I didn’t know this question off the top of my head, but I did some digging and found the answer. Yes.

It is illegal to cross the double white lines at all other times unless there is an emergency vehicle running on code (lights and sirens) coming up behind you.

Then you can legally cross the double white lines and give them room to pass. Here’s exactly what the WSDOT says, “Emergency vehicles have complete toll-free access to the lane when responding to a call.

If an emergency vehicle, such as an aid car, fire engine or police car appears behind you in the HOT lane with emergency lights on, you should move to the right and yield to the emergency vehicle, just as always, even if you must cross double white line.”