The 7.5-mile starter line with 16 stations will offer service at $1 per ride from downtown south to Reliant Stadium, where the NFL's Houston Texans play.
After years of debate and false starts, the rail system under construction since 2001 debuted in ceremonies filled with music and confetti. Outgoing Mayor Lee Brown, one of the system's staunchest supporters, took the controls of the first rail car.
Some people waved as the train passed. Others, with puzzled looks, were getting used to the idea of trains on city streets.
Joe and Leti Cavazos and their two daughters got in line two hours before public rides began.
"It was fantastic," Joe Cavazos said as he got off one of the sleek, silver cars at a downtown station. "The city is not going to move forward without mass transit. The traffic is horrendous. We need trains badly."
The line's debut follows a successful November ballot proposition that authorizes up to $640 million in bonds to start building the rail line's next 22 miles.
Opponents say light rail will do little to untangle Houston's snarled roads because it doesn't reach people who live outside Houston's inner core.
Officials expect light rail to carry 33,000 riders one-way per day, or 16,500 people making round trips — less than 1 percent of Houston's population.
It sure cost them a bundle, but the ticket price isn't too bad, and it does sound like a pretty cool ride.