The Lewis–Mogridge position, named after David Lewis and Martin J. H. Mogridge, was formulated in 1990 and observes that as more roads are built, more traffic consequently fills these roads. Speed gains from some new roads can disappear within months, if not weeks. 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. It is generally referred to as induced demand in the transport literature.