Downs-Thomson Paradox

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The Downs-Thomson Paradox (named after Anthony Downs and John Michael Thomson) states that the average speed of car traffic on a road network is determined by the average door-to-door speed of equivalent journeys on public transport.

It is paradoxical that improvements in the road network will not reduce traffic congestion. Improvements in the road network can worsen congestion if the improvements make public transport more inconvenient or if they shift investment, resulting in lower investment in the public transport system.

Instead of public transport, the bicycle can also be seen as a “replacement”, as is the case, for example, in many Dutch cities.

consequences

The general conclusion, if the paradox is true, is that upgrading a road system as a remedy for congestion is ineffective and often counterproductive.

A 1968 article by Dietrich Braess pointed to the existence of counterintuitive occurrence in networks: Braess' paradox is that adding additional capacity to a network when the moving units selfishly choose their route, in some cases, the overall performance of the Traffic system can decrease.

There is interest in studying this phenomenon as it can happen in both computer networks and transport networks. The expansion of the network is characterized by the behavior of users similar to that of travelers in transport networks, who act independently and in a decentralized manner when choosing optimal routes between starting and destination. This is an extension of the induced demand theory and is in line with Downs' "triple convergence" theory of 1992, which was formulated to explain the difficulty of clearing highways congestion at peak times. In response to an increase in capacity, there are three immediate effects:

  • Drivers using alternative routes are starting to use the extended freeway
  • those who previously drove at low-traffic times (either immediately before or after the peak of traffic) shift to the peak of traffic (rescheduling behavior as previously defined)
  • public transport users are shifting to driving.

"The average speed at which private vehicle (passenger) users reach their destinations is directly related to the speed at which public transport users reach their destinations."

Limitation of validity

According to Downs, the link between the average speed of public passenger transport and private transport is only dependent “in regions where the majority of commuting during rush hour is via rapid transit systems with separate rights of way. Central London is an example of this, as in 2001 around 85 percent of all morning rush hour commuters in this area used local public transport (77 percent of them with separate right of way) and only 11 percent used their private car. If the equilibrium between the subway system and the main thoroughfares is achieved at rush hour, then the time required for a journey is approximately the same on both modes of transport. "

See also

  • Braess paradox , additional options for action (for example more roads) can lead to a poorer overall result in the case of individual-rational decisions
  • Jevons paradox , an increase in efficiency tends to increase (and not decrease) the rate of consumption of this resource

swell

  • Dietrich Braess: About a paradox from traffic planning. 1968, translated from German as On a Paradox of Traffic Planning by Dietrich Braess, Anna Nagurney, and Tina Wakolbinger (2005) In: Transportation Science 39/4, 446-450.
  • Anthony Downs: Stuck in Traffic: Coping with Peak-Hour Traffic Congestion. The Brookings Institution, Washington 1992 (DC)
  • Martin JH Mogridge: Travel in towns: jam yesterday, jam today and jam tomorrow? Macmillan Press, London 1990.
  • John Michael Thomson: Methods of traffic limitation in urban areas. Working Paper 3, OECD, Paris 1972.

Individual evidence

  1. ↑ The Downs – Thomson Paradox with responsive transit service . June 15, 2020.
  2. ^ Public report Rijkswegennet (Dutch) . June 15, 2020.