Vehicle Miles Traveled

VMT refers to the total number of miles driven on roadways in a defined area during a defined period. Regional VMT is influenced by a complex set of interconnected factors. At the macro level, higher unemployment, higher fuel prices, increased congestion, telework programs, employer carpool programs, and concentration of development in centers are all linked to VMT reduction. Increasing access to transit services and access to bicycle and pedestrian facilities can also reduce VMT. On the other hand, population growth, higher household income, increased fuel economy and greater roadway capacity can all be linked to increasing VMT.  

VMT in the Tahoe Region is thought to be a function of a complex interplay of a variety of factors including population (both inside and outside the Region), visitation rates, gas prices, employment rates, local housing costs, demand and access for recreational opportunities in the Region, and access to alternative forms of transportation. 

The understanding of the relationship between in-region nitrogen (NOx) emissions and atmospheric deposition has progressed as a result of empirical observations over the last 30 years.  

•    Current in-basin NOx emissions from mobile sources are substantially below 1981 levels despite varying VMT values.
•    A 14-fold increase in VMT from 1981 levels would be required to equal the 1981 NOx emissions levels.
•    The goal established by the VMT standard, a 10% reduction in NOx emissions from in-basin mobile source, was likely achieved more than 15 years ago.
•    NOx emissions are likely to continue to decline further as a result of increasingly strict tailpipe emissions standards.
•    Atmospheric deposition of nitrogen hasn’t changed significantly in the last 20 years.
•    Nitrogen emissions from mobile sources in the Region have declined by more than 66 percent, far in exceedance of the standard’s goals. Despite this decline, no significant change in atmospheric deposition of nitrogen has been observed.

This project is urgently needed to support the TRPA threshold update process and to inform the regional transportation program. The states of California and Nevada convened a regional Bi-State consultation group that brought together high-level decision makers from both states to address the region’s transportation challenges. Consistent with both the Regional Plan and Regional Transportation goals of reducing reliance on the private automobile, the Bi-State coalition established a goal of increasing non-auto mode share in Tahoe by 5% by 2028. The group is working to define policies, projects, and funding mechanisms to achieve this ambitious goal.

This VMT assessment project will provide the Bi-State consultation group with a better understanding of the factors that have influenced VMT and traffic volume changes in the past, and those that are expected to drive traffic patterns in the future. The Bi-State group is set to reconvene in the coming year to advance regional transportation goals. To best support Bi-State consultation discussions and efficiently leverage Regional Transportation Plan update efforts, this work must be complete by March 2021.  

Contact for more information: Alison Toy; natoy@ucdavis.edu

Related Documents:

DRI WO5 – Vehicle Miles Traveled Review

“Final report: Vehicle Miles Traveled Review”

Prepared for the Tahoe Science Advisory Council Threshold Update 2017-18

By John Mejia, Eric Wilcox, Sandra Rayne and Ehsan Mosadegh, July 2018, Revised, March 2019