A blue Yamaha bike, a silver Audi A3 and an ambulance crashed at the crossroads with the A644 Brighouse Road in Sandbeds.
It happened at about 10.30pm on Monday, March 26.
The bike and Audi had travelled from the Shelf side of Brighouse Road when the crash happened with the ambulance, which was travelling towards Bradford.
All vehicles stopped at the scene.
Emergency services arrived and the motorbike rider, a man in his twenties, was taken to hospital with serious injuries.
He remains in critical condition today.
Police have asked anyone who witnessed the crash to contact the Safer Roads and Neighbourhood Support team on 101, quoting log 2073 of 25 March.