It's a must anyway, we drove down from Rome just to see Vesuvius and Pompeii. Road to the top from Ercolano is not very well marked, better near Ercolano and less as you go up, but the locals know the road and you don't need to be fluent in Italian to get pointed the right way. It's just a bit twisty, nothing like a drive up a mountain pass, but if anyone in your car gets car sick easily drive slower than posted and take it easy in the curves , As this is not a road most Italians take, you shouldn't be honked and yelled at for daring to drive under the speed limit. The hike once you reach the parking lot is about 20-25 minutes on a loose-soil path, so tread carefully and stay away from the edge. It would be better walking in hiking boots, but I got to the top in old sneakers and I passed a lady who was managing well walking up in high heels. Take it easy walking on the way down, I was passed by a guy running down who made it to the parking lot just fine, but on loose soil like that you're asking for trouble if you go too fast.