Parallel to the A13 near Overschie a road tunnels underneath the Doenkade (N209). Signs on both sides are warning that the passage is only 400 cm high. Perhaps the tunnel shrunk over the years due to the peaty soil and a fluctuating groudwater level. Or perhaps gaining time and avoiding the A13 traffic jams is worth losing the 400+ paint, I don’t know.
What happened is that the tunnel-ceiling looks like an abstract expressionist canvas.