So a big part of the question here is where was the truck heading and is it reasonable to believe that if not stopped it would end up colliding with innocents.
(c) A peace officer is justified in using deadly force against another when and to the degree the peace officer reasonably believes the deadly force is immediately necessary to make an arrest, or to prevent escape after arrest, if the use of force would have been justified under Subsection (a) and:
(1) the actor reasonably believes the conduct for which arrest is authorized included the use or attempted use of deadly force; or
(2) the actor reasonably believes there is a substantial risk that the person to be arrested will cause death or serious bodily injury to the actor or another if the arrest is delayed.
(a) A peace officer, or a person acting in a peace officer's presence and at his direction, is justified in using force against another when and to the degree the actor reasonably believes the force is immediately necessary to make or assist in making an arrest or search, or to prevent or assist in preventing escape after arrest, if:
(1) the actor reasonably believes the arrest or search is lawful or, if the arrest or search is made under a warrant, he reasonably believes the warrant is valid; and
(2) before using force, the actor manifests his purpose to arrest or search and identifies himself as a peace officer or as one acting at a peace officer's direction, unless he reasonably believes his purpose and identity are already known by or cannot reasonably be made known to the person to be arrested.