Urban planners have long debated whether wide, multi-lane roads relieve traffic congestion or, paradoxically, worsen it over time. The phenomenon of…

Urban planners have long debated whether wide, multi-lane roads relieve traffic congestion or, paradoxically, worsen it over time. The phenomenon of induced demand offers an explanation for the paradox: when a road's capacity increases, the lower travel time initially achieved draws in drivers who had previously avoided that route, chosen public transport, or simply travelled less, until congestion returns to roughly its earlier equilibrium level, but now with a far larger total volume of vehicles on the road. Widening a road, on this account, does not solve congestion so much as temporarily relocate it, while permanently increasing the region's dependence on private vehicle travel, a dependence that then makes future attempts to reduce road capacity politically far more difficult than they would have been before the widening occurred.