The Arizona Republic is excited about all the riders who flocked to the opening of Houston’s new light rail line, and what light rail might bring to Phoenix. Certainly, thousands of Houstonians did pack the light rail cars. Of course, any product or service has a good shot of getting lots of interest if it’s new, highly promoted and free. The real test begins now that Houston’s free rides are over: Tens of thousands of riders turned out for free inaugural rides on the Main Street line the past four days, filling nearly every train to capacity. But many expect the overstuffed trains could turn into rolling ghost towns today, when the grand-opening novelty ends and the line is put to its intended use of ferrying people to work, school, doctors appointments and other activities. For the next three weeks, trains will operate daily every 12 minutes from 5 a.m. to 10 p.m. The Metropolitan Transit Authority says it will take 35 minutes to travel the 7 1/2-mile route, an average speed (including stops at stations) of 13 mph — barely faster than the average speed of a local bus along the same corridor. Several passengers interviewed during the four-day opening expressed skepticism that people would continue using the train once they have to pay, and said the line’s short distance and slow speeds make it an unattractive commuting option.