There are some quite narrow bits, and some 'overhangs' where the rock overhangs the road, so take it easy, toot on bends, and set off early in the morning to avoid the worst of the traffic. However, in high season, lots of coaches take this road, so it must be perfectly passable.
It's a fantastic area - lots to see and do. Whilst you're there, turn left at Le Rozier, and go up the Jonte to see the vulture centre at the Belvedere de Truel - on a warm day you'll see loads of vultures flying to and from the cliffs and over the valleys.