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Operational Testing of Stadler FLIRT DMU Trainsets

Written by Matt DeGeorge, Senior Railway Research Engineer, ENSCO Inc.; and Lucy Andre, Chief of Staff, Stadler US Inc.
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TTC Operated by ENSCO photo

TTC OPERATED BY ENSCO, RAILWAY AGE FEBRUARY 2023 ISSUE: Stadler US Inc. has begun operational testing of its low-floor FLIRT Diesel Multiple-Unit (DMU) trainsets for Dallas Area Rapid Transit (DART) at the Federal Railroad Administration’s Transportation Technology Center (TTC) in Pueblo, Colo.

The TTC has long been used as the ideal location for testing new passenger rolling stock ahead of delivery to the transit operator because in-depth vehicle qualification testing occurs in a controlled environment separate from revenue service, before the vehicles are delivered. Proper attention to detail can be applied without interfering with transit operations to ensure maximum safety and reliability. This is a key benefit to the industry.

The Stadler FLIRT DMU for DART is the first passenger trainset being tested at the revitalized TTC since ENSCO assumed operational responsibilities in October 2022, having won a competitive bid and contracted to operate and expand the breadth of transportation modalities that can be tested on-site. Stadler arrived with two FLIRT DMU trainsets. The first unit is being used for qualification testing, while the second is being stored until delivery to DART. Additionally, the trainsets were featured in the TTC 50th Anniversary Event on Oct. 25, 2022, during which attendees enjoyed a historic ride on the DMU around the TTC’s largest test loop, symbolizing the beginning of a new era for the TTC.

Trainset Background

The DART contract for eight FLIRT trainsets was awarded to Stadler in June 2019. Train operation will occur on the commuter route between the northern railway terminus at Dallas/Fort Worth International Airport and Plano. Each DMU is comprised of four passenger-carrying units, two on each side of a separate midsection power unit housing a power pack consisting of a diesel engine and traction alternator (generator).

An important design feature of the Stadler FLIRT is that it can be designed to use different power sources such as batteries or hydrogen fuel cells. DART’s configuration utilizes four powered and eight unpowered axles. The trainset has the unique feature of quiet passenger compartments and a large amount of low-floor area because the power pack is installed in a separate midsection. This feature also isolates passengers from experiencing elevated vibrations. Total trainset length is approximately 266 feet, with capacity for 263 passengers (222 seated, 41 standing). Maximum operating speed is 79 mph.

Qualification Testing

The Stadler FLIRT DMU test program is separated into three phases that take place at different locations. Phase 1 consists of static and low speed testing at the Stadler facility in Salt Lake City, Utah. Phase 2 consists of static and dynamic testing at the TTC operated by ENSCO. This includes brake and traction performance, noise, EMC (Electromagnetic Compatibility) and onboard train control equipment testing. Phase 3 consists of final revenue track testing at DART prior to public revenue operation.

Due to its unique characteristics, the TTC is an ideal testing location for all new passenger rolling stock. The 52-square-mile facility contains 50 miles of test track that includes the Rail Transit Track (RTT), a 13.5-mile high-speed loop with a maximum speed of 165 mph and equipped with AC catenary; and the 9.1-mile Transit Test Track (TTT) loop with a maximum speed of 90 mph and equipped with third rail and DC catenary. Multiple tracks allow for continuous trainsets testing and simultaneous testing for other customers.

During the duration of the testing program at the TTC, the Stadler DMU and Stadler staff are home based in the Passenger-rail Services Building (PSB), a three-bay, 46,000-square-foot depot designed specifically for support of passenger car testing. The trainset and team are also supported with TTC staff and equipment to handle vehicle maintenance activities during testing, including installation and removal of bogies and other heavy components, machine shop for as-needed fabrication, and heavy machinery for loading and unloading ballast into the DMU to simulate passengers. Additionally, dedicated TTC onsite operation crews and subject matter experts help to ensure that testing operations stay within schedule and to assist in resolving any problems that may occur.

Brake and traction performance tests are done on the TTC high-speed test tracks to ensure that the DMU meets essential operational performance and safety requirements. This is key to perform at the TTC as opposed to on a transit’s revenue tracks so that revenue service is not impacted and Stadler has free control to make the test runs needed and allow time for adjustments to the vehicle. Similarly, noise testing is performed on the high-speed test tracks to confirm that the noise inside and outside the vehicle meets expectations to ensure comfortable experiences for passengers and the public.

EMC testing ensures that the DMU does not emit at-risk electromagnetic signals that could interfere with electronic infrastructure equipment and ensuring the DMU itself is not susceptible to anticipated outside electromagnetic interference. This is particularly important for the DMU’s train control system to ensure that it operates in anticipated electromagnetic conditions without issue. Finally, the train control system itself of the DMU is verified to be working as expected prior to delivery to the customer site.


The TTC Operated by ENSCO is aiding Stadler US to complete qualification testing at the TTC without interfering with DART’s revenue operations and helping to meet the mission of ensuring safe and reliable DMU operation. This testing marks the beginning of a long future for the TTC to serve the passenger rail industry.

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