March 14th - This is for Richard Burnell. Last autumn, he was exploring the canals of Birmingham, and he happened upon these boxes, mounted either side of the canal in Ladywood. He asked what they were, and I told him - to some incredulity - that they were a traffic counter. I vowed that next time I passed, I’d take a picture or two.
In the tall metal box is a mains power supply and a counter. In the long, flat one next to it, two photo electric beam switches (made by specialists Sick), which detect a light beam reflected from a target in the box on the opposite side of the canal. When both beams are broken together, it’s most likely by a boat, so the count increases. By using the two beams, this filters out false signals from curious hands, waterfowl etc.
Measuring boat traffic is important. Similar systems on cycle routes count bikes, and we’ve all seen the temporary ones that count traffic.