crocat

We can test this by putting two chimneys close together and seeing if we get a diffraction pattern of presents and coal.

In the UK pedestrians will never have a green light while cars have a green light and the timings wait until pedestrians will have finished crossing before allowing cars. There might be some slow walkers or people who crossed without green (it's dangerous but not illegal) but everything is done to ensure neither pedestrians nor cars are told to go while the other isn't told to stop.