A Eurostar from Paris to Amsterdam travels through 3 different countries, and with today’s technology it needs 4 different—incompatible—onboard systems to read signals and manage braking. These systems range from electromechanical to electronic to digital, and because they’re connected to the brakes and other key components, they’re essential for safety.

Historically, each European country developed its own signalling system or systems, tailored to its own needs, culture and technology. As a result, we now have 35 different signalling systems in Europe.

To create a single rail network, we need to create a single signalling system that works for every train that runs on it. That’s what the ERTMS effort is designed to do.

When you drive your car, you’re solely responsible for stopping on time, based on available information, such as signs, traffic lights, and the tail lights of vehicles ahead. But in the rail system, a train driver is supervised and supported. Their speed is monitored at all times: if it exceeds the established limit, an alarm will sound, and the brakes will be applied automatically by the signalling system now in place.

The European Union launched the ERTMS effort to unify the signalling and safety systems of its member countries. Its goals include:

• reducing unit costs for acquiring signalling equipment
• avoiding the costs of developing a different system for each country
• reducing barriers to entry for new operators
• paving the way for railway interoperability across Europe

How does ERTMS work?

Any signalling system requires information-sharing between the train and the line. It’s a bit like a red light for the driver of a car, or the roadside radar that reads the speed of your vehicle.

In Level 1 ERTMS, train drivers get information and instructions delivered directly to their cabs, thanks to real-time data from lineside transponders that relay signal status.

And in Level 2?

In Level 2 ERTMS, the same information is exchanged by radio, using the GSMR system, which transmits data between the train and the local radio block centre (RBC), a computer that manages traffic in a specific area. The train continuously reports its position by radio. For example, it notifies the RBC that it passed a transponder marking a specific location at time T, and specifies the number of wheel rotations since that transponder.

How is this data used?

Because the wheels have a known diameter, these data points can be combined to calculate the train’s position exactly. In response, the lineside equipment radios the train that it’s authorized to run at X speed for Y km, or that it needs to slow down to Z km per hour starting from a certain distance. All of this is calculated based on the exchange of information.

How does this affect the driver?

With Level 2 ERTMS, driving a train is more like driving a car. When you’re at the wheel and you see a red light in the distance, you often let your car coast in the hope that the light will change to green and you won’t have to stop. But you can increase your speed as soon as the light turns green. Driving a train is different. Before the red light, you always have a yellow light telling you to slow down, and the system controls your slower speed. But with Level 2 ERTMS, drivers can anticipate their next move. It’s much more fluid.

Can you run more trains?

Yes—provided the traffic is homogeneous. If all the trains are moving at the same average commercial speed, Level 2 ERTMS lets them run closer together. With less headway required between trains, you can put more of them on the same track.

Can you reduce traffic back-ups?

That’s what will happen on the Paris-Lyon corridor. With Level 2 ERTMS, it will handle 20% more trains—without building additional track. But that doesn’t work if different trains are running at different speeds. By definition, a direct train moves faster than a local. The faster train will inevitably catch up to the slower one and have to wait behind it, just as motorists have to slow down behind a truck on the motorway—except that a car can pass a truck.

With Level 3, we’ll have a ‘moving block’ system. Headway between trains will depend not only on the geography of the line, but also on the trains’ relative speeds. It’s similar to what all of us do when we drive a car. The distance between vehicles isn’t the same in the city as on the motorway.

At Level 3 ERTMS, we can phase out fixed blocks. What does that mean? In the railway industry, a ‘fixed block’ is an inflexible, indivisible length of track—essentially the unit of account for railway lines. Today, a fixed block is 1,500 m long in France. That’s the distance we need to be sure that even the heaviest train can stop.

No train can enter a 1,500-m segment of line if another train is already in it. But with Level 3 ERTMS, we can know exactly where a train is on a line. We can let the train behind it into the first stretch of that 1,500-m segment—provided we know the second train’s braking capacity and we’re sure it can be stopped before it causes a collision. 

When we know not only where a train is and how long it is, but where the end of the train ahead of it is, we can reduce the distance between them.

Knowing the exact distance between any two trains in real time lets us increase capacity, save time and make traffic smoother. Bottom line: Level 3 ERTMS is critical in responding to growing demand for mobility, because it lets us run more trains on the same track.

The European Union has set a timeline for deployment of ERTMS, starting on the lines with the heaviest traffic, and ending on lines with average traffic. In all, that’s about 100,000 km of line across Europe—including 17,000 in France—by 2040 or 2050.

ERTMS technology must be installed on both line and rolling stock, which requires a great deal of coordination. In general, EU member countries plan to have only one system at a time on their lines, which means that trains will temporarily have 2. The aim is to have all trains upgraded by the time the legacy track system is replaced by ERTMS.

Trains are now being equipped with the new technology in advance. This is true for the Cannes-Ventimiglia line, which will soon have hybrid Level 3 ERTMS¹. The big night will arrive sometime in 2026 or 2027: for the first time, we’ll turn off the signals on a legacy line in France.

In 2007, the Est Européen high-speed service between Paris and Strasbourg became the first line in France to be outfitted with Level 2 ERTMS, though commercial use of the new system didn’t really begin until 2013-2014.

Installing ERTMS on the Tours-Bordeaux and Le Mans-Rennes high-speed lines—both inaugurated in 2017—was crucial because it was the only way to cut travel time between Paris and Bordeaux to 2 hours. To meet that goal, trains must run at 320 km/h between Tours and Bordeaux, up from 300 km/h between Paris and Tours.

The theory is that ERTMS will boost revenue and cut costs for rail operators. Revenue should rise because more trains can run at the same time, and because harmonizing European rail traffic will eliminate technical ‘borders’, making it easier for travellers to choose rail. Costs should fall because ERTMS opens the door to a single market for rail ‘products’. Instead of serving 27 different national markets, manufacturers will have access to a single European market, which should allow for lower unit production costs.

It will take a long time for ERTMS investments to pay off, and rail operators must follow strict rules for sound financial management. That makes it harder for them to make funds available for the transition. European subsidy programmes are working to make operators more willing to commit by helping offset the long horizon for return on investment. The subsidies offer 10%—and in special cases even 30%—funding, and that can help close the deal on deploying ERTMS.