The Denton County (Texas) Transportation Authority is operating a fleet of lightweight Stadler GTW 2/6 Multiple Rail Unit commuter vehicles on its A-train line following a waiver earlier this summer from the Federal Rail Administration. © Urban Engineers
A commuter line in Texas receives an FRA waiver to operate lightweight cars in a corridor shared by traditional Federal Rail Administration-compliant vehicles.
September 4, 2012—Earlier this summer, the Denton County (Texas) Transportation Authority (DCTA) received a waiver from the Federal Rail Administration (FRA) to operate lightweight Stadler GTW 2/6 Multiple Rail Unit low-floor commuter vehicles on corridors shared by more traditional FRA-compliant vehicles within its A-train commuter line. This is the first waiver granted by the FRA since its Rail Safety Advisory Committee (RSAC) prepared guidelines in 2009 for evaluating alternative designs.
“We worked closely with the FRA and RSAC to develop the criteria,” said Dee Leggett, the vice president of program development for DCTA in written comments to Civil Engineering online. “Once the criteria were finalized, we made minor modifications to the vehicle to comply with the new criteria. The bulk of the effort was working with the FRA and Stadler to demonstrate compliance through performance testing and computer modeling.”
Modifications to the vehicles focused on fuel tank design, seat design, and the emergency escape window, Leggett said. Stadler engineers worked with the John A. Volpe National Transportation Systems Center, in Cambridge, Massachusetts, designing and running computer simulations of crash scenarios to prove the effectiveness of the vehicle’s crash energy management system.
The waiver enables the DCTA to integrate 11 new diesel-electric GTW 2/6 articulated rail cars with compliant Budd Rail Diesel Cars (RDC) leased from Dallas Area Rapid Transit (DART) for the system’s opening in June 2011. The articulated, modular GTW cars have a central power core designed for straightforward access to maintenance items, reducing time out of service. The ADA-compliant vehicles seat 104 and are capable of traveling at 75 mph.
The A-train shares corridors with the Dallas Garland & Northeastern Railroad (DNGO), but the freight trains and commuter trains are separated temporally, and DCTA doesn’t anticipate mixing the two. The waiver provides flexibility for future expansions, however, on shared corridors in which temporal separation is not possible, Leggett said.
Denton County is one of the fastest-growing counties in the United States; the population increased 52.1 percent between April 2000 and July 2009, according to the U.S. Census Bureau. Between 2010 and 2011, the county of more than 686,000 added 23,792 residents, according to the U.S. Census Bureau.
“Denton County was facing tremendous population growth,” Leggett said. “The county has three major higher education institutions with 60 percent commuters. At the same time, DART was expanding its light-rail line north, close to the Denton County line. Area leaders saw an opportunity and a need to form a transit agency with its primary purpose being the development, construction, and operation of a commuter rail line.”
The 21 mi long line connects to the DART system in the city of Carrollton, providing commuters with an alternative to Interstate 35, a primary NAFTA corridor that is about to undergo construction.
Construction began on the line in 2009, Herzog Contracting of St. Joseph, Missouri, and Archer Western of Atlanta serving as contractors. A partnership of Urban Engineers, of Philadelphia, LAN of Houston, and Bowman Engineering/Consulting, of Dallas, provided design services and construction management.
“At the beginning of the project we came up with nearly $30 million in value-engineering ideas to get construction costs within budget,” says Bradley Davis, P.E., who was a construction manager for Urban Engineers during the project. Davis says the DCTA was able to reuse a DGNO corridor which is owned by DART. Upgrading the existing infrastructure proved to be more cost effective than building a new corridor and eliminated the need for several bridges. The team also found cost savings in the line’s five canopied platform stations, specifying foundation changes that quickened construction.
The project included a 56,000 sq ft operations and maintenance facility, which provided an engineering challenge. Because the $19-million facility is sited on an unregulated dump, engineers needed to devise a structural solution for the building’s foundation and design a vapor barrier and methane detection system.
“During excavation, there were challenges not knowing what types of materials we were going to encounter. We didn’t encounter any material that was hot or asbestos; it was mostly old construction material,” Davis says. “We had a very high water table. A point well system had to be set up around the site to get the water down to a point where we could construct the foundations of the facility.”
“We excavated out over 10 feet of the landfill material, then backfilled and compacted with select fill. We drilled piers, and then poured grade beams and the foundation on top of that.”
The system cost $350 million, which includes the cost of vehicles. It accommodates about 1,500 riders a day, with the capacity for 8,000, which is the ridership DCTA research projects in about 25 years.