>[!abstract] >The Downs–Thomson paradox (named after Anthony Downs and John Michael Thomson), also known as the Pigou–Knight–Downs paradox (after Arthur Cecil Pigou and Frank Knight), states that the equilibrium speed of car traffic on a road network is determined by the average door-to-door speed of equivalent journeys taken by public transport or the next best alternative. > >Although consistent with economic theory, it is a paradox in that it contradicts the common expectation that improvements in the road network will reduce traffic congestion. In actuality, any improvements in road networks lead to no alleviation of congestion, but usually more use of those roads: what is often referred to as induced demand. Improvements to the road network may even make congestion worse if the improvements make public transport more inconvenient to use, or if they shift investment, causing disinvestment in the public transport system. > >The general conclusion, if the paradox applies, is that expanding a road system as a remedy to congestion is ineffective and often even counterproductive. That is known as Lewis–Mogridge position (Wikipedia, 2024). >[!related] >- **North** (upstream): — >- **West** (similar): [[Braess's paradox]]; [[Jevons paradox]] >- **East** (different): — >- **South** (downstream): [[Marchetti's constant]]