transportation & traffic...

By: Armando Gomez-Farias

Transportation & Traffic Engineering

1) Project Description – Executive Summary

This report presents a summary of findings for a Traffic Engineering Study performed

by A+ Engineering, Inc. for the Hill Country Family Fitness Center Project located north

of US Hwy 281 and Hwy 46 in Spring Branch, Texas as shown in Figure 1. This project

is within the Comal County jurisdiction and therefore will comply with all of Comal

County regulations.

Figure 1: Site Location

The Hill Country Family Fitness Center Project consists of a 52,500 square-feet (SF)

building that will serve as a fitness club for the Rodeo Subdivision and adjacent

neighborhoods of the area. The project is anticipated to be completed by the end of 2014.

2) TIA Introduction

Given that the access point of the proposed development is towards Rodeo Drive, a

county road, Comal County is the reviewing authority for the transportation aspect of the

project and the authority to provide driveway permits. Comal County does not require


traffic impact analysis (TIA) to be performed for the proposed development.

Nevertheless, the Transportation Engineering team has followed the City of San Antonio

TIA guidelines to comply with the Texas Department of Transportation requirements

since the proposed development is located near US Highway 281. The analysis and

design calculations and procedures have conformed to the following codes and entities:

City of San Antonio – Unified Development Code, Institute of Transportation Engineers’

Trip Generation Manual, 8th Edition, the TxDOT’s Roadway Design Manual, and the

Transportation Research Boards Highway Capacity Manual, 2000.

Article V, Section 35-502 of the COSA – UDC states that if the amount of peak hour

trips generated by a proposed development is between 76 and 150, it will require a traffic

impact analysis (TIA) Level I. Since the PHT generated by the proposed development are

213 (see Section 3 for more details), A+ Engineering Design was retained to prepare a

Level I Traffic Impact Analysis (TIA) for the Hill Country Family Health Fitness Center.

A meeting was conducted with city public works on October 24th, 2013 to determine

the requirements and scope of the TIA in accordance with generally accepted practice.

The meeting determined the type of study, study area, trip generation, trip distribution

and assignment, time period of analysis, and established growth rate.

This study assesses the transportation impacts of the proposed development on the

thoroughfare to review site access and circulation as required by Sections 19-82 and 19-

84 of the Code of Ordinances for the City of San Antonio. The following sections provide

a detailed report of the analyses performed by A+ Engineering Design.

3) Trip Generation

The first step was to estimate the traffic generated by the new development proposed.

The generated traffic was determined using the ITE Trip Generation, 9th Edition by the

Institute of Transportation Engineers. This manual was used to estimate the number of

trips ends that may be generated by the construction project. The number of trips

generated by the development is a function of the type and quantity of the land use of the

development. The proposed development is categorized as Land Use 492 (Health/Fitness


Club) in the ITE Trip Generation, 9th Edition. This land use is for privately owned

facilities that primarily focus on individual fitness or training. Typically they provide

exercise classes, weightlifting, fitness and gymnastics equipment; spas; lockers rooms;

and small restaurants or snack bars. This land use may also include ancillary facilities,

such as swimming pools, whirlpools, saunas, tennis, racquetball and handball courts and

limited retail. These facilities are membership clubs that may allow access to the general

public for a fee.

The gross floor area was selected as the independent variable, which is a measurable

and predictable unit describing the study site that can be used to predict the value of the

dependent variable (trip ends). The gross floor area of a building is defined as the sum (in

square feet) or the area of each floor level that are within the principal outside faces of

exterior walls. The proposed development has a total gross floor area of 52,500 square

feet.

The average rate of generated traffic for a Health/Fitness club during a weekday AM

peak hour is 1.41 trips per 1000 square feet of gross floor area with a 1.5 standard

deviation. Following the ITE Trip Generation recommendation of using the average rate

if the standard deviation is no more than 10% greater than the average rate:

1.51.41

100% = 1.10 ≤ 1.10

we were able to calculate the generated traffic during the AM peak hour. The results are

summarized in Table 1.

The average rate of generated traffic during a weekday PM peak hour is 4.06 trips

per 1000 square feet of gross floor area with a 2.02 standard deviation. Following the ITE

Trip Generation recommendation of using the average rate if the standard deviation is no

more than 10% greater than the average rate:

4.062.02

100% = 0.50 ≤ 1.10

we were able to calculate the generated traffic during the PM peak hour. The results are


summarized in Table 1.

Gross Floor Area

(1000 sq.ft.) 52.5

Weekday

Generator AM Peak

Weekday

Generator PM Peak

Trips / Unit 1.41 4.06

% Enter / % Exit 42% 58% 68% 32%

Total Trips 74 213

Enter / Exit 31 43 145 68

Table 1: Traffic Generation

As shown on Table 1, the maximum PHT that the proposed development will

generate, the Weekday Generator PM Peak, equals to 213 trips. According to the

threshold by the City of San Antonio, 76 PHT, a traffic impact analysis is required.

For this project, a traffic engineering study will be conducted to analyze the

capacity of the roadway with the development and ensure TXDoT requirements. This

study is discussed below

4) Trip Distribution and Traffic Assignment

The traffic generated was added to the road network based on the percentages of

traffic on each road obtained from the existing traffic demand (Task 1.1). The PHT from

Task 1.1 were distributed to subsequent intersections until the minimum of seventy-six

(76) PHT or a one and one-half (1.5) mile maximum distance was reached.

For this case, the PM PHT were used since they showed a greater number of traffic

generated and therefore are critical in the analysis. A map summarizing the trip

distribution for inbound and outbound PHT is shown in Figure 2 and Figure 3. These

figures show the PHT to be distributed along with the percentages of distributing and the

identified intersections to be analyzed.


Figure 2: Trip Distribution Network Diagram – Outbound

Figure 3: Trip Distribution Network Diagram - Inbound

The trip distribution analysis showed that the intersections that may be affected by

the new development are as follows (shown on Figure 1 & 2): Rodeo Drive and U.S.

Highway 281, Rodeo Drive and Texas Oaks, and Rodeo Drive and River Way. And after

a site visit on September 7,2013 the following information was gathered:


o Rodeo Drive:

§ Number of lanes: 1 eastbound / 1 westbound

§ Lane Width: 12 feet

§ Speed Limit: 30 mph

o US Highway 281

§ Number of lanes: 2 northbound / 2 southbound with 50 feet median



o Texas Oaks




§ 1 deceleration lane on US Hwy 281 to enter Rodeo Drive (350 ft.)

o River Way




o Traffic Signs

§ Stop sign at Rodeo Drive to enter US Hwy 281

§ 4-way stop sign in Rodeo Drive and Texas Oaks intersection

§ Stop sign at Rodeo Drive to enter River Way

5) Traffic Flow Analysis

This task consisted in a traffic flow analysis on Rodeo Drive and all adjacent streets

and intersections that were identified in the previous section. This traffic flow analysis


helped determine the existing conditions of the site and its vicinity and the existing traffic

demand. The analysis provided us with the following information: peak hour factor

(PHF), trip distribution percentages, number of peak hour trips (PHT), and percent trucks.

Traffic counts were gathered for the three identified critical intersections from

Section 1.2. The traffic data was gathered for the AM (7:00 – 9:00) and PM (4:00 – 6:00)

peak hours. The right-turn, left-turn, and thru traffic for all directions (north, south, east,

and west) were counted. These counts were then used to calculate the peak hour, peak

hour factor, percentage of trucks, peak hour turning movements, and peak hour turning

percentages. The spreadsheets including all the information and results for the AM and

PM counts for all three intersections are provided at the end of the report. These counts

were then used to perform the capacity analyses using Synchro, which is describe in the

next section.

6) Traffic Impact Analysis (TIA):

The purpose of this analysis is to identify travel responses in routing, scheduling, and

traffic flow due to the new construction project. This is accomplished by combining the

existing traffic volumes plus the forecasted conditions that will develop. The forecast of

future traffic flow and impact will reflect the traffic conditions once the new construction

has been finalized and the health center is fully operational.

With all information about the intersections that was gathered in Section 1, the

intersections were analyzed using Synchro8 traffic analysis software. The Synchro

analysis provided the existing LOS (level of service) of each intersection. For this

project, only the PM hour was analyzed due to the fact that both the existing volumes and

the generated traffic volumes were both greater for the PM peak hour and therefore

making that hour more critical than the AM peak hour.

a. Existing Conditions

Based on the peak hour volumes computed from the traffic counts of the

three identified critical intersections, a Synchro model was created. This model


contained all the information gathered such as the geometry, traffic volumes

information. A visual model of the input information is summarized in Figure 3.

Figure 4: Volume Summary of Existing Conditions

The Synchro report for this model is provided at the end of this report. The

Synchro report showed a level of service (LOS) of A for all three intersections

analyzed. These levels of service will be used as a benchmark to compare the

forecasted conditions.

b. Forecasted Conditions

For the forecasted conditions, a model with the generated traffic plus the

expected traffic growth was analyzed. Using the compound formula, 𝑉!! =

𝑉!! 1 + 𝐺!, where G represents the growth rate and n represents the number of

years, a projection 5 year future volume of traffic was calculated. The growth rate

was conservatively chosen as 5% growth per year. With these numbers a Build

plus 5 years scenario was analyzed. The analysis included the 5-year projection

and the development generated traffic. Figure 4 shows a summary of the

generated traffic volumes and Figure 5 shows a summary of the generated traffic

plus the existing conditions after a five-year projection.


Figure 5: Volume Summary of the Generated Traffic

Figure 6: Volume Summary of the 5 Year Projection

The Synchro report for this model is provided at the end of this report. The

Synchro report showed a level of service (LOS) of A for all intersections

analyzed.

Synchro LOS

US 281 &

Rodeo Dr.

Texas Oak &

Rodeo Dr.

River Way &

Rodeo Dr.

Existing Conditions A A A

5 Year Projection A A A

Table 2: Level of Service of Identified Intersections


7) Conclusion and Recommendations

The Transportation Engineering team has used the TIA results to

determine if any changes to the existing roadway are needed. The forecasted LOS

was compared with the previous existing LOS. Since the LOS does not change,

no modifications nor any permission to mitigate traffic are necessary.

a. Deceleration Lanes

Comal County regulations do not require a deceleration lane to be

implemented on the county road, Rodeo Drive. For the COSA-UDC and TxDOT,

the maximum peak hour left-ins or right-ins must not exceed 50 PHT. The

proposed development exceeds this threshold in the right-ins (96 PHT).

Therefore, the A+ Engineering team recommends that a deceleration lane be

implemented to provide right-in turns easy access to the site.

Based on the TxDOT Roadway Design Manual Chapter 3 - Table 3.3 and

a street speed of 30 mph, a deceleration lane with 160 feet length, 50 feet taper

length and 100 feet long storage should be developed. Figure 7 provides a

schematic of the turn lane provided by TxDOT.

Figure 7: Deceleration Lane


Driveway and Site Access

The Transportation Engineering team also designed a proposed driveway to

accommodate the expected traffic and the Owner and Architects specifications.

The driveway design has been based on the regulations for access driveways to

roadways by the Texas Department of Transportation. The drive way will consist of 1 in-

lane and 1 out-lane. It will provide an access point from Rodeo Drive as shown in Figure

7. This access point will be aligned with the existing median opening.

Figure 8: Site Access

The asphalt pavement design consists of a 2 inch hot mix asphaltic concrete, a 14

inch granular base course (caliche), and a 6 in moisture conditioned subgrade at a 95%

compacted optimum density

The driveway has been design to comply with all Comal County and TXDoT

requirements, such as minimum radius, minimum throat, minimum slope, etc. The

drawings in the appendices provide a schematic of the layout of the driveway, the

dimensions, and the details of the driveway and asphalt.


The driveway has a 60 feet throat, 25 feet width, and 28 feet radii to ensure the

fire truck can easily access the site. The PIPROW Permit Application, permit required to

construct the driveway, has been submitted and approved by the Comal County

Engineers office; permit is provided in Appendix A.

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