1. EVALUATING THE TRANSPORTATION IMPACTS OF MULTIFAMILY HOUSING
Amanda Howell, Kristina Currans, &
Kelly J. Clifton, Ph.D.
TRB Planning Applications Conference
May 17, 2017

2. Introduction
Transportation impact analyses that rely on conventional data & methods may unduly burden development by overestimating automobile use.
Research has shown that trip generation methods are not sensitive to:
The urban context where development is located
Socio-economics of visitors to a site
Differentiation between land use types
This is particularly salient for affordable housing, as cities struggle to encourage more supply to deal with critical shortages across the US.

3. Study Goals Assess the transportation impacts of affordable housing
Vehicle ownership
Trip Generation
Income levels
Regional and local context
Use methods that can be compared to:
ITE’s trip generation methods
Person trip methodology
Inform land development process:
Transportation impact analysis
Parking supply

4. Research Approach Analyze household travel survey data
Examine the relationship between:
travel outcomes: (vehicle ownership, vehicle trips, person trips) &
independent variables (housing type, household size, income, location)
Negative binomial regressions (discrete count data)
Limited set of independent variables to compare against (conventional & new) trip generation data and methods

5. Data & Methods 2012 CA Household Travel Survey
2,431 households across all 58 counties in CA
Dwelling type: multifamily and single family
Matched income levels of households to those regionally- adjusted, income-qualifying limits set by CDHCD
Extremely Low-Income (ELI) – max income of 30% of AMI
Very Low-Income (VLI) – 31-50% AMI
Low-Income (LI) – 51-80% AMI
Area Median Income (AMI) – 100%
Moderate Income (MI) – % AMI
Above Moderate Income (all others in sample)
Control for local and regional context
Source: Govloop.com

6. Place Types
Quantified Caltrans Smart Mobility Framework (2010) to create 4 urban place types
EPA’s Smart Location Database
Census block group
Pop, emp. & intersection density
% single family homes
Transit & automobile accessibility
Urban place types:
- Suburban Neighborhood
- Urban Neighborhood
- Urban District
Urban Core

7. Results
Estimates and graphics were developed controlling for contexts in San Francisco and Los Angeles
Predicted values are for 4-person households on average weekdays.
BETA, coefficient: For a unit change in the variable, the difference in the logs of expected counts. 
EXP(BETA) provide the magnitude difference for the given coefficient. 
An exp(beta) of 1.5 means observations with that variable are 1.5 times the higher than the base case. 
If beta is not significantly different from 0, exp(beta) ~ 1... no significant change in magnitude.

8. No. of HH Vehicles Owned by Multi-Family Residents
Auto ownership in SF is 81% that off everywhere else, on average. 

9. Home-based Vehicle Trips for Multifamily Residents
Home-based vehicle trip rates in SF are 77% (23%) for all place types than the rates in all other locations, except LA.
Home-based vehicle trip rates in LA across place types are significantly different than the average rates observed elsewhere. 
LA, non-urban: rates are 94% the average rages observed everywhere else (so people make fewer HBVT in non-urban LA)
LA, suburban and urban neighborhood: rates are 1.01 times higher than average suburban and urban neighborhood rates.
LA, urban district: rates are 1.10 times higher than average urban district rates.
LA, urban core : rates are 1.53 times higher (~50% more) than average urban core rates elsewhere (which mostly just includes SF).

10. ITE Residential Apartment (LUC 220) Weekday Demand Compared to Caltrans Data
ITE's average rate is 6.47 VT/DU (suburban, LUC 220, general apartment, assuming average median income)
Estimated rates for income, as plotted
ELI: 3.54 VT/DU
VLI: 4.58 VT/DU
LI: 5.51 VT/DU
MOD: 5.93 VT/DU

11. Home-based Person Trips for Multi-Family Residents

12. Conclusions
Significant differences in the travel outcomes across income categories
Reinforces the role of the built environment associations with automobile ownership and use
Fewer vehicle trips with increasing urban residential location
Comparison to ITE’s vehicle trip rate for multifamily shows the degree of overestimation when income is not considered
Differences in person trips are less dramatic (only urban/suburban dichotomy)
Punctuates the need for more information in the analysis process

13. Next steps Mailout survey residents of 100 affordable sites in LA & SF
Including those 20 on-site collection locations
Stratified by land use type
On-site vehicle and person trip counts using 3rd edition of the ITE Handbook)
20 affordable sites in SF & LA regions
Stratified by place type
Data Source
Demo-graphics
Trip Generation
VMT
TDM
Mode
Use
Person
Counts
Vehicle Counts
Parking
Vehicle Ownership
On-site
Intercept X
Mail-Out Survey
CA 2012 HTS

14. Questions?
Kelly J. Clifton

15. appendix

16. Negative Binomial Regression Model Estimates for Vehicle Ownership

17. Negative Binomial Regression Model Estimates for HBPT and HBVT