If it feels like a long time ago that Seattle was debating how to replace its broken down waterfront viaduct—that’s because it was. Governor Christine Gregoire signed a bill authorizing the removal of the Alaskan Way Viaduct and the construction of a massive deep-bore tunnel in its place way back in 2009. (She did so over the objection of Seattle mayor Mike McGinn, who had been elected on a platform of opposition to said tunnel.) 

Just getting to that point was a long and painful process. Building the tunnel itself took even longer and cost, well, a lot more money. But those are, ahem, sunk costs. The tunnel is now (finally) a part of our lives. And with it, bright white walls painted with enormous green stick figures and arrows telling us precisely how many feet we are from the nearest emergency exit doors. 

At their worst, those giant green figures, which look kind of like they are in a dead sprint, are a constant reminder that something could theoretically go wrong inside the tunnel. At best, they are a comforting reminder that if something does, travelers have a contingency plan.

The two-mile tunnel has 16 exit doors, spaced out 650 feet apart on the west side. (That’s on your right if you’re driving south, and on your left if you’re driving north.) The tunnel walls conveniently also tell you how close the nearest exit is. But the tunnel is deep underground (more than 200 feet below grade at its lowest point). So where the heck do those doors lead?

Well, they don’t just lead to ladders allowing you to pop out onto the street through a manhole cover like a Teenage Mutant Ninja Turtle taking a night off. Instead, the doors, which are fireproof, lead to long hallways, complete with benches, and their own ventilation systems. Those hallways, in turn, can lead evacuated travelers to maintenance buildings on either side of the tunnel. 

But please, unless there’s an emergency, take our word for it. Each exit door is also hooked up to an alarm that will sound if opened.