I wish the article had made the details more clear, because I have trouble understanding.
1294 - 1112 = 182 drivers' licenses were not checked. Why? And, how did they check licenses with just "a slowdown?"
18 + 13 = 31 drivers with citations or jail. Only 12 cars were impounded. How did the other 31 - 12 = 19 cars get away? Were there licensed passengers in them?
Unfortunately, the undocumented drivers here do that (drive unlicensed) more than the natives," Hahn said. "If they've been involved in an incident, they flee because they don't want to deal with immigration."
Unfortunately, this type of enforcement (which is a burden to citizens and might be construed as an infringement of liberty) may become more necessary if they don't enforce immigration law. Even illegal aliens with drivers licenses may flee accident scenes because they "don't want to deal with immigration" or be discovered to be driving without adequate insurance. (It's not that hard to get a license legally.)
Maybe the FedEx guys, etc. were given a pass because those companies keep a tight check on their drivers?