The young man was spotted lying on the ground just before the Rolle junction by a driver heading towards Geneva at around 3.45am, said Vaud police.
The driver stopped and called emergency services. On arrival, they found the teen had a broken ankle and wrist. He was taken to hospital in Morges.
Police discovered a broken rearview mirror at the scene and presume the youth was hit by a vehicle.
Anyone with information should contact police on 021 333 5333.