It's not NECESSARILY safe. But, it might be perfectly safe, for example, if there were no cars for miles around or if the only cars were on the main route and not on the perpendicular route. I can imagine dozens of other scenarios where this would be a safe maneuver and others have posted some examples. I can also imagine it being dangerous, but only to the same extent any u-turn can be.

My real point is that roads aren't properly set up for bicycle traffic and that sucks. As a result people come up with ways to make it work better and I say go for it, if you can do it safelu. for example, most of the time on one-way streets, it's much safer to ride on the left (due to opening doors, right turners, etc.) but the basic bike laws say you should stay right. I don't care what the law says, because left is safer. (in fact, now many of the bike lanes in NYC on one-way streets are now on the left and I believe there is a provision that allows you to deviate from the bike laws where the law puts you in a more hazardous position that if you do otherwise, but that's just a backup.)