The driver, a 52-year-old man from Bradford, is believed to have been taken ill at the wheel before crashing into a lamppost in Dewsbury Road, Tingley, just after 8pm last night (Thursday).
Paramedics pronounced him dead shortly after arriving. Enquiries are ongoing.
Eyewitness Toby Barker said: “I was on Tingley Roundabout oat about 10pm and Dewsbury Road was closed both sides with police tape.
“There were lots of police cars on the left hand carriageway with blue lights flashing. I could see a lorry that looked like it had jack-knifed.
“I thought it must have been serious because an officer was taking pictures and both carriageways were closed.”
Any eyewitnesses should contact the Major Collisions Enquiry Team on 01924 293047.