>if you're building a new line, you may as well make it high speed; I think the thing to understand here is that mixing speeds is awful for capacity. There are

>if you're building a new line, you may as well make it high speed; I think the thing to understand here is that mixing speeds is awful for capacity. There are some fast trains now, and everything else has to be scheduled around them, which means they each eat up many slots, to clear the line a safe distance ahead. There's lots of demand for more slow trains, which can't be run. If you built a new slow line, you would still have this problem. And the slow trains want to stop many places, so you can't build the line through open fields, and building through towns is really expensive. So you build a new fast line. And then it may as well go a little faster than the existing fast trains. But this increment isn't the main point. Or at least that's my understanding. I don't doubt the price will grow. I have also heard there may have been other not-quite-as-fast options, refurbishing a disused line instead?