Here's my advice , first I am not in anyway a lawyer, nor an expert, just offering suggestions based on past experiences with easements.
Step 1: Post a speed limit sign(can be ordered online for cheap enough or purchase from county highway department) and place in the section of your easement that is owned by you.
Step 2: send each neighbor a certified letter advising of the speed limit and explain that if caught horseplaying and damage the road or your property, they will be held liable for any repairs (this way , he can't claim you were singling him out) keep the receipts from when they pick up their letters.
Step 3: record any future behaviors via you camera network
Step 4: if he continues, either contact a lawyer or send him a bill or both.
It's all about putting him on notice. That said be prepared for some retribution and threats. Lock your stuff(if you don't currently).
