Transportation Demand Management (TDM) aims to reduce private automobile trips, impacts on the transportation system, air quality, energy use, and travel costs while still preserving mobility options. However, obtaining reliable, usable data to evaluate real-world effectiveness of TDM strategies is a challenge. We are helping bridge that gap with our quick-response TDM+ tool.

TDM+ allows employers and developers to estimate how a Transportation Demand Management plan affects vehicle trip generation and corresponding vehicle miles traveled (VMT). Providing estimates ranging from conservative (for use in calculating VMT mitigations under new CEQA thresholds) to ambitious (for employers or clients willing to make a large investment in TDM and transportation programs), TDM+ quantifies TDM effects in less time and for a more refined geographic scale than other available models. It also relies on the most up-to-date available research based on a comprehensive literature review conducted in 2018. The tool’s versatility and depth enables it to address TDM questions for an individual development site up to a neighborhood level, such as:


What would be the effect on vehicle usage if we design our project to increase accessibility by transit and bicycles?


What potential ranges of effectiveness will we see from a specific combination of programs?


How confident are we that a robust TDM program can reduce traffic impacts or VMT impacts to a less-than-significant level?


Can we satisfy our jurisdiction’s vehicle trip-reduction policy by offering transit passes to our employees, or should we also institute a carpool matching program?


How might employee trips be different from visitor trips? Can we identify strategies that serve each of those populations?

TDM+ can also be customized for individual cities, tailored to capture the measures that matter most to local residents, developers, and city staff. Custom tools have been developed for an array of communities from San Jose, California to Aspen, Colorado, to Washington, D.C. San Jose currently uses a variant of TDM+ for assessing VMT impacts of all new development.

Developing TDM+

Our approach to analyzing TDM strategies includes a realistic, evidence-based assessment of how similar strategies have worked in similar locations. By incorporating nuances such as the urban form and limiting the measures included to those with well-documented research, the TDM+ approach allows for the highest level of technical rigor and defensibility when quantifying a program’s potential to reduce vehicle trips or vehicle miles.

This quantitative approach emerged from a 2010 partnership with the California Air Pollution Control Officers Association (CAPCOA) to develop a groundbreaking and comprehensive set of guidelines for assessing and quantifying reductions in vehicle miles traveled and greenhouse gas (GHG) emissions associated with more than 50 TDM strategies, both individually and in combination. Strategies covered a wide range of measures, from increasing transit frequency to implementing road pricing to encouraging location-efficient land uses, as well as more traditional TDM measures like ride-sharing programs and parking cash-out. Working with the Bay Area Air Quality Management District, the evaluation methods were validated by comparing the strategies to the San Francisco Bay Area.

Since the initial report was published, we have partnered with clients such as US EPA, California Air Resources Board, American Public Transit Association, California Housing and Community Development Department, and Urban Land Institute to continue developing and validating these methods, resulting in state-of-the-practice methods for estimating how TDM strategies affect travel behavior. The most recent iteration of TDM+ incorporates information from new studies published between 2010 and 2018, and will continue to reflect the most recent research in the field of travel behavior and TDM programs.

Case Studies

Transportation Demand Management Legislation, City of San Francisco

In February 2017, the City of San Francisco approved an ordinance establishing a TDM Program. This program requires developments to provide on-site amenities that support walking, bicycling, and transit, and reduce single-occupancy driving trips associated with a new development. In discussions with the City about ways to quantify effective measures to reduce trips, we shared the TDM+ tool to serve as a guide for how a city can create and implement their own customized tool.

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Zero-Carbon Buildings Feasibility Study, California Air Resources Board

As part of a research team led by UC Berkeley’s Center for Resource-Efficient Communities, we’re currently developing a study of building-scale transportation management strategies as part of the California Air Resources Board’s Zero-Carbon Buildings Feasibility Study. We’re reviewing new research on carbon emission reductions due to changes in the built environment and implementing TDM. After conducting a comprehensive inventory of transportation strategies, we’ll model the effectiveness of these strategies at reducing carbon emissions over time. This analysis will inform the emissions targets set by the California Air Resources Board for zero-carbon buildings in California.

VMT-Based Impact Thresholds and Analysis Guidelines, City of Los Angeles

We’re currently working with the City of Los Angeles to develop VMT-based impact thresholds and analysis guidelines under SB 743. Building on our MainStreet and TDM+ work, we’re developing a locally-valid spreadsheet tool to calculate project-level VMT impacts and apply VMT reduction measures based on a variety of land use and TDM programs. We’ll revise the City’s existing “CEQA Threshold Guidelines – Transportation Section” to incorporate new screening criteria, general evaluation methods, and thresholds to determine impacts under CEQA when applying the VMT metric. We’ll also support the City as it develops a nexus study to support a VMT-based impact mitigation fee under CEQA guidelines.

Learn more by contacting one of our industry experts.

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