PHOENIX - About 235,000 drivers travel through the I-10 Deck Park Tunnel in downtown Phoenix every day. Even if it's part of your route to and from the office, there's a side to it you probably haven't seen, until now.

To access this secret side, you would first start out in a parking lot near Margaret T. Hance Park. There are two doors and stairs that lead to a hidden tunnel inside the tunnel.

"It’s definitely interesting down here," said Bob Cook, highway operations tech supervisor for the Arizona Department of Transportation.

You have to be careful which door you open in his office. "On the other side of this door is I-10 eastbound," Cook said as he gave 12 News a tour inside.

You wouldn’t know it, but just about every time you’re stuck in a traffic jam in the tunnel, huge fans are fired up for your safety. The hidden hazard is carbon monoxide.

"We have eight fans and four vent rooms," Cook said. "On low speed, they’re 250 horsepower and on high speed they’re 700 horsepower." That’s about the same as a Ferrari!

The fans turn on automatically any time a sensor in the tunnel is triggered, completely clearing the air in less than five minutes. They can also be manually controlled, if Cook and his team think it's necessary.

"When carbon monoxide is high, we blow fresh air into the tunnel and then the carbon monoxide goes out the ends," Cook said. "During a fire, we turn the blades into exhaust and turn them into high speed and it clears the tunnel really quick."

There are sound attenuators that keep the nearby neighborhood from hearing the noise of the fans kicking into high gear.

And in another secret room beneath Central Avenue is the control room which was ADOT's first Traffic Operation Center in 1990.

"Everything from the vent rooms, comes into here and we can control it from either the P.C ... or our old antique board," Cook said. "This was the original board that they manually controlled all the fans, lighting, everything.

"The tunnel was a stepping stone for future freeway management systems and intelligent transportation systems and everything that's now gone on into the new Traffic Operations Center."

Today's 'Central Control Room' underneath Central Avenue was 1976's 'Traffic Operations Center.' ADOT outgrew it quickly.
Today's 'Central Control Room' underneath Central Avenue was 1976's 'Traffic Operations Center.' ADOT outgrew it quickly.