The reverse may also be true: removing roads may even improve traffic conditions. The Braess Paradox is a famous example in which building new roads in the wrong location can lead to longer travel times for everyone, even without induced demand, because new roads may lead more car drivers to the weakest links in the network. Moreover, it could potentially make congestion across the network even worse. If road capacity expansion does not involve widening of these bottleneck links, congestion may simply move to another part of the network without solving the congestion problem. In Sydney, for example, the WestConnex may improve traffic conditions on Parramatta Road, but may worsen congestion in the city as a whole.Ĭongestion is determined by the weakest links in the road network. To add insult to injury, while more roads may solve congestion locally, more traffic on the road network may result in more congestion elsewhere. In transportation, this well-established response is known in various contexts as the Downs-Thomson Paradox, The Pigou-Knight-Downs Paradox or the Lewis-Mogridge Position: a new road may provide motorists with some level of respite from congestion in the short term, but almost all of the benefit from the road will be lost due to increased demand in the longer term. Very quickly, the drive to work takes just as long as it ever did. If a new road makes driving to work quicker, you may benefit from that.īut this reduced travel time might be enough to encourage two other people in your street to start driving and two more people in the next street and two more people in the street after that and so on.
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