According to Yonah Freemark, "Green Line trains [between Minneapolis and St. Paul] are taking up to an hour to complete their journeys, and even optimistic schedules released by the local transit agency put running times at 48 minutes, or less than 14 mph on average." Other light rail lines failing to light up anybody's radar gun: Houston's North Line, with an average speed of 17 miles per hour, and Los Angeles' Expo Line, with an average speed of 18 miles per hour.
Freemark makes the following argument about how travel times negatively impact the adoption of public transit: "With speeds like those light rail lines or services like the Silver Line, it’s little wonder that it’s so difficult to convince people to get out of their cars in so many places. The fact of the matter is that services like this often do not provide much mobility improvement over the bus services they replace. That’s particularly true for large regions where too many destinations are simply too far away to be accessible by transit that averages such slow speeds."
For comparison, Freemark goes on to detail the ambitious, $35 billion Grand Paris Express program, which "will completely alter the landscape of this large metropolitan area…"