The road is a good one, but I would not recommend self-driving from Marrakech to Essaouira at night. There is a toll highway for part of the route, which is straight, lit and safe. However, you still need to take the national road for part of the way. Personally, I hate taking that road at night and my friends are experienced drivers. It’s not lit and as a result all on-coming traffic blinds you will lights on full beam. In a state of semi-blindness it’s easy not to spot other road users… Not only do donkeys not have lights – neither do bicycles, dogs, cars or old men in jellabas. I’d recommend having a decent night’s sleep in Marrakech and don’t set off too early or you’ll get stuck behind trucks in market towns all along the route. Look out also for the police with speed cameras. Safe journey!