A new tool to quantify the traffic reduction
benefits of New Urbanist, transit-oriented and infill
development projects
Traffic studies are at the heart of many fundamental
decisions on land use, street design and urban form.
By analyzing the number of trips expected from a new
development, and the consequent impact on traffic
congestion at neighboring intersections, the traffic
study is a driving force behind roadway widths, street
and intersection design, and the level of fees that
a developer must pay to upgrade the transportation
infrastructure.
The Institute for Traffic Engineers' (ITE's) Trip
Generation report and the companion Trip Generation
Handbook are the most definitive available sources
for estimating the automobile traffic that different
land uses will generate. However, the information
is most useful for auto-oriented, stand-alone suburban
sites, from where the vast majority of data were collected.
For downtowns or areas with good public transportation,
ITE advises that traffic engineers should collect
local data, or adjust the ITE average trip generation
rate to account for reduced auto use.
All too often, however, ITE's warnings are ignored
and standard trip generation rates are applied in
inappropriate locations - with serious impacts on
the character and financial feasibility of urban development.
Part of the reason is that, until now, there has been
no standardized tool to allow these adjustments to
trip generation rates to be made. In order to address
this problem, the air quality management districts
of California, along with the California State Department
of Transportation, worked together in 2004 to examine
all of the key variables that influence automobile
trip generation. They were able to quantify the trip
generation impact of key locational and programmatic
factors, and inserted these formulas into URBEMIS,
a national model for calculating air quality impacts
of projects.
The URBEMIS mitigation component, developed by Nelson\Nygaard,
is a simple yet powerful tool; it employs standard
traffic engineering methodologies, but provides the
opportunity to adjust ITE average rates to quantify
the impact of a development's location, physical characteristics
and any demand management programs. In this way, it
provides an opportunity to fairly evaluate developments
that minimize their transportation impact, for example,
through locating close to transit or providing high
densities and a mix of uses.
Download the full report
(pdf less than 1 MB)
