Automatic street widening: Evidence from a highway dedication law

Abstract

Cities often require developers to widen streets or make other transportation improvements to account for the traffic impacts of new building. This article examines one parcel-level traffic mitigation law in depth—the highway dedication ordinance of the city of Los Angeles. I first show that the law emerged from a combination of happenstance and political and fiscal constraints, not from persuasive evidence it would be effective. I then show that the traffic predictions underlying the law are often inaccurate, and that, in fact, the standards the law is based on are in some ways unverifiable. Thus the law likely does little to reduce congestion and probably impedes housing development. Finally, I argue that the law persists precisely because its desired outcome is hard to verify: Without measurable goals, planners fall back on a measurable process. Parcel-level traffic mitigation becomes an exercise not in reducing traffic but in ensuring that developers carry out mitigations, regardless of whether those mitigations are effective.