Some more thoughts about the risk taking: that inevitably happens to everyone, even the least reckless. Magnitudes certainly differ, but it's always far from gone. Because when cycling, the brain unavoidably enters a state that would be called hypermiling if it happened while driving. The bad thing about stopping or slowing down isn't so much the time lost, it's the exertion required to get going again. And that logic does not just happen on the conscious level, it's much deeper. You'll hate applying the brakes even if, on the conscious level, exertion is the only goal of the ride because you're not going anywhere but doing a workout. "Stopping leads to exertion, don't stop" must be some preset circuit in our brains that has been there since before bipedalism. It's certainly also noticeable when driving (we hate the red light even when not in a hurry at all) but it's much stronger when the exertion isn't just a gentle touch with the right foot.

Back to that straight tunnel from the picture: something like that is extremely rare, because bike roads are rarely built completely separate from other roads and when they are not separate, the descent/ascent parts inevitably get folded into wherever they fit.

In theory (but not always in practice) the steepness of the road accessing the underpass should be within the limits stated for the type of road (so - again in theory - not too steep).

A good example of how NOT to design an underpass (very steep AND curve in the middle), this is Florence (Italy):

https://www.google.it/maps/@43.7754979,11.2351912,3a,75y,53....

But they did put on a sign to prevent pedestrians to access it, so the mugglers won't go hiding there ;).

At first glance that underpass didn't seem that steep, but then I went to look for the underpass which I feel is super steep, I realized, maybe it's just difficult to get a good sense of the steepness from streetview.

Here's one I've gone through and feel is a rather dangerous one: https://maps.app.goo.gl/pU36XG6J89QL2nqJA

The view is from top of the underpass, but if you look to the back left you can see there's a downhill and then a really sharp 90° turn which might lead to really dangerous situations due to poor visibility and high speed.

Yes, streetview does not convey the actual situation, in person it is steep (though I have seen steeper ones).

That underpass is just after a bridge (over the river) so they couldn't make it less steep by making the ramp longer, but the cyclists (those that know the area) can turn on the right right before the ramp and use the "normal" roads/streets, someone that isn't already familiar with it is taken by surprise.

This view from a bit further renders a little better the situation:

https://www.google.it/maps/@43.7752485,11.2348264,3a,75y,22....