as we continue to run this post off topic.....lol
I've run beside people at 80mph in a 55 two lane (clear conditions/traffic) and barely been able to get past them. They seemed to think they too had a reason to be going that fast. Rarely does a call justify that fast of a response tho, in my opinion. Adrenalin gets the best of everyone on occasion, but the younger kids seem to be more susceptable.
As far as a radio for your travels in michigan, that corridor of Michigan has numerous counties/dispatch centers. And I believe most, if not all are either trunked or going trunked. I'm not sure, but I believe this limits your ability to just introduce a radio into the system. React still had some folks in the monroe/downriver area, so GMRS might be possible. Even a ham license would get you to a local repeater, but you may have a difficult time getting a response. (I'm not familiar with the specific area you talk about, it may have great repeater listeners.)
Me, the times i've been without my cell or poorly covered, I grab one of the umpteen stander-bys cells and talk to dispatch. Not that it will do a lot of good. Passed an overturned car one day, stopped, assisted with getting the gentleman out (against my wishes..he insisted) and into a passing cars back seat. Used the drivers cell to call dispatch in the area, and tell them fire/ems could slow down, but continue. They got the message, but the trooper who showed up at 120mph apparantly hadnt, and basically snarled at me for her not knowing...