(a) If any police officer of this State or any political subdivision of this State, while otherwise acting within the scope of his authority in enforcing any law, directs the driver of any motor vehicle, other than a police vehicle, to assist him in enforcing that law or in apprehending any person suspected of violating or known to have violated that law, this State or the political subdivision, as the case may be, is liable for the damages or injuries proximately caused by the negligence of the police officer.
(b) This State or a political subdivision of this State may use the defense of contributory negligence and assert the doctrine of last clear chance in an action brought or defense raised under this section.