The gang tried to rob an old woman by offering her lift in their vehicle on Moga-Ludhiana road. The woman, however, raised an alarm following which bystanders caught hold of the four and handed them over to the police, an official said.
Preliminary investigations revealed that the gang had committed several robberies on the highways using the same modus operandi, he said.
The four accused have been booked under relevant sections of the IPC, police said.