More than three dozen people parking at the Ryan Road park-and-ride were reminded last week that the area does not go unpatrolled during Summerfest.
According to the logbook, a total of 40 cars were parked illegally and towed Saturday.
Police officials said the department has to tow vehicles that block emergency vehicle access. An officer is typically at the lot between 3 and 5 p.m. each day of Summerfest.
"Saturday there was a influx of cars that parked illegally at approximately 4 p.m., when an officer was not available to monitor the lot," police Lt. Dave Ashenhurst said.
Any vehicle not parked in a marked stall is ticketed and towed, while vehicles parked on the grass are ticketed, Ashenhurst said.
A Patch reader said in an e-mail that cars were still being towed when he got to his house at 10:30 p.m.
Police Capt. Michael Bolender said some people have ignored the "lot full" signs, which hinders emergency vehicles' ability to answer calls for service.
"If cars are blocking the lanes of vehicle operation ... we are towing vehicles because we have to ensure emergency vehicles can access situations like car fires or medical emergencies that require an ambulance," he said.
If the lot is full, the police department recommends using the park-and-ride at College Avenue.