why does adding more traffic lanes doesn’t help to alleviate traffic congestion?
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I have a city planning degree. Adding more lanes will always reduce congestion in the short term. In the long term it will never reduce congestion. But “long term” is defined very differently depending on the area.
Others have used the term induced demand, and it’s the correct answer, but it helps to understand exactly what that means. If roads are congested, some people will stay home rather than drive, or, more particularly … they will live somewhere else.
Now widen the road into a beautiful new wide thoroughfare. People suddenly are fine with driving since the congestion is lower ***and*** developers are suddenly eyeing the area a lot more closely looking to build housing and market the “ease” of driving on the new highway. So they build more, and more people move in, and the people who didn’t drive suddenly start driving … and hello, the road is right back where it was, after $500 million of taxpayer money was spent.
This process can take a very short time or a long time. In hot cities, like Atlanta or Houston, highway widening projects are doomed to fail almost immediately — within two years, they are probably going to be the same level of congestion or worse. Expansion projects in slightly less “desirable” or hot markets will take longer to reach this stage. Either way, the long term investment does not pay off.
It is important to note that this will happen with construction of commuter rail as well, which is something people bring up a lot. If you build commuter rail instead of widening the road, then yes, congestion will ease a little bit, until, whoops, more cars suddenly show up to fill the space vacated by the new train riders.
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