M50 flyover barriers are not designed to stop head-on collisions, Transport Infrastructure Ireland (TII) has said after a car crashed through one and fell down on to the motorway on Wednesday.Concerns were raised in the aftermath of the crash as to how the vehicle was able to breach the safety barrier and land on a traffic lane underneath.The State agency responsible for the road network said the barrier, which is standard on many other flyover bridges, was designed to deflect glancing crashes by vehicles travelling at relatively low speeds.An industry source said incidents such as Wednesday’s were “rare” and that the safety infrastructure in place was sufficient to stop the vast majority of incidents likely to take place on the road. The couple were driving from Dublin Airport southbound on the M50 when they exited the motorway at Junction 10, near the Ballymount slip road.The vehicle, a source said, mounted the footpath at “extreme velocity”, crashed through the metal and mesh barrier, and travelled a significant distance in the air before landing bumper-first on the embankment beside the motorway.The car then bounced over the external crash barrier into busy lanes of traffic at about 3.20pm.The distance the car travelled once it broke through the flyover parapet has led investigators to believe the electric vehicle accelerated quickly as it left the motorway exit ramp.Gardaí are investigating the possibility that driver error led to the car rapidly crossing the R838 or the possibility that a medical emergency was responsible for the loss of control.The couple were removed from the scene and brought to hospital to be treated for serious injuries. Their condition is not known. TII – quoting an infrastructure specialist – said the barrier on the M50 flyover bridge in question was “not designed for head-on collisions”.The State agency said the “vehicle road restraint system” in place on the bridge, the barrier, was instead “designed to absorb impact energy and redirect cars striking at shallow angles”.The 1.8m high containment parapet, TII said, was standard design in Ireland for similar flyover bridges.The barrier is designed to deflect crashes with an angle of impact of no more than 20 degrees – a similar angle to the head of a pencil – of a 1.5 tonne vehicle travelling at no more than 80km/h.“Higher containment levels are used in certain situations, depending on such factors as vehicle speeds allowed and bridge geometry,” TII said.At one point in the aftermath of the crash, the southbound queue of the M50 motorway stretched back to junction one for Dublin Airport during rush hour.