So where is the largest (near-) vertical drop directly (let’s say nearer than 2m) next to a public road? Bonus points if the road has no guard rails
The Yungas Road is certainly a contender.
Do you mean a drop down TO the road, or down FROM the road? Man-made. or natural? How close to vertical does “near” constitute?
I’ll propose a high bridge, but no bonus for non-guard-rail.
“next to” is ambiguous. From the OP’s mention of “guard rails”, it seems to me that the OP is looking for the farthest drop from the road downwards, and is not looking for situations where the road is at the bottom of the cliff.
Bridges are an interesting idea, but I suspect most will be disqualified by the two-meter limit for distance between the drivable road and the edge of the bridge.
It won’t win the superlative, but California’s Highway One has some nightmarish sections. (The worst segment has finally been abandoned, I hear.)
This would seem to qualify - - YouTube
It’s in Pakistan