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, citywide). 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. Final assignment origin-destination (OD) trip tables or production (P) and attraction (A) estimates multiplied by distance skims may be used. 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 the work location and the return to home).

The allocation of responsibility within a jurisdiction is straightforward, since each trip is attached to a worker. However, 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.

This is similar to Total VMT per Service Population.

Total VMT per Service Population
This uses the same method as Total VMT Generated by a Project to estimate VMT and then divides 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 those variables are included 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 that 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 straightforward, 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-home-based trips.

This is not applicable for trip-based models, since non-home-based (NHB) trips aren’t tied to the households making them.

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

The allocation of responsibility within a jurisdiction (e.g., cities within a county) is straightforward, since each trip is attached to a resident and each resident has a single home location.

Household size determination is required, 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.

Residential VMT per household is a related metric: the 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 the 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 straightforward, except for work-based 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

Fehr & Peers Suggested Guidance for Induced Vehicle Travel Impact Analysis, January 2022

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, we have partnered with over 350 public agencies in California, ranging from the state’s largest cities to rural counties, to develop VMT impact analysis procedures. We understand that each community faces unique challenges and opportunities. The examples below demonstrate 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

 

Outlining VMT metrics for quick assessment of transportation impacts in a webinar

VMT Reduction Through TDM

Latest TDM Research

VMT Mitigation Programs

 

Model Criteria Checklist

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