An analysis by the Texas Transportation Institute shows

An analysis by the Texas Transportation Institute shows that road widening has had virtually no impact on the growth of traffic congestion in major urban areas in the last 15 years. The analysis by the Surface Transportation Policy Project (STPP), a coalition of over 200 environmental and consumer groups, compiled averages of TTI’s “Roadway Congestion Index” for two categories: metropolitan areas that have added new road capacity in the past 15 years and those that have not. While the averages of the two groups are almost identical, at 0.93 and 0.92 respectively, the areas adding more new lanes spent roughly $22 billion more on construction. The STPP report says the problem may be partially explained by the phenomenon of “induced traffic.” Several recent studies have documented that new roads actually encourage more driving rather than easing the effects of congestion.