That looks like insane amounts of fun.
As to this...
"Cars travelling up the hill in the opposite direction are forced to slam on their brakes as they the trikes speed round corners and cross into oncoming traffic."
Car drivers coming round blind bends on the wrong side of the road is something I've noticed happening with increasing frequency - I've had a few near misses lately, just because some twerp wants to take the racing line rather than slow the feck down for a few seconds.
Yes, these trikers are being a bit stupid, but it's only because they're not car drivers that it's deemed newsworthy.