No-one goes on a runway without positive ATC clearance, even emergency vehicles.

In Germany at least, if the runway access is "red" then the only thing that lets you cross the lights is an explicit ATC command to cross the reds as well as general clearance, and that's part of training and procedures because it's a semi-automated backup system to the human primary system. RED MEANS STOP is drilled into everyone precisely to reduce the number of runway incursions/collisions.