Overview

Current practices throughout California, and nationwide, focus on establishing level of service (LOS) standards – typically based on automobile delay at signalized intersections. The ATG approach, by contrast, is based on the premise that each net new vehicle trip generated by a project constitutes an incremental impact to the transportation network and thus requires mitigation. As a result, ATG provides a more direct connection between a project’s environmental impacts and mitigation, and serves as an easily-measured proxy for LOS impacts to pedestrians, bicycles, transit, and automobiles.

Benefits for Measuring Impacts and Mitigation

ATG is better than other methodologies at linking impacts to mitigations. This is especially true for environmental impacts like greenhouse gas emissions and for proposed mitigations that would improve bicycle and pedestrian networks. ATG can also be useful when estimating the impacts of project-generated vehicle trips in already-congested corridors. In the City of West Hollywood, for example, existing levels of peak-period congestion make it difficult to determine the incremental impacts of a project on congestion. In the event that an impact is identified, there are limited opportunities for making physical improvements in the street system to mitigate traffic congestion, because the City is already built out. Since mitigations to improve auto LOS are generally infeasible, it may be more appropriate to measure project-generated impacts by determining auto trips generated. Fees collected as mitigation could then be used to improve facilities for pedestrians, bicyclists and transit users (funds can already be used to improve vehicular operations).

Benefits to the Built Environment

Cities can include built environment factors, (such as widened sidewalks, curb extensions, separated bicycle facilities and transit stop enhancements) when developing mitigation measures for auto trips generated.

Table 1: Relative Performance of LOS and ATG as measures of

environmental impacts. From SFCTA, “Automobile Trips Generated:

CEQA Impact Measure and Mitigation Program,” 2008

ATG Nexus Fee Study

ATG can also be tied to developer impact fees, which could be used to pay for new or improved pedestrian, bicycle or transit infrastructure. A nexus fee study would establish the connection between new development and the need for new or expanded transportation facilities. After establishing the nexus, the study would be charged with calculating development impact fees to be levied for each land use on a per auto trip basis. The fee would be charged based on automobile trips and used to reduce automobile trips, which would establish an essential nexus between fee collection and fee usage.

How to Measure

Existing applications of ATG generally use vehicle trip generation published in ITE’s Trip Generation. Alternative rates for vehicle trip generation may also be used, where locally appropriate.

Auto Trips Generated (ATG)

Multi-Modal Level of Service Toolkit

Potential Applications

Development review General Plans Congestion Management Plans

Sample Applications

Impact Fee Policies

The City of Palo Alto bases its traffic impact fee on

additional vehicle trips generated, which are estimated

using ITE’s Trip Generation. Small retail

establishments, public schools and childcare facilities,

and affordable/below market rate housing are all

exempt from the traffic impact fee.

General Plan Updates

In 2010 Fehr and Peers provided guidance to the City

of West Hollywood for the adoption of an ATG

standard as part of their Mobility Element update.

Shifting to ATG would help the City achieve its goals

for improved pedestrian and bicycle facilities and GHG

reduction by linking each new auto trip to mitigations.

Environmental Impact Analysis

The City and County of San Francisco have also

investigated shifting to an ATG standard for

environmental impact analysis and impact fee

standards. A nexus study for the impact fee was

released in March, 2012, and San Francisco is

currently seeking bids for an EIR of the new standard.

Data Requirements

Type of land use: retail, office or more specific (use with ITE trip generation standards)

Potential mitigations and their estimated trip reductions

Figure 1: Impact determination process using ATG standard.

From SFCTA, “Automobile Trips Generated: CEQA Impact Measure

and Mitigation Program, 2008.

Advantages

Better at evaluating environmental impacts than traditional auto LOS measures

Good at linking transportation impacts to impact mitigation

Simpler to measure than auto LOS

More meaningful than LOS in congested conditions

Disadvantages

Does not evaluate street design

Does not evaluate trade-offs between different modes (pedestrian vs. auto, transit vs. bicycle, etc.)