VMT: Going Beyond LOS

Why vehicle miles traveled (VMT) is becoming a preferred metric for transportation impact analysis

EXAMINE

Level of Service

Analyze the benefits, limitations, and blind spots of Level of Service (LOS) analysis.

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EXPLORE

VMT Explained

Understand vehicle miles traveled and the potential impacts of this analysis.

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ACT

Next Steps

Determine whether making a shift from LOS to VMT will benefit your community. 

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Incorporating VMT into transportation impact analysis is a transformative change that shifts the focus from measuring impacts to drivers to measuring the impact of driving. VMT helps describe the environmental consequences of land use and transportation network decisions while LOS describes traffic operations effects. Communities long focused on single locations and the delay experienced by people in cars are shifting gears to look at network wide efficiency and the experience of all people traveling.

Exhibit 12-14 LOS Examples for Basic Freeway Segments

Source: 2016. Highway Capacity Manual 6th Edition: A Guide for Multimodal Mobility Analysis. Washington, DC: The National Academies Press. https://doi.org/10.17226/24798.

Examining Level of Service

LOS relies on letter grades, much like a report card, to describe the comfort and convenience of driving from a driver’s perspective. While getting a good LOS grade (e.g., LOS A-C) may be desirable to drivers, it represents inefficient use of public space, not to mention a variety of other adverse environmental effects as documented in the research below.

Limitations of LOS as an Environmental Impact Metric

    Source: California Governor’s Office of Planning and Research, Transportation Impacts (SB 743) https://opr.ca.gov/ceqa/updates/sb-743/

    Expanding impact analysis metrics to include VMT can help provide a more complete perspective of the potential effects of land use and transportation decisions.

    LOS Versus VMT: Measurement Matrix

    The following measurements and considerations are used with each metric:
    LOS
    Q

    Emissions (Greenhouse Gases)

    Q

    Emissions (Air Pollutants)

    Q

    Fuel Consumption

    Q

    Energy Consumption

    Driver Delay (Speed)

    Driver Delay (Intersection Wait Time)

    Safety (Speed)

    Q

    Safety (Collisions)

    VMT

    Emissions (Greenhouse Gases)

    Emissions (Air Pollutants)

    Fuel Consumption

    Energy Consumption

    Q

    Driver Delay (Speed)

    Q

    Driver Delay (Intersection Wait Time)

    Q

    Safety (Speed)

    Safety (Collisions)

    Exploring VMT

    Rather than a letter grade, VMT measures the number of miles traveled by vehicles. The video below illustrates the components of VMT. 

    VMT Environmental Equivalencies

    VMT provides direct equivalencies for other environmental effects, such as emissions and energy consumption. It is also an indicator for safety because areas with low VMT generation rates have less frequent and less severe collisions.

    The following measurements are equivalent to 1 additional VMT:

    Pounds of Greenhouse Gas Emissions (GHG)

    Gallons of Gasoline (Energy Consumption)

    VMT as a Metric

    VMT metrics can take many forms depending on the type of project or impact analysis. Some of the more common forms are explained in the lexicon below.

    Total VMT

    All vehicle-trips (i.e., passenger and commercial vehicles) assigned on the network within a specific geographic boundary (i.e., model-wide, region-wide, city-wide). Vehicle volume on each link is multiplied by link distance.

    Total VMT Generated by a Project

    All vehicle-trips are traced to the zone or zones of study. This includes internal to internal (II), internal to external (IX), and external to internal (XI) trips. May use final assignment origin-destination (OD) trip tables or production (P) and attraction (A) estimates multiplied by distance skims. When the model has multiple assignment periods, OD trip tables and congested skims from each period should be used.

    Total VMT per Employee

    All automobile vehicle-trips made by employed persons are traced back to the workplace of the trip-maker, even trips that aren’t part of the work tour (i.e., all trips from home to work location and the return to home).

    Allocation of responsibility within a jurisdiction is straight-forward, since each trip is attached to a worker. But if some workers have multiple work locations then deciding which to count may be an issue.

    Commercial vehicle trips are not included.

    Home-Based VMT per Resident

    All home-based automobile vehicle trips are traced back to the residence of the trip-maker; non-home-based trips are excluded.

    Similar to Total VMT per Service Population.

    Total VMT per Service Population

    Same method as Total VMT Generated by a Project to estimate VMT and then divide by the population and employment of the zone or zones of study. If the model generates vehicle trips from other sources such as students and visitors, then include those variables in the service population. Note that employment is often used as the independent variable for total vehicle trip generation associated with non-residential land uses. This means that vehicle trips made by people other than the employees are accounted for in the trip rate including visitors, customers, vendors, custodians, and delivery companies. For this reason, it is often difficult to draw conclusions about VMT patterns and use of the metric should be limited to analysis scenarios comparing full model runs typically focused on changes at the sub-regional, city, county, or regional scale.

    Some trip-based models may not use population and employment as trip generation variables.
    Instead, they will rely on land uses. A ‘correspondence’ between the model land use input variables and population and employment rates is required for these types of models.

    Work Tour VMT per Employee

    All automobile trips which are part of home-work tours or work-based tours are counted. Intermediate stops along the tour between home and work locations should not be used to truncate the total home-work tour distance.

    Allocation of responsibility within a jurisdiction is straight-forward, since each tour or half-tour should be attached to a specific workplace.

    Commercial vehicle trips are not included.

    Residential VMT per Resident

    All automobile (i.e., passenger cars and light-duty trucks) vehicle-trips are traced back to the residence of the trip-maker, even non-homebased trips.

    Not applicable for trip-based models since nonhome-based (NHB) trips aren’t tied to the households making them.

    Can be calculated either by averaging the daily VMT of all residents or by calculating total VMT, counting total residents, and dividing.

    Allocation of responsibility within a jurisdiction (e.g., cities within a county) is straight-forward, since each trip is attached to a resident and each resident has a single home location.

    Requires household size determination, which can be subject to debate for different housing types (i.e., single-family, multi-family, and age qualified housing products).

    Commercial vehicle trips are not included.

    A related metric is residential VMT per household – denominator is the total number of households instead of the total number of residents. The benefit of this metric form is that it doesn’t require an estimate of household size.

    Total VMT per Land Use Unit

    All vehicle trips are traced to the zone or zones of study. This includes internal to internal (II), internal to external (IX), and external to internal (XI) trips. Use trip estimates or trip tables multiplied by distance skims similar to total VMT generated by a project.

    Home-Based Work (HBW) VMT

    All automobile trips between home and work are counted. (A variant might also count work-based
    other trips.)

    Allocation of responsibility within a jurisdiction should be straight-forward except for workbased other trips from one work location to another; even in this case it should be possible to decide which to count.

    Commercial vehicle trips are not included.

    VMT Analysis for Land Use vs Transportation Projects

    While efficiency metrics are most useful for land use project analysis, the expansion of roadways usually focuses just on the change to total VMT. The total VMT attributable to widening or building new roadways is known as induced vehicle travel effects. A variety of resources are available to explain the methodologies available to quantify induced VMT impacts.

    “Closing the Induced Vehicle Travel Gap Between Research and Practice,” Transportation Research Record:  Journal of the Transportation Research Board, Issue No. 2653, 2017

    Shifting from LOS

    California was the first state to mandate the use of VMT as the preferred metric for environmental impacts to the transportation system. Because of the important connection between VMT and greenhouse gas (GHG)/air pollutant emissions, safety, energy consumption, and land use efficiency, public agencies in other states such as Maryland, Oregon, Virginia, and Washington are now investigating VMT impact applications.

    So far, Fehr & Peers has helped over 350 public agencies in California develop VMT impact analysis procedures ranging from the state’s largest cities to rural counties. We understand that each community faces unique challenges and opportunities. Below are examples of how agencies in different land use contexts are approaching VMT impact analysis.   

    Urban

    City of Los Angeles (LADOT)

    City of San Francisco

    City of San Jose

    Suburban

    Butte County (BCAG)

    Placer County

    Western Riverside (WRCOG)

    Rural

    Mendocino County

    Tahoe (TRPA)

    Client Perspectives

    Fehr & Peers partners with leading agencies from across the country, providing LOS and VMT guidance, training, and custom implementation tools and strategies.

    “Consistent with the progressive direction of major planning initiatives recently undertaken by Montgomery County, Vehicle Miles Traveled per Capita is now one of the key transportation system performance measures used by County planners to evaluate the transportation adequacy of long-range master plans/sector plans.”

    Eric S. Graye, AICP, PTP

    Planning Supervisor, Montgomery County Planning Department

    “WRCOG could not be more pleased with the work that Fehr & Peers performed for us related to [VMT]. They did an excellent job of communicating a complicated subject to our Board members and other key stakeholders.”

    Christopher Gray

    Planning Director, Western Riverside Council of Governments (WRCOG)

    “The Fairfax County Department of Transportation (FCDOT) is evaluating Vehicle Miles Traveled (VMT) as a future measure for various types of analyses. We appreciate Fehr & Peers’ assistance in providing training sessions related to their experiences with VMT, from both the calculation and implementation sides of the process.”

    Gregg L. Steverson, PE, PTOE

    Deputy Director, Fairfax County Department of Transportation (FCDOT)

    Further Guidance

    At Fehr & Peers, we recognize how different these new provisions are from conventional approaches, and we know the transition can be challenging. To outline critical steps and choices for agencies, we developed the resources below. Let us help with breaking down the complexity and planning the path to conversion.

    Agency Choices

    Summarizing public agency decisions, options, and recommendations related to VMT.

    Replacing LOS with VMT

    Navigating the evolutionary change from LOS to VMT, the California story.

    New VMT Metrics

    Webinar outlining VMT metrics for quick assessment of transportation impacts.

    VMT Reduction Through TDM

    Latest TDM Research

    VMT Mitigation Programs

    Partner with us today on your community’s customized vehicle miles traveled approach.