Aug 23, 2008
Published in: Access, no. 35, Fall 2009, p. 16-24
Posted on RAND.org on August 31, 2009
Congestion results from an imbalance between the supply of road capacity and the demand for driving during peak travel hours. RAND was recently asked to evaluate and recommend near term strategies that could meaningfully reduce LA's traffic within a period of five years or less. The authors reviewed general insights from the transportation literature on the causes and potential cures for traffic congestion, and diagnosed the specific local conditions that contribute to the notoriously severe congestion in Los Angeles. Few congestion-reduction strategies remain effective over the longer term. This gradual erosion of congestion improvements comes from a phenomenon called "triple convergence." In short, when traffic conditions on a roadway improve in the peak hours, additional travelers tend to converge on the new capacity from (1) other times of travel, (2) other routes of travel, or (3) other modes of travel, slowly eroding the initial benefits from reduced peak-hour congestion. To further inform the development of suitable strategies to reduce congestion in Los Angeles, the authors took a closer look at some of the underlying factors that contribute to the region's congestion and what implications they have for the types of strategies that might offer the greatest prospects for reducing congestion. Los Angeles' high regional population density is a key contributing factor to congestion issues. Land use patterns in Los Angeles are more polycentric (characterized by multiple centers) than in most other major US cities, making it harder to develop a fast and effective transit system that encourages drivers to leave their cars at home. In addition, the fact that population and jobs are spread out across more centers increases the difficulty of attracting sufficient ridership on any given link to justify the significant investment required for transit lines with dedicated right-of-way. The authors developed an integrated policy framework that could offer the greatest prospects for relieving traffic congestion and improving transportation options in the Los Angeles region. The framework encompasses three key components: --Rely on pricing to manage peak-hour demand, raise needed revenue, and promote more efficient use of existing capacity. --Significantly improve transit and other alternative modes. --Continue to improve the efficiency of the road network, but shift the emphasis from moving cars to moving people. A noteworthy characteristic of these recommendations is that many--particularly those that involve pricing--are certain to stir controversy.