1. Auto Ownership Model For Southeast Florida Models Southeast Florida FSUTMS Users Group Meeting Ft. Lauderdale, FL
May 16, 2008
Corradino

2. Why? Life Style Gen Requires Number of HHs Current model input is:
At each auto ownership level (0, 1, 2, 3+)
For HH with and HH without children
Current model input is:
Vehicles in HH’s with children
Vehicles in HH’s without children
Disaggregated by a series of polynomials
Lack of consistent and logical forecasting methodology
Most models either grow vehicles in proportion to HH’s, or
Perhaps adjust to meet county aggregate total
May 16, 2008
Corradino

3. Past Work For District 4 – Paper by Li, Ewing & Gross (late 1990’s?).
Other major urbanized areas throughout the US.
Encouraged by USDOT
Most models use some combination of:
Persons
Workers
Density
Children
Income – Almost all require this one ****
Accessibility
May 16, 2008
Corradino

4. Since FSUTMS Doesn’t Use Income and Previous Work Required Income
Persons/HH
Workers/HH
Children
With
Without
Density (HH, Emp, Area)
Accessibility (Time & Trip Attractions)
May 16, 2008
Corradino

5. Model Form Multinomial Logit
Sx = Exp(ux)/[Exp(u0)+ Exp(u1)+ Exp(u2)+ Exp(u3)]
Where
Sx = share of HH’s at each auto ownership level (0,1,2,3)
ux = utility for level x
= f(persons or workers/HH, density, accessibility)
May 16, 2008
Corradino

6. Density Calculation
Density = (Households + Total Employment)/(net area)
May 16, 2008
Corradino

7. Accessibility Calculation
Inputs
Travel Time Skim Matrix (for GM)
Trip Attractions (from “trial” Gen run)
Friction factors
For each TAZ:
Accessibility=
Sum of: FF(t)*Attractions for each purpose
Over all destinations
May 16, 2008
Corradino

8. Best Model Households without children Rho-squared: 0.342683 Persons
Density
Accessibility
Rho-squared:
May 16, 2008
Corradino

9. Best Model Households with children Rho-squared: 0.288637 Workers
Density
Accessibility
Rho-squared:
May 16, 2008
Corradino

10. Other Notes
Gross and Ewing found a rho-squared of for their model 4.
For the 0, 1, 2+ models, comparable to Gross and Ewing, our models have rho-squared of 0.39 and 0.50 for without and with children respectively. These models are at least as well as Gross and Ewing.
For the 0, 1, 2, and 3+ models, the proposed models have rho-squared of 0.34 and 0.29 for without and with children respectively. These are still good models, but as expected, the task is more difficult when trying to estimate 4 levels.
The signs in all models are correct, and all variables included in the equations are significant at the 0.05 level and beyond for most variables.
May 16, 2008
Corradino

11. Remaining Work County Biases will be tested
Life-Style Gen will have to be modified to use the new model
Actual model implemented in Matrix
May 16, 2008
Corradino

12. Questions?
May 16, 2008
Corradino