Class 3 invalid carriage - Powered wheelchairs and other outdoor powered vehicles, including scooters
Means a mechanically propelled invalid carriage which is so constructed or adapted as to be capable of exceeding a speed of 4 mph (6 km/h) but incapable of exceeding a speed of 8 mph on the level under its own power.
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If you are riding a Class 3 vehicle, you must ensure that you switch to the 4mph (6 km/h) on pavements or in pedestrian areas.
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Another scenario on a junction I use regularly
traffic light T junctions, 2 way, with pelican crossing immediately turning off main road, that is optionally also part of light sequence - ignoring common sense,
can pedestrians ignore the red man, and cross in front of cars turning off main road.