Today we review an analysis by Todd Litman of the Urban Mobility Report in which he criticizes the relatively narrow engineering view taken of congestion which tends to exaggerate the costs of traffic and leads to more road building aimed at increased vehicle speeds without considering other options which would benefit mobility in general, safety and the environment at lower cost. When compared with other vehicle costs, congestion comes out a lower one compared to car ownership, operations and parking- something that road builders seldom consider.
Key Quotes:
“The Urban Mobility Report’s analysis is biased in ways that overestimate congestion costs and roadway expansion benefits. To the degree that this occurs, decision-makers will overinvest in roadway capacity expansion and under-invest in alternative solutions that are more cost effective and beneficial overall…the traffic engineering perspective assumed in the UMR reflects a narrow perspective that is unsuitable for addressing complex urban transportation problems.”
Differing views of congestion:
- “Economists consider congestion a symptom of underpricing (prices below marginal costs), and evaluate solutions based on overall cost efficiency and users’ willingness-to-pay for faster travel”
- “Progressive transport planners evaluate transport system based on accessibility rather than just mobility, and consider vehicle travel speeds just one factor that affects overall accessibility”
- “Urban economists recognize that traffic congestion tends to maintain equilibrium: it increases to the point that it discourages additional peak-period vehicle trips, causing some travelers to choose alternate times, routes, modes and destinations….. a certain amount of congestion is unavoidable and not a problem provided that people and businesses have suitable alternatives”
“the increased proximity provided by more compact development has about ten times more influence on accessibility (the number of jobs and services available within a given time period) than a proportional increase in vehicle traffic speed”
“adding traffic lanes and reducing cross streets on urban arterials can increase traffic speeds, which improves automobile access, but creates barriers to walking and cycling (called the barrier effect),reduces roadway connectivity, and stimulates more dispersed development patterns which increase the distances that must be traveled to reach destinations”
“Higher travel speeds require more shy distance between vehicles which reduces roadway capacity. For example, at 60 mph a highway lane can accommodate up to 700 vehicles per hour, about half of what it can carry at 45-55 mph”
“Because congestion is just one of many costs, it is inappropriate to evaluate congestion reduction strategies in isolation”
“These omissions and biases all skew toward overestimating congestion costs and roadway expansion benefits.”
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