When the GMC Suburban and the Nova crash at the beginning of the movie, the Suburban would have had to be traveling at a much higher rate of speed in order to stand it up on it's end when it t-boned the Nova.
At one point the four surviving characters are shown driving through the garage in a police cruiser and park it in front of the ramp to block the hybrid in. When they get out of the car all four of them get out at the same time which would not be possible in a real police car because the rear passenger doors of police vehicles are designed without internal handles and can only be opened from outside.
Chicago police uniforms and cars paint schemes don't look anything like the ones in this movie. The cars in this movie have NO state(back plate) or city tags(front windows passenger side). Illinois cop cars don't have standard Illinois plates. They start with the letter M XXXXXXXXX.