.. pure tunnel at a diagonal instead of the "half swastika" would be faster for the trains, that's exactly right. But boring through mud and muck is expensive, which is probably why they are cutting down from the existing street and then covering it up ("cut and cover") wherever they can get away with it.

I've been accused of being a Marxist, yet while Harpo's my favourite, it's Groucho I'm always quoting. Odd, that.