This article, written by Todd Litman and published on Planetizen, broaches the possibility that the Texas Transportation Institute’s methodology for their annual Urban Mobility Report is flawed by using unrealistic expectations as a benchmark for measuring the cost of congestion. He suggests that a more realistic measurement of cost could be derived by using a congestion benchmark other than a grade “A” level of service (free-flowing traffic), instead using a benchmark of grades “D” or “C” (equivalent to a moderate level of congestion). This is similar to how Metro determines whether a particular roadway is adequate for its modeling of Region 2040 traffic levels, because they do not define the goal for all roadways as “free-flowing traffic,” instead choosing to acknowledge that a certain level of congestion is to be expected in a region with a healthy economy.
Additionally, Todd covers how other issues factor into the measurement of overall cost including providing parking, vehicular accidents, pollution, roadway maintenance, and even the cost of vehicle ownership.
The newest Texas Transportation Institute Urban Mobility Report was recently released, stimulating discussion of congestion costs and potential solutions. Here are some things you should know when evaluating these issues.
There are many several possible ways to measure congestion costs. The method used by the Texas Transportation Institute leads to relatively high cost values, since it assumes that “optimal” roadway conditions are freeflow (level-of-service A), although many transportation economists consider this assumption is inappropriate (see for example, the 2006 report, Costs of Non-Recurrent Congestion in Canada). They argue that congestion costs should be calculated above an optimal threshold, such as level-of-service C or D, which leads to significantly lower cost estimates.