Higher visibility, such as through vests, SHOULD work, but it doesn't. Look around. People wear vests on the ramp and still get hit by bag tugs and caterers (and yes it HAS happened). Midairs still happen even with flashing beacons and strobes. Police still get hit when they have someone pulled over on the side of the road, people don't see school busses with the flashign red lights and pop out stop signs... Vests only work when people are looking. Of course if people were looking you wouldn't need vests...