When I teach Vehicle Operations in the Basic Law Enforcement Academies, I tell the recruits that the second police vehicle through the intersection during a priority run or pursuit is not the safer one; rather it is the more dangerous place to be. Drivers hear the sirens and see the patrol car go through and then assume the coast is clear. They are not looking for and often do not hear the second responding unit.
The second police or sheriff's vehicle, who is probably calling out the pursuit to enable the first unit to concentrate on being primary depending on local agency policy, should increase his or her reactionary gap, slow down and, when appropriate, stop.
I also tell them to change the siren tones to differentiate them from the primary unit (two tone as opposed to the primary unit's yelp or wail tone), and (very importantly) to turn their head from side to side. This action allows them to visually clear the intersection and break any tunnel vision that they may have developed while fixating on the unit ahead of them.
Additionally, the first unit should keep rotators going in their light bar, but deactivate any rear facing flashing emergency lights that could blind the officer in the second car. Those rear facing flashers can be deadly for the following police officer or deputy sheriff at night, in fog, or on a dirt road.