Measuring Transportation Impacts Using Vehicle Miles Traveled (VMT)

Transportation impacts due to trucks and cars travelling through mountains on bridge spanning river

With the passage of Senate Bill 743 and official adoption of the measures into the 2018 California Environmental Quality Act (CEQA) Guidelines, transportation impacts will no longer be determined using level of service (LOS), a measure of traffic congestion. Rather, projects will be required to determine transportation impacts based on vehicle miles traveled (VMT). This standard goes into effect July 1, 2020, though some jurisdictions may adopt VMT analysis sooner.

Determining VMT

VMT is a measurement of distance travelled regardless of the number of passengers in the car. For land use projects, VMT must be analyzed per capita, per employee, and on a net basis. For transportation projects, lead agencies for roadway capacity projects have discretion, consistent with CEQA and planning requirements, to choose whether to evaluate transportation impacts on a per capita, per employee, or net VMT basis.

There are a number of methodology options available for calculating and estimating VMT, including travel demand models (trip or tour based models), sketch models (CalEEMod, Sketch 7, UrbanFootprint, MXD etc.), and spreadsheet models (VMT calculator or estimator); research into regional or local transportation plans and policies; and data (travel surveys such as California Household Travel Survey). Some cities, such as the City of Los Angeles have developed a VMT calculator tool, specifically designed to estimate project-specific VMT per capita and per employee, primarily for land use development projects. With this tool, vehicle trips and VMT generated by a development within the City of LA can be reviewed and the effect of transportation demand management strategies and mitigations can also be applied to determine the significance of impact per local criteria.

Mitigating Transportation Impacts

VMT mitigation focuses on fewer cars or fewer vehicle trips (i.e., not mitigating through roadway expansions etc.), meaning transit-oriented (TOD) development is becoming increasingly important, specifically infill development near transit. Mitigation measures may include pedestrian and bicycle infrastructure or network improvements, commute trip programs such as parking cash out, transit allowances, or flexible work schedules/telecommuting, which provide commuters incentives and resources to reduce their automobile travel; and shared mobility, that is transportation services and resources that are shared among users, either concurrently or one after another. Shared mobility options include taxis, carsharing, bikesharing, carpooling, vanpooling or shuttle services, and reduced parking to encourage transit usage. Notably, under VMT, mitigation is identified upfront but implementation is ongoing and can last over the project’s lifespan. Since VMT is a largely a regional impact, regional VMT-reduction programs may be an acceptable form of mitigation. In-lieu fee (ILF) programs would also be a valid mitigation where there is an evidence that mitigation will actually occur.

LOS’ Future

Highly urbanized areas, such as San Francisco, that have focused on infill and have “poor-performing” (according to LOS) intersections at most locations will find value in eliminating LOS as a metric. For these areas, elimination of LOS can save money, result in a focus on VMT reduction, and speed up the environmental review process for some projects that trigger LOS impacts due to their location in congested areas, which make mitigation via roadway/intersection improvements impossible. However, smaller cities that do not experience high levels of congestion may find that LOS still holds informational value, particularly to members of the community.

For example, the City of Pasadena’s thresholds include VMT and other metrics that consider effects on modes of travel not taken in single-occupancy vehicles. However, the City still includes LOS in the project evaluation process as a condition of approval for projects of communitywide significance. The conditions of approval for projects in Pasadena that decrease LOS include reducing vehicle trips rather than making operational improvements that increase capacity. Pasadena has found a new and interesting way of using the LOS metric, as congestion control is important to the community. This new approach allows the City to utilize LOS in accordance with the intent of SB 743, while still doing away with the CEQA triggers.

Eventually, there may be a total shift away from LOS as a measure of transportation impacts, but complete transformation may take longer than anticipated. Some cities, like Pasadena, may continue to use LOS as an indication of operational efficiency in the meantime. Additionally, LOS can and will still be used as a metric of congestion for construction traffic and access/circulation impacts.

For more information, contact Senior Transportation Project Manager Dennis Pascua.