(Recasts with Cookson interview) By Martyn Herman RIO DE JANEIRO, Aug 8 (Reuters) - Rider misjudgments not Rio's scenic Olympic road race course were responsible for a series of bone-crunching crashes over the weekend, according to UCI chief Brian Cookson. Dutchwoman Annemiek van Vleuten remained in hospital on Monday with three fractured vertebrae and concussion after a horrific-looking accident on the Vista Chinesa descent close to the finish at the Copacabana beach. On Saturday, Vincenzo Nibali, who like van Vleuten was leading the race on the final, high-speed descent, broke both collarbones after he and Sergio Henao crashed heavily on the same stretch of road. More...