Last year during the summer doldrums, we made a quick list of some of the most interesting arcade games that were still unavailable to play via MAME emulation. It looks like that list is going to get one game shorter very soon, since the dumped ROM for Exciting Sonic Patrol Car (roughly "Waku Waku Sonikku Patokaa" in the original Japanese) has been dumped and will be supported in MAME's next official release.
Sonic Patrol Car is simultaneously one of the rarest Sonic games and one of the least interesting to actually play. The barely interactive 1991 arcade game sees Sonic wearing a policeman hat and dodging traffic in a very slow police car (why he doesn't just run at his usual super speed, we can't say). Near the end of the three-minute ride, the player finds Dr. Robotnik in his own hovercar and then mashes the "jump" button to take him down. Sonic & Knuckles it ain't, but it's technically the first Sonic game with (Japanese) voice acting. It's a historical curiosity simply for being an early title associated with Sega's blue mascot.
Unless you were a child visiting certain Japanese arcades in the early '90s, you've probably never seen this game in its original, rocking car-shaped cabinet, complete with steering wheel and turn signals. That bulky cabinet is extremely hard to find in working condition today (even in Japan), even harder to get to someone who could dump the internal ROM data for preservation.