There was a 10K race taking place in London yesterday. Like the London Marathon and other road races, they close the streets to traffic and erect barriers down the side of the road. I was in town for other reasons and I ended up having to cross the route in a couple of places. It can be very tricky, because the flow of runners never stops and there don’t tend to be big gaps between runners. You really don’t want to get in the way of the runners as you cross! In some places you’re not allowed to cross at all, and you have to walk along the route until a gap opens up in the barriers. These kinds of events do pose a problem for pedestrians getting around the city. While traffic gets diverted, there aren’t usually any special provisions made for those on foot.

I had an idea about how to implement a pedestrian crossing to allow people to cross while not affecting the runners. For all I know, this might exist already, but I’ve never seen it used anywhere. Or perhaps it’s totally impractical for some very good reason that marathon organisers know about.

You would need a fairly wide road to do this. In the middle of the road would be an island where pedestrians could stand. In front of the island, facing the runners, would be a sign that told them which side of the island to run on. This could either be an arrow that turns around, or some kind of electronic sign.

As shown in the first picture, initially the arrow points right, directing runners to run on the right of the island. Meanwhile, pedestrians can cross the left hand side of the street to the island.

While runners run to the right of the island, pedestrians can cross the left side of the road.

The island fills up with pedestrians while the runners continue to run past the right-hand side.

The island fills up with pedestrians.

When the island is full the arrow changes to point left. The runners run on the left side of the island. Then the pedestrians can complete their crossing safely.

The runners run to the left of the island, and the pedestrians complete their crossing.

To keep the diagrams simple, I haven’t shown any pedestrians crossing from right to left, but this could obviously happen at the same time. If it was expected to be a very busy area, you could implement separate one-way crossings in different places i.e. one crossing just for pedestrians going left-to-right, and a separate one for right-to-left. To avoid making the runners change direction too much, adjacent crossings could be synchronised so the runners could stick to the same side of the road for both crossings.

I also haven’t shown any sign for the pedestrians to tell them when it’s safe for them to cross, but I think this would be needed for safe operation, just like a standard ‘pelican’ crossing.

At the beginning of the race, when all the runners are bunched up together, you could close the crossing to allow runners to pass both sides of the island. Then when the pack thins out you can enable the crossing.

This type of crossing would enable pedestrians to easily and safely cross the running route during marathons and similar events, without impeding the runners in any way.