The Next Generation of VMT Reduction Programs

EPA Grant Number: F6C40888
Title: The Next Generation of VMT Reduction Programs
Investigators: Bricka, Stacey G.
Institution: The University of Texas at Austin
EPA Project Officer: Cobbs-Green, Gladys M.
Project Period: September 1, 2006 through September 1, 2008
Project Amount: $106,896
RFA: STAR Graduate Fellowships (2006) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Economics and Decision Sciences , Fellowship - Urban and Regional Planning


Nationally, air quality improvement programs focus on commuters as the key venue for reducing vehicle miles of travel (VMT) and associated emissions. The current programs are employer-based with the employer marketing alternative modes of travel and providing financial and other incentives to those commuters stop driving alone. The realization of national VMT reduction goals through employer-based programs is thus contingent upon commuters having the flexibility to change their travel mode from drive alone to carpool, vanpool, or transit.

Recent changes in demographic, work, and travel characteristics suggest a decreased level of flexibility for some commuters. This is reflected in increased proportions of commuters driving alone and a corresponding increase in “trip chaining” or multi-purpose trip making as part of the work commute. The prevailing hypothesis is that increased trip chaining results from the increased proportion of mothers in the workforce, juggling home and work responsibilities.

The objective of this research is to identify factors that influence commuter trip chaining in order to identify the extent to which commuters have the flexibility to use alternative modes. Research questions include:

  1. What are the constraints that impact travel flexibility and how do they vary across family types?
  2. What does the mix of commuters, based on their family structure and corresponding constraints, tell us about the potential for saturation in employer-based VMT program results?
  3. For those commuters whose constraints prohibit them from participating in an employer-based VMT reduction program, what other programs can be designed that take into account these constraints but still contribute to VMT reduction goals?


This research will be conducted using both quantitative and qualitative techniques. First, using national travel survey data, I will empirically identify the factors that influence travel behavior during the work commute (particularly trip chaining), focusing primarily on demographic, work, and activity setting constraints. The result of this first effort will be a market segmentation of commuters, reflecting their levels of flexibility in participating in employer-based VMT reduction programs. Using those results, the qualitatively portion of my research will be a case study application: what proportion of commuters has the flexibility to change travel modes? For those who do not, what new programs might help to reduce their VMT?

Expected Results:

This research is structured to provide a clear delineation of factors that influence trip chaining, identify levels of flexibility in commuter travel, present a market segmentation of commuters in terms of their flexibility levels, and estimate the reach of current programs. This research will provide insight into the need for and possible structures of alternative, commuter-focused VMT reduction programs. It will explore the factors that influence trip chaining behavior, with explicit consideration of the role that gender and cultural expectations regarding the division of household responsibilities plays in constructing the commute trip.

Supplemental Keywords:

fellowship, household travel behavior, trip chaining, transportation, automobile use, market segmentation, VMT reduction programs,, RFA, Economic, Social, & Behavioral Science Research Program, Scientific Discipline, decision-making, Ecology and Ecosystems, Economics & Decision Making, Social Science, emission levels, commuting, barriers, business-led environmental management, decision making, environmental decision making, community participation, demographics, environmental policy, vehicle miles of travel (VMT), behavior change