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
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!