ERTMS – philosophies with a driver supporting signalling system

The new European signalling system, ERTMS, will have a big impact on how the driver operates the train. ERTMS is in fact a signalling system that gives possibilities to support the driver in planning and driving of the train. This is a big difference for a lot of countries where the ATP-system of today is ‘punishing’ the driver.

In ATP-systems without driver support, the system acts as a ‘watch-guard’, meaning that as long as the driver keeps below a speed making it possible to stop in due time before a dangerous point, then the driver will be in control of braking the train and the signalling system will remain inactive. However, if the driver does not brake the train in the correct manner, some of the systems will alarm the driver that it is time to start braking the train. All systems do not alarm the driver though but rely on the driver knowing when to brake based on line side optical signal aspects or boards. For instance, if the driver is making a mistake and not braking the train sufficiently, the signalling system will intervene and the emergency brake will be activated to brake the train.

Emergency brakes for slowing down is undesirable

Is this not what we want?

Naturally, we want the train to stop to avoid an accident, but not all braking is performed to stop the train but instead to decrease speed before a bridge, a tunnel, a curve or something else. However, every emergency brake activation is undesirable. In some of the ATP-systems the brake intervention is revocable, meaning that when the speed drops below a sufficient level the emergency brake can be released and the driver can take control of the train again. In other systems, an activated emergency brake cannot be revoked meaning that a train is braked to stop every time. Even if the emergency brake is revocable there are still drawbacks. For pneumatic brake systems, an emergency brake means emptying the main brake pipe. It could take considerable time to build up the brake pressure in the valves again meaning that the train will more or less be braked to stop anyway. A consequence of emergency brake to stop is often flat wheels and long disturbance times. This is especially true for long freight trains. Emergency braking in passenger trains is also undesirable since passengers may fall and be injured. So braking a train with an emergency brake should be avoided in every possible way.

Driver behaviour

How do drivers behave using these systems?

Drivers simply drive the train at a lower speed than what is possible. They want to make sure that the train stays below the critical speed where the ATP would intervene with an emergency brake and ‘punish’ the driver. In some countries, there are even two drivers in the cabin to supervise each other making sure that the active driver does not miss alarms from the ATP-system. The conclusion is that these ATP-systems turn out to be more expensive due to more personnel and/or a lower performance.

Supporting systems with service brakes

Some of the existing ATP-systems, for example the Swedish ATP (Ebicab 700) and especially the new European signalling system ERTMS, are intended and designed to support the driver. This is achieved by adding a service brake to the existing emergency brake. A service brake is activated before the emergency brake is activated with a ‘softer’ brake which is also revocable. The emergency brake will never be applied unless there is a failure on the service brake.

In a driver supporting ATP-system (like ERTMS), the driver is alerted when approaching a point where the service brake will be activated (similar to the situation for emergency brake), but there is no big downside for the driver to ‘get caught’ by the service brake because it will brake almost as softly as most drivers do. The driver can always take the control back again below a certain speed.

High speed, critical performance criteria

For the driver this means that he can, and will in most cases, drive the train very near the maximum speed allowed without risking emergency intervention if he makes a mistake. This has turned out to be a very important issue for example in Sweden where we have long distances to cover with long and heavy freight trains. High-speed often becomes a critical performance criteria for freight trains.

An increase by 10km/h by philosophy

The differences in driver behaviour were observed recently in simulations performed by ERA in Munich in March 2008. It became evident that drivers used to drive with emergency brake intervention only drove in average at 10km/h lower speed than drivers used to service brake intervention.

Reduced drawbacks by feedback

The ‘supporting’ ATP-systems though have some drawbacks. The service brake is not considered safe and therefore it has to be activated before the emergency brake. The driver will have to brake somewhat earlier compared to a system with only emergency intervention. This of course has impediments on the performance. In Sweden, the drawbacks with service brake have been reduced by implementing feedback from driver activation of the brakes. When the driver activates the brake, the ATP-system ‘knows’ that the driver is ‘awake and ready’ and the time for ATP intervention of service brake can be delayed. For ERTMS, a solution for optimising the serviced brake for feedback is under development, making ERTMS a ’state-of the-art’ system – not only an excellent European ATP-system for high-speed trains – but also a very useful and high performing ATP-system for long freight trains.

ERTMS – a better environment for the driver

It is our belief that ERTMS is an excellent European ATP-system for high-speed trains, but will also be a very useful and high performing ATP-system for long freight trains that supports the driver instead of punishing him. The philosophy with a system that supports the driver increases the overall performance and thus competition for the railways.