Traffic Analysis in Project Review: From LOS to VMT

Traffic is the most common objection raised against a proposed project and the least commonly understood part of the review that follows. A resident says the streets cannot take it. A consultant produces a study. The study says something that does not appear to answer the objection, and everyone leaves the hearing frustrated.

Most of that frustration comes from a genuine mismatch. The question residents ask and the question the analysis is required to answer are not the same question, and California changed which question governs.

This describes how the analysis works. Anthony is a Realtor, not a traffic engineer or a land use attorney, and nothing here is a prediction about any particular street.

What a traffic study is for

A traffic study is not neutral background research. It exists to serve a decision, and which decision it serves determines what it measures.

Studies generally appear in two places. One is environmental review, where the question is whether a project causes a significant impact on the environment under state law. The other is project conditioning, where the question is what the city may lawfully require the applicant to build or pay for. The environmental side is covered in the guide to CEQA and project timelines, and the conditioning side in the guide to conditions of approval.

Keep those two apart. A finding of no significant environmental impact does not mean nothing about traffic can be required of a project; a required improvement does not mean an impact was found.

Level of service, and what it measured

For decades the standard measure was LEVEL OF SERVICE, usually written LOS. It is a letter grade describing delay at an intersection or on a segment, from free flow at the top to sustained congestion at the bottom.

LOS is intuitive. It maps directly onto the experience of sitting at a light, which is exactly what residents complain about, and it produces a clean threshold: if a project pushes an intersection below an adopted standard, the project has a problem to solve.

It also had a structural consequence that took years to become obvious. Because LOS measures delay to vehicles, the remedy for a bad LOS score is almost always more vehicle capacity: a wider intersection, an added lane, a longer turn pocket. Applied consistently over decades, that logic widens roads and makes driving the easiest way to move, which generates more driving.

A second consequence mattered for infill towns specifically. A project in an already-developed, well-connected place tends to score worse on LOS than the same project on an open site at the edge of a region, because the developed place already has traffic. The measure penalized building in the places that generate the least new travel per household.

The shift to vehicle miles traveled

California responded by changing the metric used for transportation impacts in environmental review. The governing measure became VEHICLE MILES TRAVELED, or VMT: how much driving a project causes, not how much delay it adds at a nearby corner.

The reasoning follows from what environmental review is for. Delay is a matter of local convenience; total driving connects to emissions, energy use, and regional air quality, which are the effects the statute concerns itself with.

The practical effects are worth stating carefully.

An infill project near jobs, services, and transit tends to perform well on VMT, because the households it adds are expected to drive less per capita than the regional average, even though it may add cars to a specific intersection.

A project at the periphery, generating longer trips, tends to perform poorly on VMT, even where the adjacent road is empty.

Mitigation looks completely different. Widening a road does not reduce VMT and may increase it. Measures that shorten or replace trips do: proximity to services, transit access, parking strategy, bicycle and pedestrian connections, unbundled parking, mixed uses.

Why residents feel unheard

This is the mismatch at the center of most traffic disputes.

A neighbor's objection is a delay objection. It is about the left turn, the school pickup, the queue at the corner. Under the current framework, that objection is not the environmental question, and a study may conclude that the transportation impact is less than significant while the neighbor's experience of the intersection gets worse.

Saying so plainly is more honest than pretending otherwise. It also points at where the concern can still land.

Local operations are not outside the city's reach; they are outside the environmental finding. Cities routinely evaluate circulation, safety, sight distance, queuing, and access as part of project design and conditioning, through the general plan's circulation policies, through design review of the kind described in the guide to design review, and through improvements in the public right of way of the kind covered in the guide to encroachment permits.

The way to be heard, then, is to raise operations as an operations issue rather than as an environmental one, and to be specific: a movement, a time of day, a sight line, a conflict point.

How to read a traffic study

Five things determine what a study can honestly claim.

THE STUDY AREA. Which intersections and segments were included, and why those.

THE BASELINE. What conditions the analysis compares against, and when counts were taken. Counts collected during an unusual period deserve a question.

THE TRIP GENERATION AND REDUCTIONS. How many trips the land use is assumed to generate, and what reductions were credited for transit, walking, or internal capture.

THE CUMULATIVE SCENARIO. Whether other reasonably foreseeable projects were included, since the honest version of the neighbor's complaint is usually cumulative rather than about one building.

THE MITIGATION LOGIC. What is proposed, who builds it, and when. Timing is frequently the weak point: an improvement promised at a later phase is worth less than one delivered at occupancy.

All of this sits in the technical appendices of the project record, which the public may inspect. The retrieval process is in the guide to requesting planning records.

The limits

Transportation analysis methodology is set by state guidance and local implementation, and both are revised. Thresholds, screening criteria, and accepted mitigation approaches differ between agencies and change over time.

For how any specific proposal was analyzed, what standards were applied, and what the city required, go to the City of Claremont, which holds the study and the staff evaluation of it.

For the wider picture, start at the City Development hub and the overview of how Claremont grows. Anthony Grynchal has been licensed in California since November 2009.