Are Trains Pulled or Pushed to Their Destination?
When considering the transport of long trains over distances, a natural question arises: Are train lines ever pushed over distances to their destination by the locomotive, or are they only ever pulled? This article explores the mechanics behind train movements and the reasons why pulling is the standard practice.
Why Trains Are Pulled Rather Than Pushed
The primary reason for pulling trains rather than pushing them is the design and mechanics of trains. The following points highlight the advantages of using a locomotive to pull instead of push.
Coupling Mechanics
Trains are designed with couplers that connect cars in a way that is most effective for pulling. The coupling mechanism is generally stronger in tension than in compression. This makes it safer and more efficient to pull a train, ensuring stability and reducing the risk of derailment.
Locomotive Design
Locomotives are engineered to pull rather than push, particularly for long-distance travel. They are equipped with powerful traction systems that allow them to pull heavy loads. The weight distribution in locomotives also enhances stability while pulling.
Pulling provides better control over the train's movement, especially in terms of braking and acceleration. When a train is pulled, the weight of the cars helps stabilize the train, reducing the risk of derailment. By comparison, pushing a train can be riskier, as the locomotive can become unstable and potentially derail.
Scenarios Where Locomotives Push Trains
While pulling is the standard practice, there are certain scenarios where locomotives push cars, such as in yard operations or when maneuvering in tight spaces. However, these scenarios are less common for long-distance travel due to the associated risks and challenges.
Introduction of Push-Pull Trains
Despite the challenges, numerous countries now operate push-pull trains, which resemble passenger trains with the locomotive on one end and a cab car on the other. This design allows the locomotive to be operated remotely from the cab car, eliminating the need for a driver to sit in the locomotive.
This concept was initially introduced for short regional trains that frequently changed direction and operated in the 1990s. Countries such as Germany, Switzerland, France, and Great Britain have since adopted this method for intercity trains. In Austria, Railjets operate as push-pull trains, both locally and internationally.
Features of Cab Cars
A cab car in a push-pull train is equipped with all the necessary signaling systems for the line and has two-way communication with the locomotive. This ensures that the driver can monitor the train's performance and address any issues promptly. Additionally, cab cars transmit real-time diagnostic data to the driver.
Challenges of Pushing Trains
While push-pull trains offer various advantages, they also present unique challenges. A relatively lightweight cab car might derail more easily if it encounters obstacles such as snow drifts, fallen trees, or vehicles on level crossings. The risk is higher when the train is standing still, as the driver may not notice when wheels are rotating, leading to possible failures in acceleration on steep grades during winter.
Pushing forces transmitted by buffers/couplings must be carefully considered, especially in curves. High-speed trains also face concerns about derailments caused by side winds, which must be addressed in the design of cab cars.
Conclusion
While locomotives can push trains under certain conditions, they are predominantly used to pull them due to safety, stability, and efficiency. Despite the challenges, the use of push-pull trains is becoming more common in both local/commuter and intercity operations. Even the new nightjet overnight trains in Austria are designed as push-pull trains, although this method is less common in freight operations.