Emergency services responded to reports of a collision on Leeds Road in Huddersfield on Wednesday evening.
A silver Ford Transit van left the road and struck a wall in the area near UK Superbowl at approximately 8.07pm.
The male driver, aged 58, was initially treated at the scene before being transferred to Leeds General Infirmary.
His condition was described as critical.
West Yorkshire Police officers attended the scene and are continuing with their investigation into the circumstances of the incident.
Investigators believe the driver may have experienced a medical emergency while operating the vehicle.
Detectives have appealed for anyone who observed the collision or who may have seen the van prior to the crash to contact them.
Officers have also requested that any dashcam or mobile phone recordings of the incident be shared with police.
Those with information should reference number 13260526688 when making contact.