It’ll be at least three years before North Texas residents ride TEX Rail trains between downtown Fort Worth and DFW Airport, but a significant worry has come to light about the rail cars planned for that ride.Star-Telegram transportation writer Gordon Dickson detailed those worries and the background discussions of them among local transit officials in stories published in the newspaper Saturday and Sunday.Officials of the Fort Worth Transportation Authority, the T, say they are well aware of the problem and will screen for it when they begin taking proposals from manufacturers offering to sell them cars for TEX Rail. That could happen by the middle of 2014.It’s reassuring that those officials promise diligence. Still, the history of plans to use this kind of car — a choice made at the insistence of Dallas Area Rapid Transit, which owns much of the track on which TEX Rail will operate — has long been worrisome.At times the cars, called diesel mobile units because each one is powered by its own diesel engine rather than being pushed or pulled by a locomotive, can lose their essential electrical contact with the rails on which they ride.When that happens, the train can fail to trigger crossing warning gates and lights, a clear safety hazard for passengers and motorists.The train can also disappear from dispatchers’ computer screens, raising the danger of two trains being allowed on the same tracks headed in opposite directions.The electrical problem, called shunting, has been known in the rail industry for some time. It happens because the DMU cars are so light that their wheels don’t rub rust and other buildup off the rails like heavy locomotives do.The Denton County Transportation Authority uses DMU cars on its A-train between Denton and its connection with DART in Carrollton.In August 2012, an A-train lost its electrical connection near Lewisville’s Hebron Station and disappeared from the dispatcher’s screen for about 10 seconds. The incident alarmed a Federal Railroad Administration inspector, who wrote a letter to DCTA about it.Since then, the authority has sent crews out on the tracks three nights a week, driving special vehicles that scrub the tracks.That’s not exactly a 21st century approach to a crucial safety problem. Let’s hope that the manufacturers who come calling on the T next year can be a little more reassuring about fail-safe measures.There’s no doubt that the DMU cars have distinct advantages for urban rail systems, partly because they are small and light. They’re sleek, modern-looking (more like today’s streetcars or light rail trains), smooth-riding and don’t make as much noise as trains like the Trinity Railway Express with their heavy locomotives.They’re more neighborhood-friendly. That will be important for TEX Rail, which will cross several neighborhoods in Fort Worth and Northeast Tarrant County.On the downside, they’re costly. The T would have to spend about $90 million for DMU cars on the TEX Rail, about $25 million more than TRE-style cars and locomotives.Transit officials say that the extra cost can be made up quickly from lower maintenance and fuel costs for the DMU cars.It’s crucial that TEX Rail meet its schedule and be opened to riders in 2017. That depends on many things, not the least of which is securing millions of dollars in federal funding.Addressing all safety-related concerns is an essential part of the process.Officials at the T can be taken at their word that they will make sure the shunting problem is thoroughly addressed. It will help if their selection process for TEX Rail cars is open and transparent, so potential riders will know not to worry.