After a request to cross (by button press), a kerb side detector monitors the pedestrian's presence at the crossing. Should the pedestrian cross prematurely, walk away from the crossing, or wait outside the detection area, the pedestrian's request to cross could be automatically cancelled. This is so traffic is not halted unnecessarily. An on-crossing detector ensures that the signal for vehicles remains red until pedestrians have finished crossing (within practical limits). Unlike the pelican crossing, there is no transitional "flashing" phase.