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Wednesday was a great day. I had the chance to get on the new and check out some of the hidden features and safety systems.

The new three-acre lid is really taking shape. I was able to walk down what will become the new eastbound direct transit access ramp to the travel lanes. Workers were scurrying about doing all sorts of jobs.

I jumped down to the closed travel lane and back-tracked under the lid to a nondescript door in what appeared to be a solid section of concrete between the eastbound and westbound lanes.

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Inside I found the fire suppression valve room. This is a place that could save your life if there’s a fire inside the lid. The room is filled with massive pipes and 15 huge valves. Each one is responsible for a section of the 800 feet under the lid. Two giant foam tanks fill the middle of the space.

The Washington Department of Transportation’s (WSDOT) Steve Peer was my host. I asked him if someone has to press a button to start the system.

“No,” he answered. “It’s actually a heat sensor that senses heat and where it is and then it applies water and foam to that area so that we can put it out right away.”

The system will trigger as many valves as necessary to handle any size fire.

The foam is environmentally friendly, and the deluge system can be turned off remotely at the

And while WSDOT is still perfecting the mixture of foam and water, it’s the lights inside the lid that are the reason for this weekend’s full closure of the freeway from 92nd on the east side to I-5. These news lights need to be calibrated for safety.

“What we want to do is make sure that the light outside matches the light inside,” Peer said. “To do that, we need to go through under the tunnel and calibrate how the light is at certain lumens for certain different times of the day. Essentially, if it’s a cloudy day, it’s it’s a lot darker. If it’s a sunny day, it’s probably its brightest.”

The tunnel lights, while necessary to light the darkness of the space, also need to match the actual light conditions. It’s so drivers aren’t blinded when they emerge into the sun or see black when they emerge at night.

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“For safety reasons, we want people going into what is essentially a tunnel at the exact same brightness,” Peer said.

This lighting calibration and the upcoming testing of other systems and features highlights that this part of the 520 Project is getting close to the finish line.

“We are in pre-commissioning mode right now, getting ready to make sure, like the lights this weekend, they’re ready to go when we open,” Peer said.

The lid project should be finished this summer. The new direct access ramp to the I-5 express lanes should open a little before that, but that ramp will start as transit only, eventually transitioning to HOV as well.

Both directions of 520 will close at 11 p.m. Friday. The lanes are scheduled to re-open by 5 a.m. Monday.

Check out more of Chris’ Chokepoints here. You can also follow Chris on .Ìý to follow ³ÉÈËXÕ¾ Newsradio Traffic’s profile .