The collision happened at about 10.35pm on Tuesday when a dark blue Vokswagen Golf was travelling at a low speed along the A6181 Westgate.
Police said the car left the road and mounted a traffic island before colliding with a street sign.
A West Yorkshire Police spokesman today said: "The driver, a man in his sixties from Bradford, was confirmed by medical staff to have suffered a medical episode.
"He was taken to hospital where his condition is said to be stable."
Anyone who witnessed the collision or the movements of the car prior to the collision is asked to contact the Western Area Roads Policing Unit on 101, quoting log 1964 of 11 December.