ite trip generation pass by

• Forecasting

7  comments

Traffic Impact Study Improvements: Part 5 – When is a Trip Not a Trip?

By   Mike Spack

October 27, 2015

Guest Post by Bryant Ficek, PE, PTOE, Vice President at Spack Consulting

Earlier this year, I detailed how our standard process for a Traffic Impact Study has several points of assumptions at best or guesses at worst. This post continues that discussion.  Check out the “ Top 6 Ways to Pick Apart a Traffic Study ” for more on the general topic and expect more posts to follow on this subject.

Trip generation is the process of estimating the amount of traffic a proposed development will have once it is built and operating. Trip distribution is the process by which we take the raw projected traffic for a development (trip generation) and add it to the existing volumes on the transportation network. The step in-between is determining whether all the trip generation will be new to the roadway.

To start with, there are several types of trips as follows (with definition summarized from the Institute of Transportation Engineers or ITE). The figure below illustrates the different types of trips.

• Primary or New.  Traffic with the specific purpose of visiting the site being studied.
• Pass-By.  Traffic already on the way from an origin to a primary trip destination that will make an intermediate stop at the site being studied without a route diversion.
• Diverted. Traffic attracted to the site being studied from adjacent facilities without direct access to the site. A diverted trip example is a through trip on a freeway that diverts to an exit and a development, adding traffic to the local road but removing traffic from the freeway.
• Internal.  Traffic associated with multi-use developments where trips among various land uses can be made on the site being studied without using the major street system. These trips can be made either by walking or by vehicles using internal roadways.

These different trip generation options, combined with so many different types of land uses, leads to virtually limitless possibilities for the amount and type of traffic a particular site could generate on the roadway system. As with our trip distribution column, we initially thought about testing multiple scenarios, which would be relatively easy with today’s software. At least, theoretically. To restate our collective conclusion – While interesting on a pure research level, a thicker actual traffic impact study report covering multiple results leads us down a path no one wants to go.

Furthermore, sub-dividing the raw trip generation into parts is not something that can be quantified into a “one-size fits all” equation. Given the possibilities and the limits of our collective traffic research to date, ITE provides the best procedure to follow. So this article is dedicated to reviewing that procedure, which is spelled out in ITE’s Trip Generation Handbook and Trip Generation Manual, Volume 1 . That step-by-step process is as follows:

• Raw Trip Generation.  Using ITE or other land use information (try tripgeneration.org !), calculate the raw trip generation for the site.
• Pass-By and Diverted Number of Trips. Use either local data or ITE data to determine a percentage of the reduced trip generation that is pass-by or diverted. Similar to the ITE Trip Generation data, both pass-by and diverted trip percentages are available by average rate or an equation for many land uses. Use this percentage to calculate the total pass-by and diverted trips for the site.
• Pass-By and Diverted Trip Patterns. Use the existing traffic to determine how the pass-by and diverted trips will access the site.
• Pass-By and Diverted Trip Volume Adjustment. Apply the existing traffic patterns to the pass-by and diverted trips to establish the impact on the roadway system for these trips.
• Remaining Primary/New trips. Determine the remaining trip generation after reducing for internal trips and then removing the pass-by and diverted trips.
• Primary/New Trip Pattern. We discussed factors to consider for the primary/new trip distribution in Part 4 of this series.
• Primary/New Trip Volume Adjustment . Apply the trip distribution to the primary/new trips to determine the impact on the roadway system for these trips.
• Final Volumes. Combine the pass-by, diverted, and primary/new trips at each study intersection to determine the final impact of the site being studied.

We can demonstrate this process on a theoretical study site with the following characteristics:

• 17,000 square feet of office, 3,000 square feet of fast food with a drive-thru, and 10 vehicle fueling positions at a gas station with convenience market
• One driveway accesses the site off a busy road (1,000 vehicles in the p.m. peak hour)
• A highway interchange with the busy road is located just east of the site
• Trip Generation (PM Peak)
• General Office, Land Use 710 – 98 raw trips
• Fast Food with Drive Thru, Land Use 934 – 98 raw trips
• Gas Station with Convenience Market, Land Use 945 – 136 raw trips
• Internal Trips

4. Pass-By and Diverted Patterns (per the theoretical roadway data)

6. Remaining Primary/New trips:

• Office – (98 raw – 5 internal – 0 pass-by – 0 diverted) = 93 primary/new trips
• Fast Food – (98 raw – 21 internal – 43 pass-by – 23 diverted) = 11 primary/new trips
• Gas Station – (136 raw – 22 internal – 57 pass-by – 26 diverted) = 31 primary/new trips

7.  Primary/New Trip Pattern (per knowledge of theoretical area)

8.  Primary/New Trip Volume Adjustment

9.  Final Volumes (add the pass-by, diverted, and primary/new trips together)

We don’t include all of the above example graphs in our reports. Instead, our short-hand method is a trip generation table that looks like this:

As a final note, the internal, pass-by, diverted, and new percentages are often adjusted from the base ITE information. ITE itself notes the limited amount of data available and the inherent variability in surveyed sites. The best approach, if possible, is to discuss the percentages with the governing agency to achieve agreement and buy-in before you get too far down the path in your analysis.

Did you miss the other installments of the  Traffic Impact Study Improvements series? Here are the links to the other articles:

• Part 1 – Traffic Counts
• Part 2 – Would Multiple Results Help Us?
• Part 3 – All Trips are Equal, But Some Trips are More Equal Than Others

At what point would you apply a reduction for non-SOV trips such as transit? It looks like ITE would have you apply internal capture, transit and then pass-by.

very precious and informative post…thanks so much..I had found the answer of one of my question in another post of yours..thanks for sharing your experiences

Sometimes I drive right by a coffee shop and then think, hmm, I could really use a good cup of black coffee and then I turn around and go back. Is this a pass-by trip or a diverted trip (or both?). What about a cappuccino?

If the need for java hit as you approached the site, and you turned right in, this would be a standard diversion. But since you passed the driveway and turned around, ….you need to take public transit and stop burning up our resources.

Hey Mike, After you do trip gen. calcs (let’s say for a built-up year 2029) but you want to consider design year (typical 20 years) and you want to design/improve nearby roads for the design year 2049 (2029 + 20 years); do you apply same growth rate on trip generated as you would do for existing traffic? or you apply the growth rate on existing traffic, and use trip gen numbers without applying a growth rate?

No – the growth rate is not applied to the trip generation. For instance, the trips generated by a single family home isn’t going to keep growing over time. They’re assumed to be static.

My mission is to help traffic engineers, transportation planners, and other transportation professionals improve our world.

Get these blog posts sent to your email! Sign up below.  

Session expired

Please log in again. The login page will open in a new tab. After logging in you can close it and return to this page.

Get our information in your Inbox!

Sign up below to stay informed

• View Record

TRID the TRIS and ITRD database

Trip Generation Manual, 10th Edition

The Trip Generation Manual, 10th Edition includes: (1) Volume 1, Desk Reference: Provides a detailed description of new urban and person-based trip data, key instructional information, sample plots, and identifies significant changes from the previous edition. (2) Volume 2, Land Use Data Plots: Includes a complete set of land use descriptions and plots for all land use/time period/independent variable combinations. The electronic version of volume 2 is available in its entirety or via 3 individual land use packages: Land Use Package 1: Residential, Lodging, Recreational; Land Use Package 2: Port/Terminal, Industrial, Institutional, Medical Office; and Land Use Package 3: Retail, Services. The print version is available as a 3,000 page document. (3) Trip Generation Handbook, 3rd Edition: Provides new guidance on proper techniques for estimating person and vehicular trip generation rates; updates guidance for the evaluation of mixed use developments and the establishment of local trip generation rates; and expands pass-by trip and truck trip generation data. (4) ITETripGen Web-based App: Desktop application that allows electronic access to the entire trip generation dataset with numerous filtering capabilities of including site setting (i.e., rural, suburban, urban), geography, age of data, development size, and trip type (person or vehicular trips).

• Record URL: https://www.ite.org/technical-resources/topics/trip-and-parking-generation/trip-generation-10th-edition-formats/
• Find a library where document is available. Order URL: http://www.ite.org/tripgeneration/index.asp
• Supplement to 10th edition published 2020 is available at https://ecommerce.ite.org/IMIS/ItemDetail?iProductCode=TG10-SUPPELEC-E.

Institute of Transportation Engineers (ITE)

• Publication Date: 2017
• Media Type: Web
• Edition: 10th
• Features: Figures; Tables;

Subject/Index Terms

• TRT Terms: Data files ; Handbooks ; Land use ; Manuals ; Statistics ; Trip generation
• Geographic Terms: United States
• Subject Areas: Planning and Forecasting; Transportation (General);

Filing Info

• Accession Number: 01658601
• Record Type: Publication
• Files: TRIS
• Created Date: Jan 31 2018 10:50AM

Welcome to ITE’s Online Trip Generation Data Submission Site

Submit data for ite’s 10th edition trip generation manual by november 30th.

Help update, expand, and improve the ITE Trip Generation Manual. ITE relies on volunteer submittal of data to ensure delivery of the most accurate and up-to-date information available. Data for all land uses (including urban, suburban and vehicle or person trips) is being accepted. (For specific information on land use data requested, please click here )

After Registration, login to the application

Submit Data

Fill out data forms and submit to ITE.

Powered by TRANSOFT SOLUTIONS

Communities

All Member Forum

Councils and Commities

Member Created

CC and IBOD

All Communities

My Communities

Upcomming Events

Discussion post

Library Entities

Latest Blogs

Participate

Post a message

Share a File

Join a Community

ITE Trip Generation Data Submission Portal

Thank you for helping update, expand, and improve the ITE Trip Generation Manual . Data for all land uses and a variety of modes (vehicle, pedestrian, bicycle, truck, and transit) is being accepted. To submit data to ITE, please fill out the fields below. Note: Fields with an * are mandatory.

We're sorry, but to function, this form requires javascript be enabled.

Detailed description of study site, including characteristics that may not be apparent from standard site measurements. Observations about (1) the presence of transit or walk trips at the site and (2) the cost and supply of on-site parking would be helpful.

Please attach one (1) to three (3) files with relevant trip generation information here (e.g., Transportation Impact Analysis Report, spreadsheets with data counts, etc.). Accepted file types: .pdf .doc .docx .xls .xlsx and .csv. Maximum file size: 20-25MB.

If you prefer, hard copy submittals are also accepted using ITE's standard trip generation data collection form . You can complete the form and email it to [email protected] .

By submitting on this portal, you agree that you have read and will follow the following terms and conditions:

Do not submit any information or other material protected by copyright without the permission of the copyright owner. By posting material, the posting party warrants and represents that he or she owns the copyright with respect to such material or has received permission from the copyright owner. In addition, the porting party grants ITE the nonexclusive right and license to display, copy, publish, distribute, transmit, print, and use such information or other material.