We didn't choose tunneling for those other segments because we didn't have the political will at the time, and in the case of Uptown it was rigged. Back when an alignment was being considered for Southwest the FTA guidelines would provide money for the easiest, cheapest, and fastest alignment. Of course it was only in-theory that the Kenilworth alignment would meet those guidelines, and we've learned the hard way that that wasn't necessarily the case. Just because those other routes didn't have a tunnel doesn't mean no future routes can have a tunnel or an existing route can eventually be tunneled.Again, I'm personally in support of tunnels and if it were up to me way more of our network would be grade-separated. Whatever we spent on a subway would be worth it.This project is already expensive. Granted it would be more expensive with a tunnel, but lets not pretend the Blue Line Extension running almost entirely at-grade would be cheap. There's also an argument to be made about safety; if we built this on West Broadway would it still be possible to make that corridor pedestrian-friendly? The University Avenue Corridor sure isn't, though that's more of an issue with cars than the Green Line, but the light rail is still a barrier along that corridor.I'm always fine with a tunnel, of course, but it's expensive and takes longer and might lead to stops being placed less conveniently to cut costs.
Also, assuming the tracks would be embedded in concrete along West Broadway, is that going to come back to haunt us? There's been rail corrosion issues with the embedded track in the downtowns and along University Avenue.
But I don't think this segment is a particularly strong candidate compared to other places we've chosen to build at-grade. If we didn't choose tunneling for Downtown Minneapolis or Downtown St. Paul or the U or Uptown, what makes it more feasible now? If the answer is that we've decided all those other projects were flawed, and we're now more interested in providing excellent service for urban populations and more willing to pour cash into capital projects, then that's great! We can start with North and also kick off planning to improve existing, more-critical segments. But I don't really see any indication that our politics or leadership are even close to that mindset yet.
And if that's not our mindset, and we're operating under the same priorities and constraints that gave us the existing network, then I don't think the street conditions alone justify a subway. It's an overwide, mostly-straight street in an area that isn't very car-dependant relative to the rest of the region.
As far as pedestrian safety goes, I think a street with center-running trains, improved protected crossings at stations, and one slow lane each way for cars is a strict improvement over the 4+ lane high-speed road we have today, particularly if the LRT is paired with more pedestrian-oriented development (say, some street-facing buildings in existing surface lots).
Regarding durability, I'm not familiar specifically with the issues with existing embedded tracks, but given how common street-running trams are throughout the world, it's hard for me to imagine there isn't an off-the-shelf solution out there.
And again, there's the impact businesses will have during construction. Are we going to disrupt businesses on the north side just to, in theory, have an easier and cheaper route, or are we willing to avoid most of that with tunneling?
Just because there's trams around the world doesn't mean they don't have issues with their embedded track. In our region, road salt and sand certainly don't mix well with embedded rails. And if an embedded rail needs to be replaced that's a long and expensive process.