Kundan Bhagat, 22, of Sonapur, Arariya, was injured when the motorcycle (BR 38 B) hit the bridge after skidding on the gravel. Motorcycle rider Ramesh Bhagat, however, escaped unhurt.
The injured has been taken to BP Koirala Institute of Health Sciences in Dharan for treatment.
The two were on a visit to Hile with 10 other friends.