[jarek]

This seems like as good a forum as any... what exactly are the rules for two-lane roundabouts? From which lane is it okay to exit? If you're in the inner lane and want to exit onto the left lane of a four-lane road, do you have to watch out for people in the outer lane, or do they have to watch out for you?

[Nick_C]

I won't talk about left and right because I'll get confused.

If you want to exit after 90 degrees, outer lane. If you want to exit after 180 degrees (straight through), either lane. If you want to exit after 270 degress, inner lane at first, then start indicating you are exiting, perhaps moving to outer lane before exit. The latter sounds confusing, in practice it isn't, mainly because other people will be expecting it.

[jarek]

It didn't even occur to me that left and right lanes get confusing. My apologies.

My confusion about the multi-lane roundabout mostly stems from the scenario where two cars, entering from streets 90* in the direction of the flow apart, both want to go straight through. If the one entering 'upstream' takes the inner lane and the one 'downstream' takes the outer lane, it would seem that in some timing conditions you'd get a collision situation when the inner lane car tries to exit but must cross the outer lane to do so. Is this a practical concern? Is there a universal set order of precedence for this case, e.g. inner lane always yields if necessary?

[Nick_C]

You have the additional rule that everything gives way to traffic already on the roundabout, which (in practice) means that particular timing event doesn't occur. The downstream car cannot enter the roundabout until the upstream car has gone past, or it can enter only if the upstream car is too far upstream and is not a threat. In either case, there is no collision.

In places I've driven where there might be confusion, they mark the lanes with arrows to show which ones are exiting and when.

They work pretty seamlessly in my experience. You only have to look one way (upstream), instead of two, to judge whether to enter the intersection, and you don't have the time-waste of traffic lights.