I spoke with a Lieutenant with the U.S. Park Service police today. My intent was to find out how to get access to their records, to see if the police who'd been issuing citations had cited any cars that day, or if they'd just cited cyclists.

The lieutenant was actually pretty willing to hear me out and very candid, and he basically said that it is their right to selectively enforce the law like that. Nonetheless, I'm going to contact a few other people/institutions in an effort to verify what he told me.