Lewis–Mogridge position

Sometimes, new roads 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.

[1] It is a special case of Jevons paradox (where the resource in question is traffic capacity), and relates to Marchetti's constant (average commute times are similar in widely varying conditions).

The position is often used to understand problems caused by private transport such as congested roads in cities and on motorways.