Johannesburg - The collapse of the pedestrian bridge on the N3 highway in Germiston was caused by a truck hitting the supporting pier of the bridge, the SA National Roads Agency SOC (Sanral) has revealed.The investigations were conducted by the Superstructure Consulting Engineers, the roads agency's acting engineering executive Louw Kannemeyer said in a statement.Kannemeyer said their investigation revealed that the bridge collapse was caused by an impact on the pier in the median of the highway."All evidence suggests that the impact was caused by an 18.1 ton coil of steel that was found lying some 100m north of the collapsed bridge on the N3 northbound road."Marks on the road led directly from the point of impact to the position where the steel coil came to rest."Debris that scattered radially away from the pier that was hit to a distance exceeding 40m confirms an external impact force was of very large magnitude."READ: 4 injured in bridge collapse on N3 highway in GermistonThe incident happened in the early hours of August 9.On the day of the incident, the stretch between Van Buuren Road and the M2 Geldenhuys interchange had been closed.The pedestrian bridge was lying across the highway in both directions.Three trucks and a Mercedes-Benz sedan crashed into the bridge, police said.There were no fatalities.According Sanral the bridge was built in 1978 and has been closed off to the public for a number of years.