By Kevin Wilcox
DART deploys an innovative, dual-mode streetcar system that crosses a historical bridge to connect trendy neighborhoods to downtown.
A new dual-mode streetcar uses battery power to cross the Trinity River via the Houston Street Viaduct, an open-spandrel arch bridge listed in the National Register of Historic Places. © Mike Cameron, HDR
March 15, 2016—When city leaders in Dallas began considering ways to better connect the downtown area such neighborhoods to the southwest as North Oak Cliff and the trendy and eclectic Bishop Arts District, a modern streetcar system quickly rose to the top of the options list. Such systems have light, nimble vehicles that blend seamlessly into the urban and community fabric and can be very reliable.
They also have a key intangible. "There is something about rail that people flock to," says Timothy H. McKay, P.E., M.ASCE, the executive vice president of growth and regional development for Dallas Area Rapid Transit (DART). DART is developing and operating the system, which is owned by the City of Dallas and was financed with a U.S. Department of Transportation TIGER (Transportation Investment Generating Economic Recovery) grant to the North Texas Council of Governments. The first phase of the project opened in April 2015. A second phase is under construction, scheduled for completion later this year.
"At the end of the day, I think…people just have an infatuation with rail, frankly," says McKay, who notes the streetcar is undergoing a bit if a renaissance; street car service has been instituted or reinstituted in such cities as Seattle, Salt Lake City, Atlanta, and Washington, D.C., over the past 10 years. "It's coming back to where we were here in Dallas about 60 to 65 years ago," he says.
This resurgence has driven real estate investment in the areas around stations, which are typically clustered more tightly than on a light-rail system and are more permanent—and prominent—than bus stops. "When you have rail in the ground, developers will invest money because they know that route is not going to change," McKay explains.
When completed, the Dallas system will operate on 1.6 mi of embedded track; approximately 1 mi of that will be on a dedicated bidirectional streetcar lane. The line begins at Union Station to provide connections with commuter rail, light-rail, and city bus systems. There are currently two stops before reaching the termination point at Methodist Dallas Medical Center; the second phase will add two additional stops.
One of the key engineering and design challenges of the first phase of the project was how to cross over the Trinity River via the Houston Street Viaduct, an open-spandrel arch bridge completed in 1911. The 4,785.3 ft long concrete span is listed in the National Register of Historic Places, which means modifications had to be kept to a minimum. The design/build team for the first phase was Stacy and Witbeck/CARCON Industries (SWC), a joint venture of Stacy and Witbeck, Inc., of Alameda, California, and CARCON Industries, of Dallas, working in association with HDR, Inc., Omaha. Engineering consultation was provided by TRACK3, a joint venture of Lockwood, Andrews & Newnam, Inc. (LAN), of Houston, and three Dallas firms: APM & Associates, Inc., Aguirre Roden, Inc., and CP&Y.
"We went through…a pretty extensive investigation process, inspecting the entire structure to determine how much deterioration had taken place over those 100 plus years," says Josh LaFleur, a project manager at Stacy and Witbeck. "Surprisingly, the bridge was in better shape than we expected. Originally we had anticipated that we were going to remove the entire deck slab. Instead, the team was able to maintain the deck and develop a series of concrete patches to the bridge's arches."
Another factor that kept bridge renovations to a minimum was the use of an innovative new type of block rail that is just 3 in. tall, compared to the nearly 7 in. of a typical T rail, says Luke Olson, P.E., a professional associate at HDR. "We were able to eliminate about 4 inches of concrete thickness," he says. "Four inches of additional concrete for the width of a traffic lane would be a lot of additional load and could've put us into some additional strengthening needs."
The system uses an innovative, dual-mode streetcar developed by Brookville Equipment Corporation, headquartered in Brookville, Pennsylvania. The cars are equipped with a retractable pantograph to draw power from an overhead catenary system and lithium ion battery packs, as well. McKay explains that stringing catenary wire across the historical bridge presented difficult logistics and aesthetics challenges. "Because we had a timeline on the grant, we thought it was probably easier and quicker to develop a vehicle that was dual-mode," he explains.
Sofia Ojeda, P.E., M.ASCE, an associate of LAN, explains how the dual-mode process will function on a typical trip. "At the Union Station stop…the pantograph lowers to disconnect from the overhead catenary system in preparation for the journey south across the Houston Street Viaduct crossing the Trinity River," she says. "Once lowered, the streetcar travels southbound, using battery power, over the Houston Street Viaduct to the next stop at Greenbriar Lane and Zang Boulevard. Once there, the pantograph will raise and connect back to the catenary system."
The dual-mode capability means that the cars can operate for approximately 7 mi in the event of an electrical or catenary system failure, enabling them to return to their maintenance yard. The batteries, which will typically carry a 60 percent charge, are recharged through the catenary system.
Because the team didn't need to replace the robust bridge slab, they had funds available to add such amenities to the streetcar stations as canopies, lighting, benches, and trash receptacles, says LaFleur. "As part of the community engagement aspect of the project, SW/C created a canopy design competition open to local high school students. Along with a scholarship, the two winners were given an internship to work with the designers, product suppliers, canopy manufacturers, and SW/C in the selection and installation of the canopy materials and station amenities."
The first phase of the system, which operates daily from 9:30 a.m. to midnight, is popular with city residents and tourists alike. Additional expansions are in the planning stages, including a 3.5 mi crosstown route that would connect with the McKinney Avenue Trolley, a vintage streetcar system.
"Once the system is complete it really gives people choices," McKay says.