> Google Maps (at least in the US, in my experience) is really great about telling you what lane to be in.

Having recently driven in Boston[1], the problem is that Google Maps tells you what lane you need to be in when the route divergence happens... it doesn't tell you what lane you need to be in to get to that lane.

So I would see guidance like be in the first or second lane (from the left) to make this left turn and all seemed well since I was in the second lane from the left. Then two more lanes merged in from the left and I had to get over two lanes and ended up on a two mile onramp for the highway to New Hampshire.

I see the same things locally, but it's not as obviously bad because I'm familiar with the local highways and also most of the local highways aren't as space constrained so there's almost always plenty of time to merge.

[1] I don't recommend it... we should have driven to the airport and returned our car and taken transit back to our hotel

I need to know what lane I'll need to be in next so I can plan in advance.

Not every road owner in the world has provided how many lanes a road has. To tell you which lane to stay in, it need to know how many there are!

It fails the task as often as not on large East Coast highways. Not nearly as bad on the West Coast.