A pedestrian is in a critical condition after a crash on the M4 at Margam near Port Talbot.
It happened around 2:15am on Wednesday morning.
Police say it involved a white heavy goods vehicle, a blue Kia Venga and a pedestrian.
Officers are now investigating the road traffic collision at junction 38.
South Wales Police said the M4 at junction 38 is currently closed in both directions and is expected to remain closed for "a number of hours" to allow for investigations to take place.
Officers want to speak to anyone who has information or dash camera footage.
They are being asked to call 101, quoting reference number 2300344929.
Want a quick and expert briefing on the biggest news stories? Listen to our latest podcasts to find out What You Need To Know…