The Census Bureau conducts the yearly National Crime Victimization Survey, and every three years, the Police-Public Contact Survey asks the general public about interactions with police. The most recent reports are of the 2011 data, since the 2014 data is not available yet.
In 2011, over 62.9 million U.S. residents age 16 or older, or 26% of the population, had one or more contacts with police during the prior 12 monthsOf those interactions, 42.0% were because of traffic stops (excluding traffic accidents), for an estimate of 26.4 million interactions with police because of routine traffic stops.
Speeding (46.5% of traffic stops) and running a red light or stop sign (6.7%) accounted for a total of 53.2% of traffic stops (see below table). In theory, that's approximately 14.1 million people who had involuntary interactions with police that could be avoided by universal use of traffic cameras (62,936,500 *.420 * .532). That's 22.9% of all police interactions (14.1/62.9) being potentially avoidable.
Cameras, in general, are a non-discriminatory form of traffic control. Nonetheless, the above table does show that speeding accounted for 50.1% of traffic stops among whites but less than 40% of traffic stops among minorities. Therefore, expanded use of traffic cameras would be expected to have a somewhat disproportionate effect, according to race, in reducing interactions with police. Nonetheless, white drivers were 23% more likely than black drivers to think that the police stop for speeding was legitimate (89.6% vs 72.8%).
Given the cost of camera enforcement, the idea of universal camera enforcement is not realistic, but camera enforcement could be used across urban areas to eliminate traffic stops for speeding and red light violations for the majority of the population.
The cost effectiveness of cameras in urban areas is well established (compared to police enforcement), but some people may worry about traffic cameras used as cash cows. A review of traffic cameras published in 2012 by the Transportation Research Board (PDF) addressed this point by recommending that "The law should specify where automated enforcement fine money is sent...[and funds from fines that exceed the cost of operating cameras] should be used for highway safety functions].
The principal public benefit of traffic cameras has always been about improved traffic safety, with dozens of scientific evaluations finding decreases in speeding, collisions, injuries and deaths. Nowadays, given the salience of the Black Lives Matter movement and the increased attention being given to policing, the increased use of traffic cameras should be considered as part of a comprehensive reform to policing to improve safety and promote equal treatment.