As federal government mulls performance measures, the TTI congestion report returns

By Eric Sudquist

The timing is apparently coincidental, but the Texas Transportation Institute issued its latest estimate of traffic congestion costs in late August, just as US DOT seems to be finishing work on its MAP-21-mandated performance measures on congestion and system performance.

The TTI report measures congestion on highway networks based on the magnitude and duration of slowing compared to free-flow speed, it then calculates time and dollar costs of the additional time spent in traffic. Because it is easy to understand, describes a common experience, and is formatted in a series of lists, it is perfectly suited for uncritical press coverage, which it received.

The report finds that delay, which eased during the recession, is now growing. And while such a finding might be used simply to justify capacity expansions, TTI to its credit points out that there are other ways to reduce delay:

“Businesses can give their employees more flexibility in where, when and how they work, individual workers can adjust their commuting patterns, and we can have better thinking when it comes to long-term land use planning. This problem calls for a classic ‘all-hands-on-deck’ approach,” reports Tim Lomax in an accompanying press release.

The press attention and catholic policy orientation notwithstanding, the TTI approach is widely criticized on both technical and conceptual grounds. For example, in many cases free-flow speeds are above the speed limit, so setting that benchmark is questionable. And the speed of traffic is only a rough indicator of travelers’ ability to access destinations, which is also a function of proximity and mode choice. Other criticisms abound, and many can be found in this post by Rob Puentes at Brookings, and in this and subsequent posts by Joe Cortright at City Observatory.

The conversation is particularly salient now, as the MAP-21 rulemaking on congestion and system performance seems imminent. If FHWA follows the AASHTO recommendation, the rule will be better than the TTI measure, because AASHTO, rather than relying on free-flow speed, would let states and MPOs set the benchmark speed.

FHWA has the opportunity to do even better than that. This report—which came out of a workshop held by SSTI, the Bipartisan Policy Center, and the Eno Foundation—lays out some concepts. What travelers really care about is the time and dollar cost of accessing destinations, and new data and methods offer the ability to track those costs. If the rulemaking simply focuses on vehicle delay, regardless of the benchmark, it will be a missed opportunity to optimize the system for accessibility.

Eric Sundquist is Managing Director of SSTI.