A PA31 pilot making a night takeoff from YIP experienced a conflict with a ground vehicle which failed to exit the runway.

Narrative

[I] called YIP Tower for clearance and taxi. Runway 5R was in use; but I requested Runway 27. (This runway was much shorter taxi time and also set me up on a perfect heading for direction of flight. Wind was calm.) Tower told me to taxi to Runway 23L Intersection G. After I read back my IFR clearance; I again asked if 27 was available since he did not acknowledge my request. I was told it was and to taxi to it.Once holding short; I called ready. A few moments later; Tower asked me if I was ready. I acknowledged; and was then cleared for takeoff. I scanned runway upon entering and saw nothing out of the ordinary. On takeoff roll; I heard Tower say something to the effect of 'Electric ##; remain clear of 27.' I figured he was telling a utility vehicle to stay clear of the runway while it was in use. I could not hear the vehicle's response because they were on a different frequency. I then heard Tower say something like; 'Electric ##; clear Runway 27 immediately!' By this time; I had started rotation; and noticed a pickup truck vehicle pulling off of the runway onto the grass.Tower never did say anything else to me about the situation once I was in the air. I was simply told to contact Departure. There was nothing else that could be done on my end to prevent such an occurrence as this from happening. The vehicle was pointed away from me; so I could not see his headlights; and the taillights of the vehicle simply blended in with all the runway lights. By the time I realized there was a conflict; the safest thing for me to do to eliminate the hazard was to continue rotation and get off the ground and away from the vehicle.Looking back on the situation; it definitely seemed that the Tower Controller was distracted or something to that effect. The fact that he missed both my initial request for Runway 27 and my call that I was ready for departure was unusual. My only other suggestion to remedy conflicts like this is to make sure that airport vehicles understand they should be listening to all transmissions that the Controller is making; even if it's not to them. At this time of night; the Tower Controller was working all frequencies. So his takeoff clearance to me was most likely transmitted on Ground frequency as well. The airport vehicle should have heard the takeoff clearance for the runway he was currently on and alerted Tower or cleared it himself.