Traffic on State Highway 1 north of Wellington ground to a standstill for hours on Friday after a serious crash, reportedly between a car and a van.Emergency services were called to the scene about 4.40pm, and motorists reported huge delays after the southbound lane was closed between the Tawa off-ramp and Glenside on-ramp.Police said one person was seriously injured in the crash.Just after 11pm, the Transport Agency (NZTA) said the road had reopened to southbound traffic.However, it advised drivers to continue to take extra care when travelling along the route.One driver who contacted RNZ said she had "at last" reached her home in Kāpiti about 10.30pm - after arriving at end of Transmission Gully at 5.30pm.She questioned why there had been no notification earlier, so drivers could take the Hutt Valley turn-off and detour instead.Earlier, in an update at 8.05pm, NZTA said the Serious Crash Unit was undertaking an investigation, which would require the road to remain closed to southbound travellers for a few more hours.One stuck driver told RNZ "people seem to be panicking and trying to drive up the shoulder"."They are trying to cut each other off. Seems pointless because no one is moving."Another person said after four hours, some people had started parking their cars and walking away across the motorway to wait elsewhere.Elise Bailey said she had seen more than 20 people, including some with toddlers, walk along the motorway and cross over the median barrier into oncoming traffic."Having to cross across oncoming traffic ... traffic is still moving on the northbound side - people having to cross across with kids in order to get off the motorway."Bailey was one of them, and was waiting at a nearby McDonald's to stay warm when she spoke to RNZ.She said there had been no police cordon turning people away from the motorway at 5.15pm, and no communication from the police while she was waiting."Not one single police officer or any other personnel from anywhere have come down from Porirua on-ramp."She said an update from police "to know that it could be another hour or two before moving" would have provided some relief.Bailey was concerned about how she and others would be able to return to their cars once the traffic cleared."Walking perhaps one or two kilometres along the motorway ... there's no other way of returning to your car."Do you know more? Email news@rnz.co.nz