Quite a lot of cars have lane assist now, where they will have a light on the wing mirror if there is something in your blind spot.
They also vibrate the wheel if you go over lanes and aid in steering your back.
I imagine this is a combination of the two. My worry is how it deals with something like this http://www.op-online.de/bilder/2012/12/18/2669673/1360212316... Does it just stop?
Not sure exactly how this will work: will the car change lane immediately (or just a few seconds after you turn on the signal) or will it first make sure that the driver behind you won't close the gap? Because if it doesn't do the second thing (i.e. making sure that the driver behind you will let you change the lane) then I'm not sure how it will work in cities with crazy traffic.