Motorcycles and scooters have much less mass than cars, resulting in a failure to trigger the sensor, while bicycles may not even be constructed with metal.

A system that sprays sterilising alcohol mist around the cabin pumped out too much - triggering a sensor designed to stop drink-driving and shutting it down for six hours!

Operators at video response centres are alerted if an attempted breach triggers the sensors.

Players must trigger the sensors by moving their arms (or other body parts) under the sensors when a corresponding arrow reaches.