While the level crossing is shut temporarily, people have to use the Cattle Creep.
Most adults have to bow down when they go under this low bridge. The bridge is amazingly low since if the ground level was any lower it would be permanently flooded. In fact it is often a quagmire in the winter even at the current level.
To raise the bridge it would be necessary to move the railway line, which would be horribly expensive. Although children have been known to forget to duck when they cycle through the cattle creep, who cares about the odd brain damaged child? (19/Dec/2009)
This is how a similar problem was solved on the Sustrans route in Lea Marsh.
See also access and Welcome to Walthamstow Marsh & Burnt out vehicle at Cattle Creep.