Why isn't there a road bridge over the English Channel which connects Britain to mainland Europe?

Answer 1

Because they built a tunnel instead.

The English Channel is unusual because of the large amount of shipping which goes through and across it, and the fact that does not have just one shipping lane, the shipping traffic covers the complete width of the Channel.

The longest single bridge span in the world is about 2 Km (when the Channel Tunnel was being planned in the 1980's it was the Humber bridge at 1410 metres). The Straits of Dover, the narrowest part of the Channel, is 34 Km wide, A bridge would need about 20 bridge supports standing in the water. Sooner or later a ship would accidentally crash into one of them and bring the bridge down. No bridge support can be strong enough to withstand a crash with a fully laden cargo ship.

Other long bridges have the luxury of a narrow channel through which all the ships travel. These bridges cross the shipping channel in one span, they have shorter spans for the shallower water each side.

The only alternative was a tunnel. Road tunnels need ventilation shafts every 1 - 2 Km, because the engines consume large amounts of oxygen and put out poisonous fumes. You equally cannot have air shafts in mid-channel, a ship would hit them and flood the tunnel.

So the option they chose was a railway tunnel using electric trains, which allowed direct high speed trains London - Paris etc., and cars and freight vehicles being carried on shuttle trains through the tunnel.