Friday, May 20, 2011

More highways and flyovers do not solve traffic problems

The commonest solution to addressing urban transport problems is to expand the road space - either build new roads or widen them or construct fly-overs and elevated express-ways. Planners project it as neat and logical, politicians see it as populist, consultants and contractors view them as cash-cows and people find it sexy. Everyone loves it, atleast in its immediate aftermath.

However, as this post points out, there are serious limitations to this approach. Matthew Philips writes,

"Studies over the last decade (like this one, this one, and this one; plus the book Suburban Nation) have pretty much dismantled the theory that more roads equal less traffic congestion. It turns out that the opposite is often true: building more and wider highways can increase traffic congestion."


Consider the evidence from the US. A 1998 Surface Transportation Policy Project titled "If you Built it, They Will Come: Why We Can’t Build Ourselves Out of Congestion" found that 90 percent of new urban roadways in America are overwhelmed within five years. Another study of 70 urban areas across 15 years concluded,

"Metro areas that invested heavily in road capacity expansion fared no better in easing congestion than metro areas that did not. Trends in congestion show that areas that exhibited greater growth in lane capacity spent roughly $22 billion more on road construction than those that didn’t, yet ended up with slightly higher congestion costs per person, wasted fuel, and travel delay... On average the cost to relieve the congestion reported by TTI [Texas Transportation Institute] just by building roads could be thousands of dollars per family per year."


Another study on the possible impact of the expansion of Washington's highway network finds it unlikely to result in a significant reduction in congestion on the state's roads.


"Academic research and practical experience have demonstrated that increases in highway capacity lead to increases in vehicle travel-reducing, or in some cases negating, the congestion-fighting benefits of the projects."


It suggests increasing investment in transit services and other transportation alternatives, improving the efficiency of existing highways and removing bottlenecks, and ultimately reducing the growth in vehicle-miles traveled (VMT) on the highways. A study by the Texas Transportation Institute finds,

"The effect of lane mile additions on VMT growth is forecast and found to account for about 15% of annual VMT growth with substantial variation between metropolitan areas. This effect appears to be closely correlated with percent growth in lane miles, suggesting that rapidly growing areas can attribute a greater share of their VMT growth to growth in lane miles."


See more evidence from the US on the futility of building (by roads) your way out of congestion in this exhaustive op-ed. This video is an excellent summary of the impact of fly-over demolitions on traffic

Moving Beyond the Automobile: Highway Removal from Streetfilms on Vimeo.



None of this is to argue against road widenings and fly-overs. Given the population sizes involved, municipal governments will be forced to maximize on road carriage-way through widenings and fly-overs. However, as these examples show, we have to be wary of seeing them as part of long-term urban transport problems. A fresh supply of road carriage-way, it appears, creates its own demand!

4 comments:

Aditya said...

The hypothesis that widening of roads and constructing flyovers leads to increased traffic congestion is not completely proven. The hypothesis would have been proven if it was demonstrated with facts that cities which did not expand roads faced less congestion. Moreoever, we need to answer "How" to solve the congestion problem. I would ardently argue for public transportation like Metro rails. It has changed the lives of millions of Delhites and has improved their living standards. Mumbai local is another example but i would advocate for some serious upgradation. Paris is another example where a dense Metro network has allowed 20% of France's population to stay in the city (and suburbs) which was designed in the times of Napoleon and has remained almost same till date. Few people crib about traffic congestion in Paris or we can say few people travel by road in Paris.

Jayan said...

Widening road and (mini)fly-overs are quick fixes. Traffic control should focus on human behavior than vehicle count -- at least in the Indian city of Hyderabad.

gulzar said...

Aditya, thanks for your comment. my caveat at the end is worth repeating,

"None of this is to argue against road widenings and fly-overs. Given the population sizes involved, municipal governments will be forced to maximize on road carriage-way through widenings and fly-overs. However, as these examples show, we have to be wary of seeing them as part of long-term urban transport problems."

the issue here is that, as jayan commented, road widenings and fly-overs are quick-fixes.

at a micro-level, one could easily argue that as roads are widened, economic activity in the road picks up, drawing in more traffic and greater congestion. people, who otherwise would have used an alternative route would now be encouraged to use the widened route more than they otherwise would have. a fly-over, would reduce travel time, and thereby encourage more people to use them. there are several other incetive changes that happens. at some point in time, the pace of change trips over and makes the solution worse than the problem (makes traffic congestion greater than was earlier the case!).

one could just look around in your city and trace out the traffic growth evolution of widened roads.

Anonymous said...

Saying that Vancouver doesn't have traffic problems kind of reduces your credibility. It very much does, although it is largely due to the many bridges which act as choke points.