I have to laugh avery time I read another posting saying "never seen this in US". Bicycle freeways this time. Car crazy Los Angeles has had them since at least the 70s, and there is over 100 miles of them now. The LA river trail is parallel to the 710, San Gabriel trail the 605, Anaheim trail to the 55. And there are other shorter ones sprinkled about.

The problem is they are not part of a working network, and security at night is a problem. So they are far from their potential as part of the transit system. Also, exiting such a bike path usually puts you out near freeway ramps, which are crazy places to ride a bike.