Lewis-Mogridge Position
Updated 2026-08-03
INTRODUCTION
English translation pending.
CORE DEFINITION
The Lewis-Mogridge position, drawn from studies of London traffic in the 1960s and 1970s, states that traffic grows to fill the road space available for it. Adding lanes shortens travel times, which lowers the cost of driving and therefore induces new trips, so congestion returns to its former level or worse. The underlying mechanism is induced demand, and the position echoes the Downs-Thomson paradox. Its general lesson is that in a constrained system, raising supply alone reignites latent demand, so expansion must be paired with demand management.
SCAFFOLDING EFFECT
Reduce cognitive load
- Supply suspicion: When more capacity is promised to end a shortage, ask what latent demand it will wake. - Demand pairing: Attach every supply increase to a demand control, such as pricing or priority rules. - Per-person accounting: Judge improvement by service per user rather than by the total capacity added.
Anchor fast decisions
Road space is not consumed but occupied by choice, so its cost shapes how much of it is used. Adding capacity makes each trip cheaper in time, and cheaper trips call forth drivers who had stayed home, switched modes, or traveled at other hours. The new trips absorb the new lanes and travel times creep back to the old equilibrium, which is why pure supply expansion rarely pays for itself in relief.
MINIMUM ACTION
In progress 0/1Practice this model in one real situation:
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Source support: Explicit
- en.wikipedia.orghttps://en.wikipedia.org/wiki/Lewis%E2%80%93Mogridge_positionverified
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