Trip Generation at the Site Level

Norman W. Garrick

Trip Rate Analysis

Typically used to estimate trips from sites rather than for whole cities or region

Used for so-called traffic impact study

Norman W. Garrick

Trip Rate Analysis

Trip-Rate AnalysisTrip rate is estimated based on the characteristics of the trip generator or trip attractor.

Example

The characteristics of the trip generator is given in 1000 SQ. FT.And the trip generation rate for each generator is given as TRIPS PER 1000

SQ. FT.

For exampleResidential: Total Sq. Ft. = 2744 1000 sq. ft., Trip Gen. Rate = 2.4 trips/1000

sq.ftTOTAL NO. of TRIP from residential land use = 2744*2.4 = 6586 Trips

Norman W. Garrick

ITE Trip Generation Manual

Norman W. Garrick

ITE Trip Generation ManualLow Rise Apartment, Weekday

Norman W. Garrick

ITE Trip Generation ManualLow Rise Apartment, Weekday

19 data points!

Norman W. Garrick

ITE Trip Generation ManualLimitations

The data contained in Trip Generation are, by definition, from single-use developments where virtually all access is by private automobile and all parking is accommodated on site.

For new developments with characteristics that reduce automobile use--located close to transit, containing a mix of uses, or charging for parking--the use of unadjusted average ITE trip-generation rates will in many cases drastically overestimate the amount of traffic generated.

A corner store with no parking across from a subway station in a dense, transit-oriented development is often forecast to have the same impact as a 7-Eleven on a suburban highway.

Ref: Playing the numbers game: when it comes to TODs, trip-generation figures can make all the difference

by Millard-Ball, Adam, Siegman, Patrick http://www.entrepreneur.com/tradejournals/article/158211933.html

Norman W. Garrick

ITE Trip Generation ManualDangers of Overbuilding

"The traffic engineering profession is just waking up to the fact that one can overbuild infrastructure so it no longer serves the community," continues Walters (a California-based principal at Fehr & Peers Associates). "When one tries to design facilities to cater to the maximum demand that may occur, one can end up with too much.

"It's true of parking," Walters says. "It's also true of streets," where oversizing can lead to more lanes, wider lanes, and longer signal phases than are strictly warranted. This not only adds to development costs but reduces the amount of space available for trees and other amenities, and creates physical barriers in the community.

Ref: Playing the numbers game: when it comes to TODs, trip-generation figures can make all the difference

by Millard-Ball, Adam, Siegman, Patrick http://www.entrepreneur.com/tradejournals/article/158211933.html

Norman W. Garrick

Storrs Center Model

Norman W. Garrick

Storrs Center Model Village Road

Norman W. Garrick

Storrs Center

Norman W. Garrick

Storrs Center Google Earth The Site

Norman W. Garrick

Storrs Center Google Earth The Site Constraints

Wetlands

Forest Reserve

Norman W. Garrick

Storrs Center Google Earth The Site Built Area

Norman W. Garrick

Storrs Center Model Village Road

Norman W. Garrick

Using TG Manual for Storrs Center

Estimated number of trip ends = 24,600

ITE Trip Generation Manual

Proposed size of project

Norman W. Garrick

Using TG Manual in Storrs Centerwith Correction for Mixed Use

Estimated number of trip ends = 15,900

This estimate almost lead to the unnecessary widening of Storrs Road.

The widen was prevent by change the design of the town center by providing two roads into the center not one as was originally design.

Norman W. Garrick

Storrs Center 195 Problem

Norman W. Garrick

Storrs Center Importance of the Network

Modifying ITE for Mix Use

The ITE procedure estimate 24,600 trip ends for Storrs Center

In many projects this number is assumed to be the number of new VEHICLE trips

Because Storrs Center is a mixed use, walking center that is close to the university the assumption that these are all vehicles is significant wrong.

Estimating Number of New Vehicle Trips

Factors Affect % of Trips that are Vehicle Trips•Mode Share •Mixed Use (internal capture)•Pass By Trips •Vehicle Occupancy Rate

Estimating Reduction from ITEfor Storrs

Mode Share – 50 % (walk, bike, transit)Mixed Use (internal capture) – 35 % Pass By Trips – 25 %Vehicle Occupancy Rate – 10 %

Estimated New Vehicle Trips = 4700 per day

Estimating Number of New Vehicle Tripsfor Storrs

Mode Share = 0.5 * 24,600 = 12,300Number of Vehicle Trips Accounting for Mode Share = 24,600 – (0.5*24,600) = 12,300

Amount of reduction due to Mixed Use = 0.35*12,300 = 4,305Amount of reduction due to Pass By Trips = 0.25*12,300 = 3,075Amount of reduction due to Vehicle Occupancy Rate = 0.10*12,300 = 1,230

Estimated New Vehicle Trips = 12,300 – (4,305 + 3,075 + 1,230) = 3,690

360 State, New Haven Actual versus Predicted New Trips

360 State, New Haven trip Generation over predict trips

The 360 State Street was estimated to produce 674 PM peak hour vehicle tripsRequiring the construction of 500 parking spaces

Live monitoring shows only 116 trips (17% of what was predicted)

- Mixed Use Trip Generation Model (New Haven and SCRCOG)