|
|
|
| Why Trip Generation Matters? |
| |
|
|
|
A frequent barrier to infill, affordable housing
is the result of a Traffic Impact Analysis. Traffic Impact Analyses assume
that new land uses will generate a certain amount of local vehicle
trips. Those trips are added to existing local traffic conditions in
a simulation. If the simulation results in a projected degrading of
the Level of Service of local streets, a development may be forced to be
scaled down. |
| |
|
|
| What are the problems? |
| |
|
|
|
Unfortunately, the trip generation rates used in
Traffic Impact Analyses are often simplistic, inaccurate, and
statistically unreliable. Trip generation rates rarely take into
account access to transit, neighborhood density and demographic factors
like income and age (for more, see Shoup, Truth in Transportation
Planning). |
| |
|
|
| Purpose of This Page |
This page provides some data on trip generation
to help planners and develpers engage more effectively in discussions on
traffic impacts of infill developments. |
| |
|
|
| Important Associations to Consider |
|
a. Vehicle Ownership and Trip Generation |
|
b. Income and Trip Generation |
|
c. Age and Trip Generation |
|
|
|
|
|
| |
a. Vehicle Ownership and Trip Generation |
| |
|
|
|
Observation |
Trip generation rates are lower
for households who own fewer vehicles. |
| |
|
|
|
Implication |
Traffic Impact Analyses should
consider factors in a housing development that impact vehicle ownership
including: income, age, disability, density, transit access, parking
constraints, parking prices, and unbundled parking. |
| |
|
|
|
Data and Facts |
|
|
|
Trip Rates by Vehicle are typically one-third
higher for households with 2+ vehicles than 1-vehicle households which are
two-thirds higher than 0-vehicle households. (Ewing) |
| |
|
|
|
|
Table:
Bay Area Household Weekday Trips Per Day by Household Size and Vehicles
Available |
|
|
|
Vehicles per Household |
|
|
|
0 |
1 |
2 |
3+ |
|
|
1 person HH |
2.72 |
3.91 |
3.81 |
4.17 |
|
|
2 person HH |
4.05 |
5.79 |
6.71 |
7.08 |
|
|
3 person HH |
5.78 |
7.30 |
8.37 |
9.64 |
|
|
4 person HH |
6.46 |
9.36 |
11.08 |
12.68 |
|
|
Source:
San Francisco
Bay Area 1990 Regional Travel Characteristics: Working Paper #4 |
| |
|
|
|
|
|
|
|
b. Income and Trip Generation |
| |
|
|
|
|
|
|
|
Observation |
Trip generation rates are lower for lower income households,
and a higher percentage of those trips are via transit. |
| |
|
|
|
|
|
|
|
Implication |
Traffic impact analyses should
reflect the lower traffic impact created by affordable housing
developments compared to other land uses including market rate housing. |
| |
|
|
|
|
|
|
|
Data and Facts |
|
|
|
|
|
|
|
Table:
Bay Area Household Weekday Trips Per Day per Household Size by Income |
|
|
|
Total
Trips |
Percent
Transit |
|
|
Low Income (<
$25,000) |
5.5 |
12.5% |
|
|
Low
Medium Income ($25,000 - $45,000) |
7.5 |
5.8% |
|
|
High Medium Income
($45,000 - $75,000) |
9.4 |
4.6% |
|
|
High Income (>
$75,000) |
10.5 |
3.7% |
|
|
All Households |
7.6 |
6.6% |
|
|
Source: San Francisco
Bay Area 1990 Regional Travel Characteristics: Working Paper #4 |
| |
|
|
c. Age and Trip Generation |
| |
|
|
|
|
|
|
|
Observation |
Trip generation rates are lower for
senior households, and a higher percentage of those trips are via transit. |
| |
|
|
|
|
|
|
|
Implication |
Traffic impact analyses should
reflect the lower traffic impact created by senior housing developments
compared to other land uses including market rate housing. |
| |
|
|
|
|
|
|
|
Data and Facts |
|
|
|
|
|
|
|
Table:
Bay Area Trips per Household by Household Life Cycle Category |
|
|
Household
Life Cycle Category |
Trips
per Day |
|
|
Single Adult,
Retired, No Children |
2.7 |
|
|
Two
or More Adults, Retired, no Children |
6.2 |
|
|
Average for All
Households |
7.6 |
|
|
Source: San Francisco
Bay Area 1990 Regional Travel Characteristics: Working Paper #4 |
| |
|
|
|
|
Table:
Bay Area Trips per Person by Age Group |
|
|
Age
Group |
Trips
per Person |
%
Transit, Walk, Bike |
|
|
5-17 |
2.6 |
29.2% |
|
|
18-22 |
3.1 |
18.6% |
|
|
23-29 |
3.1 |
17.6% |
|
|
30-39 |
3.6 |
14.7% |
|
|
40-49 |
3.7 |
13.3% |
|
|
50-59 |
3.4 |
15.1% |
|
|
60-64 |
2.9 |
14.7% |
|
|
65 + |
2.5 |
19.1% |
|
|
Source: San Francisco
Bay Area 1990 Regional Travel Characteristics: Working Paper #4 |
| |
|
|
|
|
|
|
Ewing, Reid and Shi-Chiang Li. 1998. A Vehicle Ownership Model for FSUTMS.
Washington, D.C.: National Research Council, Transportation Research Board.
Purvis, Charles L. 1994. San Francisco Bay Area 1990 Regional Travel
Characteristics: Working Paper #4. Metropolitan Transportation Commission:
Oakland, Calif. Available at: http://ntl.bts.gov/DOCS/SF.html
(Visited April 1, 2001).
Shoup, Donald C. 2000. Truth in Transportation Planning. Washington, D.C.:
National Research Council, Transportation Research Board.
