New Study Reexamines Causes and Costs of Congestion

This new study by CEOs for Cities critiques methods used to measure traffic congestion costs and evaluate congestion reduction strategies. It criticizes the Travel Time Index (TTI) used in the commonly-cited Urban Mobility Report as an unreliable guide for understanding the nature and extent of urban transportation problems. The TTI uses flawed speed and fuel economy estimates which overstate traffic congestion costs, and it ignores the increased transportation costs associated with more dispersed land use patterns. As a result, the TTI favors policies that stimulate automobile dependency and sprawl.

The Urban Mobility Report's claims about growing congestion do not correlate with other measures of travel times. Urban Mobility Report's estimates of congestion delay are inconsistent with real-time traffic data, and travel times reported in travel surveys.

Driven Apart recommends that urban transportation system performance be evaluated based on Hours of Peak Period Travel, which recognizes the time and fuel cost savings that result from more compact and mixed land use which reduces travel distances. It recommends a new approach to measuring urban transport system performance that reflects these elements:

1. Emphasize accessibility - the proximity and convenience of destinations - not just mobility.

2. Include comprehensive measures of land uses, trip lengths and mode choices as well as travel speeds.

3. Incorporate new and better data on travel speeds and commuting patterns.

4. Adopt an open, multi-disciplinary process to select, validate and continuously improve measures.

5. Provide measures that can be used to guide policy and evaluate investments rather than simply raise alarm about traffic delays.