I have thougth up a system where there are sensors on a trailer that detect vehicles to the side of you.
WHen you turn on your signal for a lane change your in cab indicator would flash red if there was a vehicle next to you. WHen it's all clear and there is nothing to your side, it would flash green.
I thought of this a few years ago when I was SICK of truckers running me off the road because they couldn't pass properly.