While we often hear that road building is not keeping up, the graphs below show that this is not the case. We used TTI data to compare the growth in population and the growth in miles of roadway since 1982, and found that road building is more than keeping pace with the real growth in our metro areas, the growth in population.

Forty-three of the 68 metro areas included in TTI’s study added highway capacity at a greater rate than population growth; four others came very close to keeping pace. The average amount of roadway per person has grown 10% in the last 16 years, meaning that on average we are adding highways faster than we are adding people to drive on them. (see graph, right)

As shown below, eight of the metro areas with the worst rush hour congestion as measured by TTI built enough roads to keep up with the pace of population growth.  Our analysis shows that building highways to keep pace with population may not even be necessary. According to TTI’s data, those metro areas which experienced a decline in the amount of roadway per person actually had slightly lower congestion levels than those metro areas showing an increase of roadway capacity per person.

Some would argue that metro areas should try to keep pace with the growth in driving. According to our analysis of TTI’s data, the amount of driving per person has grown an average of 3% per year in metro areas since 1982. If all the metro areas in TTI’s study were to attempt to build roads at this rate, it would require adding a total of 5,016 lane miles of highway per year at a prohibitive cost. Using a conservative estimate of the cost to add lanes to existing freeways¹, we found that the existing gas tax would have to be raised an average of 17 cents per gallon in the metro areas studied.

Click here to see graphs like the one above for all 68 Metro Areas.  A table containing this information is also available by following this link.

1. Costs were calculated at $1.45 million per lane mile added, which was derived from a study by the Federal Transit Administration (Cambridge Systematics, Inc. et al. Characteristics of Urban Transportation Systems prepared for FTA. USDOT, Publication Number DOT-T-93-07. September 1992.)

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