Skid marks

No, really.

This stretch of road has been, well, a road for as long as I can remember. And then, it was converted to a cycling path. Nice move in itself, because there is an excellent alternative road running in parallel, and it's a nice route by bike.
Apparently this change is not known by all. At least someone had a lot of luck and will never forget it again. Anyone know the "police formula" for calculating speed from length of skid marks?