Western Rail Coalition > The Trains > Locomotive Haulage Vs Multiple Units
Locomotive hauled or multiple unit trains?
There are two primary types of passenger trains, locomotive-hauled (LH) and multiple-unit (MU).
Locomotive Hauled Trains
Locomotive-hauled (LH) trains feature a separate locomotive pulling unpowered passenger cars. Regional / commuter rail operations in the U.S. have traditionally used this type of train with anything from 2 to 12 cars. Locomotives by their very nature are ‘dead’ space on the train as they carry no fare-paying passengers and add a fixed length and weight to the consist, regardless of the number of cars being hauled. Generally locomotives are an efficient source of power for trains that have at least 8 cars, however they represent an increasing penalty in weight and therefore acceleration performance and energy consumption for shorter consists.
That said, locomotive hauled trains offer operational flexibility as individual cars and locomotives can be swapped independently in and out of consists in response to operational and maintenance requirements.
A typical regional / commuter rail locomotive hauled consist features a 4-axle locomotive, a number of regular passenger cars and a cab-car at the other end. This type of operation, also know as “push-pull”, allows the train to be operated from both ends and avoids the need for shunting or reforming the consist at the ends of the line.
Both new and used locomotives and hauled passenger cars are widely available in the U.S. including those that meet the Environmental Protection Agency’s Tier 4 requirements, which limit the amount of particulate matter (PM), or black soot, and nitrogen oxides (NOx) that can be emitted from the diesel engine.
Multiple Unit Trains
Self-propelled multiple unit trains (MUs) feature a number of cars coupled in a semi-permanent consist with the power and propulsion systems distributed throughout the train. Equipment is usually located underneath the the cars, in closets throughout the train and / or on the roof. An operator’s cab is provided at both ends so the train can be driven in both directions. Multiple unit trains can be specified with powered or unpowered intermediate cars to provide the optimal train length required which also means the amount of motors provided to move the train forward can be scaled appropriately.
The abbreviation ‘MU’ is often prefixed with a letter that identifies the train’s power source, for example ‘DMU’ stands for diesel multiple unit, ‘EMU’ means Electrical Multiple Unit and ‘BEMU’ signifies a battery electrical multiple unit. ‘Bi-mode’ or even ‘tri-mode’ trains are available which offer effortless switching between power sources, usually at speed. The ‘multiple’ in the title indicates the ability to quickly couple two or more units together to provide a longer train.
Multiple units are generally lighter, faster, and require less platform space than locomotive-hauled trains. Electric motors distributed throughout the train (rather than being consolidated under a single locomotive) offer advantages in the amount of propulsion provided can be increased according to the number of cars on the train. Acceleration is fast, smooth, and just like an ‘all-wheel drive’ road vehicle, adhesion on steep gradients in bad weather is improved. However multiple units have more limited availability in the U.S. They can also be more complex to service as typically the consist must be taken out of operation as a complete set when major issues arise.
Rolling Stock Comparison
| Train | Locomotive Hauled MotivePower MP36PH Bombardier Bi-Level Cars | Multiple Unit Stadler FLIRT 3-car Bi-Mode DMU / EMU. | |
| Configuration | Locomotive + 2 Cars | 3-car Multiple Unit | |
| Length | 238 ft | 213 ft | |
| Power | 3,600 hp | 1,400 hp (diesel mode) | |
| Weight | 553,000 lbs | 308,000 lbs | |
| Power / Weight Ratio | – | – | |
| Maximum Speed | 100 mph | 100 mph | |
| Acceleration | – | 2.3 ft/s^2 (diesel mode) | |
| Fuel Consumption | X | ||
| Availability in the U.S. | X | ||
| Reconfigurability / Speed of Repair | X | ||
| Platform Space Efficiency | X | ||
| Track Wear & Tear | X |
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