london box
Inner London motorway system planned in the 1970s but never built (hence the horrendous jams today). Term can be used for any worthwhile government project that never materialises, such as the often touted "Birmingham underground" system.
The government will never build an underground system in Birmingham. It will be just like the London Box. Maybe there was a deal in the 1960s that Birmingham will get reasonable roads and London will get reasonable trains.