Police say a 58-year-old man died after falling from a bridge over the M5 on Wednesday morning.
The motorway was closed in both directions as emergency services dealt with the incident between Wellington and Taunton.
Police were called at around 8am when it was reported a pedestrian had been struck by at least two vehicles.
The northbound carriageway was reopened around noon but the southbound direction remained closed during the afternoon.
Police appealed for information from witnesses who may have seen the incident, or who were travelling at the time along Honiton Road which goes over the motorway.
Traffic was diverted via the A38, leading to heavy congestion around the area.
A police spokesperson said: “We are appealing for witnesses after a fatal collision on the M5 this morning (Wednesday 28 December).
“We were called to the M5 between junction 25 (Taunton) and junction 26 (Wellington) at around 8am following reports of a pedestrian falling from an overbridge, and was subsequently struck by at least two vehicles.
“Sadly, the pedestrian, a 58-year-old man, has been pronounced dead at the scene.
“The next of kin has been informed and our thoughts are with the family at this time. They are being supported by a specially trained officer.
“The M5 northbound was opened at around noon. The southbound carriageway is still closed.
“Officers are now appealing for witnesses who may have been travelling on the M5 between junction 25 and 26 or along Honiton Road, which goes over the motorway, around the time of the incident.”
Witnesses are asked to call 101 and give the call handler the reference number 5222308019, or complete our online appeals form.
You can contact the independent charity Crimestoppers 100 per cent anonymously on 0800 555 111 or via their Anonymous Online Form.
No personal details are taken, information cannot be traced or recorded and you will not go to court or have to speak to police when contacting Crimestoppers.