A Stadler FLIRT DMU, painted in DART Silver Line colors at rest on the Salt Lake, Garfield & Western Railway.
(Xboxtravis7992, CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons)
DIESEL MULTIPLE UNIT (DMU)
A diesel multiple unit or DMU is a multiple-unit train powered by on-board diesel engines. A DMU requires no separate locomotive, as the engines are incorporated into one or more of the carriages. Diesel-powered single-unit railcars are also generally classed as DMUs. Diesel-powered units may be further classified by their transmission type: diesel–mechanical DMMU, diesel–hydraulic DHMU, or diesel–electric DEMU.
Design
The diesel engine may be located above the frame in an engine bay or under the floor. Driving controls can be at both ends, on one end, or in a separate car.
Types by transmission
DMUs are usually classified by the method of transmitting motive power to their wheels.
Diesel–mechanical
In a diesel–mechanical multiple unit (DMMU), the rotating energy of the engine is transmitted via a gearbox and driveshaft directly to the wheels of the train, like a car. The transmissions can be shifted manually by the driver, as in the great majority of first-generation British Rail DMUs, but in most applications, gears are changed automatically.
Diesel–hydraulic
One of the underfloor diesel engines with hydraulic transmission under a car of JR Shikoku 2700 series DMU
In a diesel–hydraulic multiple unit (DHMU), a hydraulic torque converter, a type of fluid coupling, acts as the transmission medium for the motive power of the diesel engine to turn the wheels. Some units feature a hybrid mix of hydraulic and mechanical transmissions, usually reverting to the latter at higher operating speeds as this decreases engine RPM and noise.
Diesel–electric
"Power Pack" car of Stadler FLIRT DMU with open bay of a diesel-generator. The Jacobs bogies under this car do not have their own traction motors, which are mounted on bogies under other cars.
In a diesel–electric multiple unit (DEMU), a diesel engine drives an electrical generator or an alternator which produces electrical energy. The generated current is then fed to electric traction motors on the wheels or bogies in the same way as a conventional diesel–electric locomotive.
On some DEMUs, such as the Bombardier Voyager, each car is entirely self-contained and has its own engine, generator and electric motors. In other designs, such as the British Rail Class 207 or the Stadler GTW and Stadler FLIRT DMU, some cars within the consist may be entirely unpowered or only feature electric motors, obtaining electric current from other cars in the consist which have a generator and engine.
With diesel–electric transmission, some DMU can be no other than an EMU without pantograph or contact shoes (for use on the former British Rail Southern Region), which "is substituted" by one or more on-board diesel generators; this kind of DEMU can be potentially upgraded to electro-diesel multiple unit (EDMU), becoming a bi-mode multiple units train (BMU), just adding one or two pantographs or contact shoes (with opportune converters, if necessary) and related modifications on the electric system.
Two Bombardier Talent low-floor DMUs on the O-Train Trillium Line in Ottawa, Canada.
(Earl Andrew, CC0 Public domain, via Wikimedia Commons)
Use in North America
Canada
Canada generally follows similar buffer strength requirements to the US, but new services are evaluated on a case-by-case basis. As a result, several types of lightweight DMUs have been used:
The O-Train Trillium Line in Ottawa, Ontario uses European-standard Alstom Coradia LINT (previously Bombardier Talent) DMUs on conventional railway tracks under a specific safety agreement with Transport Canada.
Via Rail operates Budd Rail Diesel Cars on its Sudbury – White River train.
Réseau Charlevoix (Le Massif) operates a shuttle in the Charlevoix region, Québec, using ex-Deutsche Bahn DB Class 628 units.
Canadian National operates the small custom-built Kaoham Shuttle between Lillooet, and D'Arcy via Seton Portage, 213 km (132 mi) northeast of Vancouver, in a partnership with the Seton Lake Indian Band.
Union Pearson Express uses Nippon Sharyo DMU trains for express service between Union Station and Pearson Airport.
Apollo 2400 DMU in service in Costa Rica.
(Haakon S. Krohn, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons)
Costa Rica
Costa Rica has purchased several Apolo 2400 series DMU railcars from the former narrow gauge operator in Spain, which are run in commuter service.
Mexico
42 X'Trapolis Tsíimin K'áak train sets have been ordered for Tren Maya, 10 of which are DMU and 32 are EDMU.
Budd Rail Diesel Car RDC-1 No. 407 of the Cape May Seashore Lines, New Jersey.
(Bevis R. W. King, CC BY-SA 3.0 <http://creativecommons.org/licenses/by-sa/3.0/>, via Wikimedia Commons)
United States
A type of diesel multiple units in the U.S. was the Budd Rail Diesel Car (RDC). The RDC was a single passenger car with two diesel engines and two sets of controls.
In the United States, DMU systems must be FRA-compliant to be permitted on freight rail corridors. The Federal Railway Administration has mandated higher coupling strength requirements than European regulators, effectively prohibiting the use of lighter weight European-style inter-city rail DMUs on U.S. main line railways without timesharing with freight operations or special waivers from the FRA. This has greatly restricted the development of DMUs within the U.S. as no other country requires the much heavier FRA compliant vehicles, and no export market for them exists.
FRA compliant Colorado Railcar DMU of WES Commuter Rail.
(TriMet, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons)
Operations using FRA-compliant vehicles:
- Since February 2009, TriMet is using FRA-compliant Colorado Railcar DMUs for its rush-hour WES Commuter Rail service, a suburb-to-suburb line between Beaverton and Wilsonville, Oregon. The opening of the line was delayed from fall 2008 to early 2009 due to delays in getting the vehicles. TriMet also has four refurbished former Alaska RR and Trinity Railway Express RDCs as backup trainsets for when one or more Colorado Railcar DMUs is out of service.
- Sonoma–Marin Area Rail Transit, also referred to as SMART, operates Nippon Sharyo DMUs (the same as those in Toronto) on its route between Larkspur and Santa Rosa, California. Service commenced in 2017.
Operations using non FRA-compliant vehicles:
- Capital Metro uses Stadler GTW cars to operate Capital MetroRail, a commuter rail line serving the Greater Austin, Texas area.
- In Denton County, Texas, DCTA also uses Stadler GTW cars to operate its A-train service. DCTA has secured from the FRA the first-ever alternative vehicle technology waiver to use these cars on active freight corridors.
Stadler FLIRT owned by TEXRail in Texas.
(Danazar, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons)
Operations using non FRA-compliant vehicles (cont.):
- TEXRail in Tarrant County, Texas is a commuter rail line operated by Trinity Metro which uses Stadler FLIRT DMUs. The vehicles are FRA Alternate Compliant. The line has 9 stops with termini at DFW Airport and T&P Station.
- NJ Transit operates the River Line from Camden, NJ to Trenton, NJ, every 15 minutes during peak hours and every 30 minutes at other times. It uses modified Stadler GTW trains of one or two cars. The line is classified as light rail because it utilizes imported European made DMUs that do not meet FRA crash guidelines. The cars may not operate with the freight rail service that shares the line, so evening operating hours are restricted to Saturday nights. This line currently carries over 7,500 passengers on a typical weekday, exceeding expectations.
- NCTD operates the Sprinter line using Desiro Classic DMUs built by Siemens. Opened March 2008, The line operates every half-hour daily, except limitations in the morning and at night on Saturday, Sunday and on holidays. The line runs from Oceanside, CA, where transfer is possible with Coaster commuter rail service to San Diego, to Escondido, CA. Like the NJT River Line, it is classified as light rail due to the use of European made DMUs, but does not run at a more typical light rail frequency.
- The eBART expansion of the Bay Area Rapid Transit system implements Stadler GTW diesel multiple unit train service from Pittsburg/Bay Point station east along the Highway 4 corridor to the town of Antioch. Future expansions in this direction could also connect the eBART service to Oakley, Brentwood, Byron, and beyond to Tracy and Stockton. The DMU system was chosen as a less-expensive alternative to the existing third-rail BART design. Service began on 25 May 2018.
- Arrow utilizes Stadler FLIRT trainsets along its service route in Redlands, California.
Proposed operations:
- The Los Angeles County Metropolitan Transportation Authority approved an allocation of $250,000 for a feasibility study of DMUs for "future transportation options for the region" on 5 July 2006 (Ara Najarian, Metro Board Member).
- Chicago's commuter rail line, Metra, is studying the use of DMUs on its newly proposed lines (STAR line, SES). They claim these DMUs will have better acceleration, be more fuel efficient, and seat more customers than the current diesel locomotive and double decker rail cars that are currently in use.
- Seattle area – The Central Puget Sound's regional transit agency Sound Transit, along with the Puget Sound Regional Council evaluated the feasibility of both DMU and diesel locomotive technology for operation in the Eastside BNSF Corridor in response to a state legislative request. The Eastside BNSF corridor runs from the City of Snohomish in the north to Renton in the south of the metro area. Sound Transit has no plans to operate passenger rail service in the eastside BNSF corridor, but has committed limited funds to provide capital improvements in the event another public or private operator proposes to operate the service.
- Anchorage Mat-Su area – As part of a joint U.S. Forest Service (USFS) and ARRC Chugach Forest Whistle Stop project, a self-propelled rail car was purchased and delivered spring 2009. The diesel multiple unit (DMU) may be available for flexible demonstration service during winter months.
- The Long Island Rail Road, the busiest commuter railroad in the United States, is exploring the possibility of operating DMUs on some of its lesser traveled routes in non-electrified territory (on the Montauk, Greenport, Port Jefferson, and Oyster Bay branches), where operation of its current fleet of C3 bilevel railcars pulled by DE30AC/DM30AC locomotives is uneconomical and inefficient.
- A proposal to use DMUs on Boston's Fairmount Line was initially approved, but was canceled in 2016.
- NJ Transit's Passaic–Bergen–Hudson Transit Project is studying the re-introduction passenger service on a portion of the New York, Susquehanna and Western Railway (NYSW) right-of-way in Passiac, Bergen and Hudson counties using newly built, FRA-compliant diesel multiple units.
- Dallas Area Rapid Transit is rebuilding the Cotton Belt Rail Line as the Silver Line, which will utilize Stadler FLIRT units.
