Table 7: RMSE and VMT for All Facility Types

Counts RMSE VMT Counts VMT Links withCounts

Percent of VMT

2000 4.7 Base 1116 26.94 7,566,572 7,645,436 101.04%

2000 4.8 Base 1116 28.05 7,566,572 7,209,836 95.29%

2000 4.8 1a 1116 27.51 7,566,572 7,620,021 100.71%

2000 4.8 1b 1116 27.99 7,566,572 7,689,794 101.63%

2000 4.8 2a 1116 27.26 7,566,572 7,707,136 101.86%

2000 4.8 2b 1116 27.45 7,566,572 4,794,438 103.01%


Table 8: RMSE Calculated Freeways

All Freeways V/C Ratio < .7 V/C Ratio >= .7 V/C Ratio >=.9


2000 4.7 Base 19612.63

9417.92

1029.35

428.65

2000 4.8 Base 19614.76

9416.91

10213.42

4213.68

2000 4.8 1a 19613.86

9420.05

1029.98

429.66

2000 4.8 1b 19614.45

9420.72

10210.54

429.73

2000 4.8 2a 19613.85

9420.71

1029.40

428.65

2000 4.8 2b 19614.17

9421.36

1029.47

428.61

Table 9: VMT Calculated Freeways

4.7 4.8 4.8 1a 4.8 1b 4.8 2a 4.8 2b

VMT 8,052,316 7,486,653 8,094,096 8,213,323 8,210,286 8,301,023

VMT Counts 5,120,713 5,120,713 5,120,713 5,120,713 5,120,713 5,120,713

VMT Links with Counts 5,010,176 4,673,869 5,047,894 5,118,498 5,118,145 5,178,012

Percent of VMT 97.8% 91.3% 98.6% 100.0% 99.9% 101.1%

Mean (Percent of Counts) 99.70% 92.78% 100.28% 101.68% 101.60% 102.54%

Median (Percent of Counts) 99% 93% 100% 102% 102% 102%

Table 10: RMSE Calculated Surface Streets

All Surface Count < 5,000 Count 5000 to 9999 Count =< 10,000


2000 4.7 Base 912 37.74 416 95.95 214 36.44 282 24.34

2000 4.8 Base 912 37.75 416 90.45 214 34.57 282 25.20

2000 4.8 1a 912 37.65 416 93.35 214 38.38 282 24.15

2000 4.8 1b 912 37.94 416 92.29 214 39.56 282 24.34

2000 4.8 2a 912 37.20 416 94.82 214 37.59 282 23.66

2000 4.8 2b 912 37.21 416 97.06 214 38.78 282 23.21

Table 11: VMT Calculated Surface Streets


4.7 4.8 4.8 1a 4.8 1b 4.8 2a 4.8 2b

VMT 9,604,324 9,252,238 9,240,329 9,238,053 9,348,382 9,417,067

VMT Counts 2,437,805 2,437,805 2,437,805 2,437,805 2,437,805 2,437,805

VMT Links with Counts 2,624,736 2,526,855 2,563,338 2,562,607 2,579,509 2,606,722

Percent of VMT 107.7% 103.7% 105.1% 105.1% 105.8% 106.9%

In addition to the calculation of RMSE and VMT results, the accuracy of the model for different scenarioswas also graphed. These results are shown in the following figures.




Figure 6: TransCAD 4.8 1a Freeway Stations


Figure 7: TransCAD 4.8 1b Freeway Stations

Figure 8: TransCAD 4.8 2a Freeway Stations


Figure 9: TransCAD 4.8 1b Freeway Stations




Figure 12: TransCAD 4.8 1a Surface Streets


Figure 13: TransCAD 4.8 1b Surface Streets

Figure 14: TransCAD 4.8 1a Surface Streets


Figure 15: TransCAD 4.8 1b Surface Streets

After reviewing results from the series 2 tests, it was determined that scenario 2a most closely replicated2000 traffic volumes. Under this scenario, the linear regression line is constant at 1.01, with 80% offreeways stations predicting within 20% of their volume and 53% of freeways stations predicting within10% of their volume. The accuracy of the model on arterials is less at volumes under 10,000 which iscommon. The regression (moving average method) shows that on average volumes are replicate at 137%at a volume of 5000, 100% at volumes of 10,000, before leveling off at 90% for high volume locations.

RECOMMENDED DELAY EQUATION MODIFICATIONS

Based on the results from the series 2 test, a delay equation modification to scenario 2a is recommended.This scenario most closely reproduces base year traffic volumes and that of TransCAD 4.7.

Table 12: CARTS Model Delay Equation

Freeways Arterials

C1 C2 C3 C3 Peak C4 C1 C2 C3C3

Peak C4

Default Values 0.9526 1 3 3 0.9526 1 3 3

TransCAD 4.7 0.9526 1 2.5 2 3 0.9526 1 3 2.5 3TransCAD 4.8

(Recommended) 0.9526 1 3 2.5 3 0.9701 1 3.5 3 3


The revised delay equation is shown in Figure 16 with comparisons to the original BPR Curve (OldCARTS TranPlan Model) and the more recently calibrated BPR curve (based on the Highway CapacityManual). At volume to capacity ratios less than 1 the Logit Delay Functions results in speed estimatesbelow that of the calibrated BPR curve. At volume to capacity ratios above one the Logit Delay Functionresults in speed estimates higher than the BPR curve.

Figure 16: Carts Model Recommended Delay Equation


2030 TRAVEL DEMAND MODEL RESULTS

Following recalibration of the 2000 model, scenario 2a (C3 = 3.0 freeways and C3= 3.5 arterials) was runon TransCAD 4.8 using socioeconomic data for 2030. For each facility type the system wide VMT grewby 47% to 50% between 2000 and 2030. This growth is slightly larger than the forecast populationgrowth of 42.6%. The percent growth of VMT for each facility type is shown in Table 12. Figures 17and 18 the percent growth for traffic count locations, these graphs show that the higher percent trafficgrowth is for count locations with lower volumes were additional capacity exist.

Table 12: 2000 to 2030 Travel Model Comparisons

2000 2030 Percent Growth

Network VMT 19,345,861 28,767,947 48.7%

Freeway VMT 8,210,286 12,084,185 47.2%

Arterial & Collector VMT 9,348,383 13,999,340 49.8%

Frontage Road/Ramp VMT 503,866 748,815 48.6%

Centroid Connector VMT 1,283,325 1,935,606 50.1%

Population 583,845 832,591 42.6%

Figure 17: Percent Forecast Growth Freeways (Growth calculated as modeled to forecast)

*Count locations directly impact by roadway improvements have been removed


Figure 18: Percent Forecast Growth Surface Streets (Growth calculated as modeled to forecast)

*Count locations directly impact by roadway improvements have been removed


APPENDIX C – SCREENLINE ROADWAYS

The following table contains the names of roadways that are part of each Screenline/Cutline.

Screenline/Cutline Road Name Highway1 I-430 I- 4301 Broadway Brdg US Hwy 701 Main St Brdg Ark 51 I- 30 I-301 I- 440 I-4402 US Hwys 67/167 US 672 Fairway 2 North Hills2 JFK Blvd Ark 1072 Camp Robinson Rd Ark 1763 I- 40 I-403 State Hwy 365 Ark 3654 I- 40 I-404 Military Rd Ark 2944 Graham Rd 4 State Hwy 321 Ark 3214 State Hwy 367 Ark 3674 US Hwys 67/167 US 675 State Hwy 25 Ark 255 US Hwy 65 US 656 US Hwy 70 US Hwy 706 State Hwy 5 Ark 56 Steel Bridge Rd 6 State Hwy 298 Ark 2987 US Hwy 67 US 677 I- 30 I-308 US Hwys 65/167 I-5308 State Hwy 365 Ark 3659 I-40 I-409 US Hwy 70 US Hwy 709 US Hwy 165 US Hwy 1659 Faulkner Lake Rd 10 W Roosevelt Rd US Hwy 7010 Wright Av 10 W 14th St 10 W 12th St10 I-630 I-63010 W 7th

10 W 3rd

10 Cantrell Ark 1011 E Roosevelt Rd


11 I-440 I-44011 Frazier Pike12 Pike Av Hwy 36512 N Main St 12 I- 30 I-3013 I- 40 I-4013 MacArthur Dr Ark 36514 US Hwy 67 US 6714 State Hwy 161 Ark 16115 S University Av US 7015 Mabelvale Pike 16 Mann Rd 16 I- 30 I-3016 Baseline Rd Ark 33816 Mabelvale Pike 17 I- 30 I-3017 Old Stagecoach Rd Ark 518 State Hwy 319 Ark 31918 US Hwys 67/167 US 6718 State Hwy 367 Ark 36719 State Hwy 107 Ark 10719 US Hwys 67/167 US 6719 N 2nd St Ark 36719 N Lincoln St Ark 3820 I- 40 I-4020 US Hwy 70 US Hwy 7021 Carson Bridge Road21 I- 40 I-4021 US Hwy 70 US Hwy 7022 Hilaro Springs Rd 22 Arch Street Pike Ark 36722 US Hwys 65/167 I-53022 Dixon Rd Ark 33823 I- 30 I-3023 US Hwys 65/167 I-53024 I-430 I- 43024 S Shackleford Rd 24 Old Stage Coach Rd Ark 525 W 36th St 25 Colonel Glenn Rd Ark 30027 N Chester St 27 N State St 27 N Broadway US Hwy 7029 US Hwy 65 US 6529 State Hwy 287 Ark 28729 Acklin Gap Rd 29 State Hwy 36 Ark 36


30 US Hwy 165 US Hwy 16530 State Hwy 232 Ark 23231 Colonel Glenn Rd 31 Chenal Pkwy 32 S German Ln 32 Sturgis Rd 32 S Donaghey Av Ark 60 Spur33 N. Rodney Parham Rd33 Markham33 I-630 I-63033 Kanis33 W. 30th34 I-63034 Markham


APPENDIX D – LETTER OF ACCEPTANCE

August 26, 2008

ACCEPTANCE OF CARTS TRAVEL DEMAND MODEL

TO WHOM IT MAY CONCERN:

Review of the CARTS Travel Demand TransCad Model by staffs from both agencies determined that themodel is performing acceptably for both the 2000 base year and 2030 forecast year. As such, the CARTSModel Version 05.16.08 is now accepted for use as the official travel demand forecast model for Faulkner,Lonoke, Pulaski, and Saline counties. All future planning and operation studies should use this model versionas a tool to determine official traffic and transit forecast data.

The CARTS Model Version 05.16.08 should be used as the base from which future model refinements forindividual projects should also be built. At such time that the CARTS Model Version 05.16.08 needsupdating as defined in the attached memorandum names “Model Version” between Metroplan and theArkansas Highway and Transportation Department, the new version of the model should become the defaultofficial CARTS model.

ATTESTED TO:

Richard K. Magee Virginia H. PortaMetroplan Arkansas Highway and Transportation DepartmentCARTS Study Director Staff Planning Engineer

Planning and Research Division

_______________________ _______________________


MEMORANDUMFrom: MetroplanTo: AHTDSubject: Model VersionDATE: 8/26/08 (Original 8/16/05)___________________________________________________________

It is recognized that the official CARTS Travel Demand Model will need to be updated on occasion. Whenthis becomes necessary, the model version as updated becomes the accepted official version of the modelupon mutual agreement of both agencies (Metroplan and AHTD). However, for most projects, the officialversion can and should remain the same with any edits remaining only for an individual project.

Official Version

Naming Convention

The official version of the model is identified by the date on which it is created. The current official versionof the model is CARTS TDM 05.16.08. This official version should be maintained by each agency on both aCD and computer hard drive.

Official Version Updating

When it is determined by either agency that the official model version needs updating, the proposing agencyshould revise the official version as needed and then notify the other agency via a memo of all documentedchanges. The receiving agency must then review and concur with all documented changes before a newofficial model version is declared, dated and provided to both parties. Both parties should routinely createbackup copies of the official model version.

Individual Projects

Most projects do not require the official version of the model to be updated. In these cases, the officialversion should simply be copied and named as an individual project and then edited as needed. A copy of theindividual project should then be saved on CD and/or hard drive.

Copy Convention

It is important to create copies of the official version of the model and individual projects that are createdfrom this official version. A copy should be created by copying the entire contents of the CARTS Modelfolder to a new folder. For a backup of the official version, a new folder should be created on the hard driveto identify it as the official version (CARTS TDM 05.16.08) and the contents of the CARTS Model added tothese folder. A separate folder should be created where all individual projects are stored. Many projects canbe stored in this folder using various subfolders. Once edits have been made for a project, the contents of theCARTS Model folder should be pasted into this folder. Due to size it will be necessary to save projects onCDs or DVD periodically.

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