As cities become more crowded, space utilization and efficiency for transportation become critical to the quality and effectiveness of the transportation network. Improving travel efficiency is also essential for achieving other goals, such as reducing greenhouse gas (GHG) emissions and managing delay or travel time reliability.

Traditional measures of transportation network performance do not provide a complete picture of travel efficiency and have contributed to the land use and transportation decisions in the U.S. that have caused substantial reliance on private automobiles with low levels of vehicle occupancy, better described as seat utilization. This reliance is difficult to change even in California, where state goals for GHG reduction have not translated to lower levels of driving or emissions.

Part of the explanation for today’s outcomes is largely due to the transportation analysis focus on congestion and metrics, such as auto delay and vehicle level of service (LOS). According to these metrics, our problem is that cars are moving too slowly, and physical expansion of the network is necessary to improve network performance. But is this really the case?

While congestion is a problem, slow moving cars are more of a symptom of network performance caused by the ‘root’ problems of poor seat utilization and the mispricing of travel. Solutions aimed at the symptom rarely achieve the goal of eliminating congestion, and in the worst case, exacerbate the long-term problem of congestion due to induced travel effects.