Why exactly do cities build new housing?

The most probable answer to this question is that it is expected that more people are to move in as a result of new opportunities. And in the times before the onset of the COVID-19 pandemic, it was expected that people would have to travel from their homes to work. Therefore, an increase in the housing supply held the potential to change the traffic dynamics of a particular area, whether it be a new car on the road or more people in the streets. To ensure that this new change is manageable, Transportation Impact Assessments (more informally known as Traffic Studies) have to be completed for any new development in Los Angeles.     

To put it simply, traffic studies are quantitative and qualitative analysis that determine the impact of new housing development has on the surrounding transportation system. Although traffic studies used to be concerned with primarily cars, they have evolved to include a much more holistic vision, such as the safety of pedestrians. Traffic studies are mandated for most developments under the California Environmental Quality Act (CEQA) so the public has an understanding of what the new development might bring and decide how to move forward with the project. If it turns out that the new development might bring too much traffic, then modifications can be made to mitigate the impacts.

Traffic Study Metrics

From the mid-century until 2018, all traffic studies in the state of California primarily

measured the effects of a project on generating traffic in an intersection (also known as Level of Service or LOS). If a project’s impact was too large, then a typical mitigation was to generate more road capacity (such as bigger intersections). If the development was in a dense area where the streets were already at their maximum width, then it would be virtually impossible to build something that would provide a large amount of housing units without creating unavoidable significant impacts. This was a vital part of the state’s CEQA code, which meant that the environmental-friendliness of new housing developments would be measured by how much more difficult they made traffic. Resultantly, suburban sprawl was promoted by state code while dense-infill developments were penalized.

         In 2013, The state government decided that this needed to change with the passage of Senator Darrell Steinberg’s landmark bill SB 743. SB 743 recognized that the old automobile-centric system of level of service was harmful to communities and the planet, and that a paradigm shift was necessary to commit California to climate and social justice. Adopted in its place would be Vehicle Miles Travelled, also known as VMT. As the name implies, Vehicle Miles Travelled measures how many vehicle miles that will be generated by a development. To illustrate, although a single-family house built in the exurban fringes of the San Fernando Valley will not add much more housing capacity, the people who live there will have to travel long distances to get to where they need to be, generating a large number of vehicle miles travelled. Conversely, a dense multi-family development in Koreatown will bring a lot of new residents, but not many VMTs since people can walk and take transit to work and activities. VMTs will often be divided by the total population of the new development to obtain how many VMTs are created per-capita. This way dense urban infill development will be incentivized while suburban sprawl will be penalized.

         Although SB 743 was signed into law in 2013, it took many years for the state to develop the new VMT metrics, and ultimately the state gave cities until July 1, 2020 to adopt VMTs as the new metric. Los Angeles adopted the changeover in 2019, an entire year ahead of schedule!

The Traffic Study Process

So now that we know how traffic studies are measured, how exactly can we initiate and complete one?

The entire journey will start out with an experienced professional. Consultants (and sometimes city staff) will be contacted by a developer with a request for a traffic study for a particular project. In the City of Los Angeles, traffic studies are typically required unless the project generates less than 250 daily trips or is 100% affordable housing. The professional will then meet with the local jurisdiction (for a project happening in the City of Los Angeles this will be LADOT) and discuss what the possible issues might be and what the scope would look like. After coming to an agreement with them, the consultant or city staff will then proceed with the study.

In the City of Los Angeles, this will begin with a very particular tool called a VMT calculator. The City of Los Angeles has prepared an excel spreadsheet tool which allows for an individual to enter in the project’s address, existing and proposed land-use type (such as single-family, multi-family, or mixed-use) at the location, and number of unit and return the number of daily vehicle trips and VMT expected for the existing and proposed development. The tool is quite sophisticated, and allows for the user to choose from a variety of land-use types, ranging from multi-family housing to affordable housing to schools! If you’re curious to try the tool out, just check out the application right here.

In addition to the VMT calculation, Non-CEQA components will have to be analyzed. These include driveway access, intersections up and down the block, commercial projects near residential neighborhoods and cut through traffic, and a review of pedestrian and transit and review part of access around (like is a sidewalk missing?). Afterwards, the professionals preparing the traffic study will have it reviewed by city staff. After back and forth discussion and edits, it will be incorporated into the environmental document for the project (such as an environmental impact report or EIR), which is in turn sent out for public review and comments through CEQA.

In the public review session, local residents and concerned individuals will be able to show up and speak their minds about the impacts on travel that the new project may bring. For some NIMBYs, this may represent the perfect time to delay or downsize the project by saying the traffic impacts will be too heavy or that the study must include more aspects. Some professionals are preemptive of this and commit to a “leave no stone unturned” policy of taking into account every possible avenue in the traffic study. In other words, instead of just performing the study on the “low-hanging fruit” impacts, every single possible perturbation of impacts may be looked at. Once this process is completed, the project can go forward. A single traffic study can cost around $30,000 to $50,000 on average, and much higher for more complex projects.


Understanding how a new development affects the flow of travel in an area is vital for any new development. Whether it be through level of service or vehicle miles traveled, the community needs a way to grasp potential impacts before committing to a decision. Any developer needs to be aware of their importance, as failure to do so can be the undermining of even the most well-designed project. To lead Los Angeles towards a more housing abundant future, local policy makers should push forward legislation on making traffic studies even more complementary towards more production. Potential actions range from taking VMTs out of CEQA and therefore reducing its potential to stop projects to removing VMT limits for developments in dense urban areas so hyper large projects can be created.



This article would not have been possible if it was not for a Qazi Aniqua Zahra, Saima Musharrat, and Tom Gaul.

Qazi Aniqua Zahra is a Planning Analyst at Port Authority of Allegheny County in Pittsburgh, PA. Qazi completed her Masters in urban planning at Texas A&M University and is an environment enthusiast with an interest in planning for resilient communities. Qazi was able to connect the author with…

Saima Musharrat is a transportation planner for Fehr & Peers who has an in-depth understanding of urban systems, land use policy, physical land planning, multimodal transportation, community development and energy efficient design principles in architectural and urban development. Saima was able to connect the author with…

Tom Gaul. Tom is a Principal at Fehr & Peers and has nearly four decades worth of experience in traffic studies and uses his degree in civil engineering to push the frontier of urban planning. Tom, thank you for taking the time out of your busy schedule to inform me how the traffic study process works.