That is kind of an outdated article. See this thread for the complete story. http://mplsbikelove.com/forum/viewtopic.php?f=9&t=18467

Basically, people living nearby complained about cyclists blowing the stop signs on the trail all time time. The cop was out there to ticket/send a message to people blasting through without even slowing down. I don't think anyone was actually issued a speeding ticket, but the cops were trying to argue that they could if they wanted to. This particular greenway is not part of the parks system and has no speed limit.