Why testing for the Green Line Extension is going to take more than a year

Everyone knows that the Green Line Extension is behind schedule. First slated to open in 2018, the 14.5-mile light-rail line into the southwest suburbs has had to overcome a lot of (sometimes self-imposed) hurdles along the way, most notably an intractable railroad and a difficult tunnel project. It’s currently scheduled to open in early 2027.

That’s why I was surprised when I first heard that the light-rail team was going to be conducting testing for well over a year. Testing began a few weeks ago, in fact, and will extend all through 2026. 

My first reaction was this: “Why do they need to test it so long when it’s way behind schedule?” I put the question to Metro Transit officials, and after some discussion, I’m happy to share what I learned. It turns out the long testing timeline is a feature, not a bug.

Green Line tunnel construction

First, though the tracks are technically in place, construction isn’t yet complete for the project also known as Southwest LRT. The most complicated feature, the Kenilworth tunnel under the Minneapolis chain of lakes, is still being built. For example, the tunnel includes “jet fans” designed to quickly remove air and smoke in case of an underground fire. Those have not yet been fully installed, and it’s complicated.

“Those facilities in the tunnel are kind of new, different from what we have down at the airport,” said Jim Alexander, project director for the extension. “That’s something new to our organization, and we have to ramp up. The testing is going to be a key piece to get there.”

Because of the tunnel, the agency and contractors are testing the east and west ends of the line while the center tunnel segment remains under construction. This is why route equipment is being tested in stages. Rather than a sign of procrastination, the long timeline reflects the fact that the agency is getting a jump on things. Starting early along both ends, rather than waiting until the entire route is complete, allows planners to speed up the painstaking process of testing almost 2,000 pieces of equipment.

Related: A tale of two Green Lines: 10 years after ‘Central Corridor’ light rail transformed University Avenue

That said, there were hurdles even in areas where the tracks are already completed. For example, doing “deadwire testing” on the western end of the line (so-called because electricity is not yet turned on) presented a logistical challenge. Metro Transit purchased a bright red “shuttle wagon” — a tracked vehicle that can pull the trains back and forth for testing or maintenance purposes.

The alternative, transporting light-rail vehicles on trucks into Eden Prairie, was challenging given the 100-foot length of each train. Instead, the agency opted to purchase the shuttle wagon, which tugs the train along behind it and could be handy in case of any future power losses.

Here’s a short and partial list of 1,500 things that need to be checked out: warning signals, gate arms, monitors, tension wire arcing, contact wire tension, ballasts, and no less than seven areas with “crossovers,” which are switches that allow trains to cross between tracks in case of an incident. In each case, every piece of equipment has to be checked out individually.

Imagine the job of the LRT operator doing the testing procedure. You’re not driving the train in operation, speeding between stations; instead, you’re pausing and moving forward over each little switch and sensor, and then doing it all again in reverse to check out all of the crossovers. Each switch and signal needs to be tested multiple times, and the process seems like a repipe for tedium.

“Its a different type of mental engagement to be part of that whole process,” said Brian Funk, the agency’s chief operating officer.  “We’ll be working to do the sequence of the testing in the perfect order. It’s a great way to provide valuable feedback to the team.”

One more example: The Green Line Extension has 20 substations that convert AC power from Xcel Energy into DC current to power the light-rail train. The power runs from the catenary contact wire down though the train’s pantographs, and provides electricity to each of the traction motors. 

To test these systems, the train has to be run at “crush load” capacity (technically termed AW3), which means that the agency has to find a way to fill the car with the weight equivalent of a Vikings crowd. Various agencies try different mechanisms — Seattle’s Sound Transit used jugs of water for its LRT vehicles, which eventually adds up at 8 pounds a gallon. 

For the “Central Corridor” Green Line, the agency had spent hours loading the vehicles with steel plates to equal the weight of hundreds of transit passengers. Alexander subtly referred to this as “a lot of labor,” and I shudder to imagine the literally Sisyphean process of stacking the steel plate equivalents of six hundred people. 

This time around, they simply ran four-car trains along the route (three cars are the normal maximum), and drew maximum current through to the engines to stress test the power with the extra vehicle weight. It was apparently exciting to be in the substation when the power hit peak capacity and the electric transformers handled the load.

“That test is pretty cool,” Alexander said. “You’re in the traction power substation with a lot of components, and really trying to stress the traction power [all the way] to the maximum loading that the traction power would see.”

The ‘foam finger’ test

Another fun example: agency crews attached “foam fingers” to the outside of the vehicles to ensure that there was an adequate dynamic envelope between the train, the stations and the adjacent infrastructure. (The “dynamic envelope” is the space that the train is normally permitted to sway or rock as it moves.) If the fingers made contact with anything, then something had gone wrong and technicians needed to fix it.

(I liked to picture the agency using those “#1” Vikings foam fingers for this test; they did not send me a photo, so I suppose it’s possible.)

Technically, the light-rail track is still under the purview of the construction contractor, overseen by Alexander and the construction contractor. After their testing is done, the line will be officially handed over to the agency, and official Metro Transit testing can begin in earnest. That will be a big day.

“It’s going to be a monumental occasion when we do that testing run that navigates us to Target Field out from the Southwest stations,” Funk said. “One pull, and to be able to go and experience the entire thing in one fluid back and forth … that’s going to be huge.”

In the meantime, there’s going to be a lot of back and forth and back and forth and back, in short little chunks between the nascent stops. It’s a tough job, but somebody’s got to do it. I suppose I can wait after all.

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