The Blackwall Tunnel in London has a something similar with heavy metal weights on chains. http://www.sabre-roads.org.uk/forum/viewtopic.php?f=1&t=6447 http://w

The Blackwall Tunnel in London has a something similar with heavy metal weights on chains. http://www.sabre-roads.org.uk/forum/viewtopic.php?f=1&t=6447 http://www.sabre-roads.org.uk/forum/viewtopic.php?f=1&t=... These will make a fair mess of a vehicle, I saw them hitting a lorry once but are pretty attention grabbing. The Blackwall Tunnel has different heights and widths for different lanes due to the tunnel profile which is why the restrictions are different in each lane in this photo.