I've often said in Ottawa, when people were wringing their hands about the impossibility of an east-west light rail line, to just run it down the middle of the Queensway.
In Los Angeles, that's sometimes what they do with public transit. The photos below are of bus lanes and stops on the 110, a busy north-south freeway in L.A. There's a light rail line that runs down the middle of a highway in Pasadena as well, I've used one of those stops as a rider and it's a pretty strange experience, to be on a platform waiting for your train, wedged in the middle of a 10+ lane highway. Not exactly restful... but the routes are certainly efficient. I'll have to try to get pictures of that one if I am out that way again.
Don't worry, I was a passenger for these photos (which is why it's taken from the carpool lane), I would not click and drive on an L.A. freeway! Car is heading north towards downtown.