Lewis-Mogridge Position
Encyclopedia
The Lewis–Mogridge Position, named after D. Lewis and M. J. H. Mogridge, was formulated in 1990. It captures the observation that the more roads are built, the more traffic there is to fill these roads. Speed gains from some new roads can disappear within months if not weeks. Sometimes new roads do help to reduce traffic jams, but in most cases the congestion is only shifted to another junction.
The position reads traffic expands to meet the available road space (Mogridge, 1990). It is generally referred to as induced demand
in the transport literature, and was posited as the "Iron Law of Congestion" by Anthony Downs
.
Following the Lewis-Mogridge Position it is not generally concluded that new road
s are never justified, but that their development needs to consider the whole traffic
system. This means understanding the movement of goods and people in detail, as well as the motivation behind the movement.
The Lewis-Mogridge Position is often used to understand problems caused by private transport
, such as congested roads in cities and on motorways. It can also be used to explain the success of schemes such as the London congestion charge
.
The position, however, is not confined to private transport. Mogridge, a British transport researcher, concluded also that all road investment in a congested urban area will have the effect of reducing the average speed of the transport system as a whole — road and public transport
. This relationship and overall equilibria is also known as the "Downs-Thomson paradox
". However, according to Anthony Downs
this link between average speeds on public transport and private transport "only applies to regions in which the vast majority of peak-hour commuting is done on rapid transit systems with separate rights of way. Central London is an example, since in 2001 around 85 percent of all morning peak-period commuters into that area used public transit (including 77 percent on separate rights of way) and only 11 percent used private cars. When peak-hour travel equilibrium has been reached between the subway system and the major commuting roads, then the travel time required for any given trip is roughly equal on both modes."
The position reads traffic expands to meet the available road space (Mogridge, 1990). It is generally referred to as induced demand
Induced demand
Induced demand, or latent demand, is the phenomenon that after supply increases, more of a good is consumed. This is entirely consistent with the economic theory of supply and demand; however, this idea has become important in the debate over the expansion of transportation systems, and is often...
in the transport literature, and was posited as the "Iron Law of Congestion" by Anthony Downs
Anthony Downs
Anthony Downs is a scholar in public policy and public administration, and since 1977 is a Senior Fellow at the Brookings Institution in Washington D.C..-Education:...
.
Following the Lewis-Mogridge Position it is not generally concluded that new road
Road
A road is a thoroughfare, route, or way on land between two places, which typically has been paved or otherwise improved to allow travel by some conveyance, including a horse, cart, or motor vehicle. Roads consist of one, or sometimes two, roadways each with one or more lanes and also any...
s are never justified, but that their development needs to consider the whole traffic
Traffic
Traffic on roads may consist of pedestrians, ridden or herded animals, vehicles, streetcars and other conveyances, either singly or together, while using the public way for purposes of travel...
system. This means understanding the movement of goods and people in detail, as well as the motivation behind the movement.
The Lewis-Mogridge Position is often used to understand problems caused by private transport
Private transport
Private transport, as opposed to public transport, is transportation service which is not available for use by the general public. Private transport is the dominant form of transportation in most of the world. In the United States, for example, 86.2% of passenger miles traveled occur by passenger...
, such as congested roads in cities and on motorways. It can also be used to explain the success of schemes such as the London congestion charge
London congestion charge
The London congestion charge is a fee charged for some categories of motor vehicle to travel at certain times within the Congestion Charge Zone , a traffic area in London. The charge aims to reduce congestion, and raise investment funds for London's transport system...
.
The position, however, is not confined to private transport. Mogridge, a British transport researcher, concluded also that all road investment in a congested urban area will have the effect of reducing the average speed of the transport system as a whole — road and public transport
Public transport
Public transport is a shared passenger transportation service which is available for use by the general public, as distinct from modes such as taxicab, car pooling or hired buses which are not shared by strangers without private arrangement.Public transport modes include buses, trolleybuses, trams...
. This relationship and overall equilibria is also known as the "Downs-Thomson paradox
Downs-Thomson paradox
Downs-Thomson paradox , also referred to as the Pigou–Knight–Downs paradox , states that the equilibrium speed of car traffic on the road network is determined by the average door-to-door speed of equivalent journeys by public transport.It follows that increasing...
". However, according to Anthony Downs
Anthony Downs
Anthony Downs is a scholar in public policy and public administration, and since 1977 is a Senior Fellow at the Brookings Institution in Washington D.C..-Education:...
this link between average speeds on public transport and private transport "only applies to regions in which the vast majority of peak-hour commuting is done on rapid transit systems with separate rights of way. Central London is an example, since in 2001 around 85 percent of all morning peak-period commuters into that area used public transit (including 77 percent on separate rights of way) and only 11 percent used private cars. When peak-hour travel equilibrium has been reached between the subway system and the major commuting roads, then the travel time required for any given trip is roughly equal on both modes."