A Trail Running Scale

Run-Ability Scale:

This scale ranks how well suited each trail is for running, assessing the terrain, the amount of technical rock climbing, and total vertical gain. 

Surface (1-5): Will I break an ankle?
1:  Buffed out dirt single track, clear of most obstacles (rocks, tree roots)
5:  Finishing the run without a flesh wound is top priority

Technical Scale (Class 1-5): Will I need a rope and helmet?
Using standard climbing classification: Class 1 requires no technical climbing; Class 2 involves some rock scrambling/boulder hopping; Class 3 begins risk of death; Class 4 and 5- I don't even know, I'm scared of heights- it probably involves ropes and helmets

Vertical (1-5): Will I get a polka dot jersey?
1:  100 feet per mile, on average
5:  Ascents average >1,000 feet per mile- hands on knees, unless you are Killian Jornet