Police are trying to trace drivers they believe may hold vital evidence about two crashes in which three people died.
A taxi driver and one of his passengers died after a head-on collision on the A692, in Consett, County Durham, on Sunday evening.
Imran Yaseen, 24, from Middlesbrough, died in a car crash on the A1M about two miles north of the Carville junction on 12 May.
Police believe passing drivers in both crashes could help their inquiries.
Taxi driver Michael Stewart and one of his passengers Michael Murray, died in the head-on collision with a Citroen Xantia on Sunday evening.
Hard shoulder
Mr Murray's wife Margaret, who was with her husband in the back of the Peugeot 406, was seriously injured and is still in a critical but stable condition in hospital.
A third passenger, a man in his 50s, is also stable in hospital, as is the other car driver, a 26-year-old man from Consett,
A Durham Police spokesman said detectives had established that before the collision, the Citroen had overtaken a Mercedes.
They believe the male Mercedes driver stopped but did not leave his details. They are asking for him to come forward.
In the other collision, Mr Yaseen, was a passenger in a car which collided with a trailer parked on the hard shoulder of the A1M.
Investigators believe two lorry drivers heading in the same direction may have witnessed the crash in their rear view mirrors. They are appealing for the drivers to contact them.