Don’t ever let this happen to you!  Really know the dynamics of roads you’re planning to ride.  It’s been a while—years in fact since I deliberately put myself in a life threatening road situation. 
In Bar Harbor I made a terrible mistake and rode a section of road that I knew to be dangerous just to save 20 minutes. Rather than taking the 5 mile rural loop back to the barn this tired horse chose to ride a mile stretch on Route 3 a major highway.  That mile stretch is as narrow as any rural two lane country road without shoulders but carries a lot of traffic and all of it fast. I’ve driven it hundreds of times without realizing how steep the grades are in a couple of short sections. I never thought about it because I didn’t think I’d ever be dumb enough to ride a bike on it.
Even worse: something totally unexpected. The tarmac on this section features imbedded gravel extending 3 feet into the roadway making it impossible to avoid.  It caused my thin, high pressure road tires to slip and slide under the pressure of a steep grade.
The going was excruciatingly slow while 18 wheelers, dump trucks, UPS and Fed Ex all flew by with little room to spare.  It was a horrible few minutes but did provide me with an inadvertent chuckle that wearing a helmet would be mentioned in my obit proving even terminal stupidity can be accomplished with a modicum of correctness.