The bus was carrying students of Millat Public Grammar School of Faisalabad who were returning from an excursion to Kalar Kahar, about 200 km from Lahore. The accident occurred on Sep 26 near Chakwal city.
A spokesman for the traffic police said the driver lost control of the bus when he was negotiating a turn on the motorway between federal capital Islamabad and Lahore. Senior police officer Malik Ehsan said the accident occurred due to brake failure. Local media reports also blamed overloading and poor light for the accident.
Police and rescue service officials said 37 people, most of them students, had died in the accident. Over 20 people were seriously injured and some of them were taken to a military hospital in Rawalpindi.
Though the bus had a capacity of 72, it was carrying 110 students and teachers in violation of traffic rules, police said. This was one of the worst road accidents in years, they said.
The students had gone to Kalar Kahar and Khewra, two popular tourist destinations, for an excursion and a picnic.
The accident occurred when they were returning home. Local residents said there had been several accidents in the same area in the past.
Police and rescue workers had to cut the mangled wreckage of the bus to pull out bodies and the injured. Officials said an investigation would be carried out against the school�s management to ascertain why they violated rules by packing 110 students and teachers into the bus.