One of Melbourne's most important road bridges is in urgent need of work so both trucks and cyclists can continue to use it safely, an expert report given to the Napthine government has found.

The VicRoads report says the ageing Shepherd Bridge, in Footscray, has cracked pedestals and corroded steel bearings and needs strengthening and repair to cope with growing truck traffic.

Used by 40,000 vehicles a day - up to 20 per cent of them trucks - the bridge, one of just two cycling routes between the inner west and CBD, is crossed by more than 2000 cyclists a day. Making it safer for cyclists is VicRoads' top cycling project for Melbourne's west, the report said. It proposed strengthening the bridge and widening and separating the narrow bike path, now shared with pedestrians, at a cost of $13.5 million.

''There is a significant strategic opportunity to improve the bicycle priority at this key location approaching Footscray, in order to more efficiently bring people into the centre of Footscray and the CBD and reduce the impact of traffic congestion on the road,'' said the report, which was released to the Victorian Greens under freedom-of-information laws.