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The Texas Transportation Institute released its latest in a continuous and rigorous series on metropolitan congestion last month.

It is somewhat of a misnomer, as it is not focused on mobility, but congestion.  It is also not focused on mobility as a whole, but traffic.  They can be forgiven, as traffic is more meticulously measured than biking or walking  The only thing better measured is transit, which receives larger public subsidies per passenger trip and involves larger vehicles.  We measure expensive and dangerous things, because the affordable and small things are cheap and safe.  So we wind up managing for the expensive and dangerous things, forgetting that “mobility” just means moving from where we are to where we want to be.  If we can do that on a bike, there is no need to involve a car.

On my first cut of the data (which is quite good and accessible), I looked at the percent of trips in the “urban areas of the study that did not involve traffic.  A study of traffic congestion should be humble to the possibility that people may be getting around by other means.  At the multi-county, census-designated “Urban Areas” level that the TTI study uses, however, the users of other modes are not plentiful.  In the 2010 Census (ACS really), most metros had over 90% of commutes in traffic.

However, the data is revelatory.  Those metros with the highest congestion are also the largest and have the highest transit use.  Its almost like lots of people live and work in rage cities.  It is also almost like transit has always been a response to congestion and busy routes, even unto 1662, 1828, or 1832.

What is even more delicious about the TTI data is that they publish the numbers behind their index.  Particularly % of time congested and % of lane miles congested.  They can measure this now (via Inrix), using the same technology that allows Google maps to tell you about traffic congestion around the city.  All but the most congested cities have the majority of their roads and the majority of there time uncontested.  The percentage of time that our roads are not congested ranges from 85-40%.  The percentage of road miles that are not congested ranges from 48-97%.  It is remarkably easy to avoid congestion in these (largest, most congested) American cities, as long as you don’t need to be on a certain foolish highway at a certain dumb time.  Of course, congested corridors are that way because they connect a lot of people to where they want to go.  Congratulations.


The TTI makes no recommendation with its report, but it doesn’t have to.  The primary datum that traffic engineers use to decide whether a road is good enough is congestion.  If a road gets up to 40% of capacity, it warrants another lane. The ideal is that the same number of cars will have a much easier time traveling down the “improved” arterial.  The reality is that when you decrease the time cost of driving on an arterial, you attract new vehicles to that arterial.  DOTs should not reach out to the “public” living along an arterial slated for “improvement”, they should reach out to those over a mile away who will enjoy calmer roads as a result of the newly crowded arterial to come.  When you live next to a successful arterial, be prepared for repeated seizures of your property and rising traffic noise.  They will never widen your road enough to reduce congestion.

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