Second Severn Crossing

*Please click the photograph above to access a photo slide show of the Second Severn Bridge

The most southerly bridge over the river Severn is the viaduct and cable-stayed bridge which carries the motorway M4 between Wales and England. It offers an alternative to the earlier suspension bridge, which carries the earlier motorway M4, now called M48. The designers made use of a large area of hard rocks on the western side of the channel, which are exposed at low tide, to enable a viaduct to be built. The main channel, called The Shoots, is spanned by the actual cable-stayed bridge.

The bridge is not far from the line of the Severn tunnel, which was a great feat of engineering, built from 1874 to 1886. Huge pumps were, and are, needed to remove water, and very large fans were installed to provide ventilation.

This new Severn bridge is quite close to the ferry crossing that was used by the Romans in the days of the empire, illustrating, as many Severn bridges do, that the number of good crossing points is limited, and that people will use them during long periods of time.

The bridge has high baffles on each side to deflect the wind. This greatly reduces the number of occasions on which any type of vehicle has to be banned from the bridge because of high winds. The transition from normal road to bridge is in fact so well done that it is easy to get well on to the bridge without realising it.

The large tidal range exerted a big influence on the construction work. Timing was crucial in operations such as floating out and raising sections of the bridge. Positioning of floating equipment was achieved using signals from navigational satellites. The picture at left was taken at a late stage in construction. On this occasion the tide was low, revealing the the English Stones, a large area of rocks on the eastern side of the channel. The cable-stayed bridge was complete, and the last few approach spans remained to be added.

The approach spans are based on post-stressed hollow beams, made from 3.5-metre match-cast sections which were floated out on a barge at high tide.

Here are some facts and figures about the new bridge. The total length is just over 5000 metres, with a main span of 456 metres in a main bridge of 947 metres length. The number of approach spans is 45, divided between the Welsh end, 22, and the English end, 23. The bridge was built from 1992 to 1996. Click here for more about cable-stayed bridges.

Link: Severn River Crossing