Scientists believe "crash boxes" could save the lives of bus drivers

The effort to make everyday life safer for bus drivers may have taken a step in the right direction. In a new report from the Institute of Transport Economics, researchers show new testing methods and a specific design measure – a “crash box” – that can significantly reduce the risk of life-threatening injuries.

The report is written by Tor-Olav Nævestad and Manuel Laso. The former is a researcher at the Institute of Transport Economics and has worked with safety in bus transport, including collision safety, for a long time. Manuel Laso is a project manager at an international company that specializes in vehicle design and testing. The company operates what is considered by many to be Europe's best test track, but also offers digital simulation – a technique that allows you to test ideas at an early stage – before the car, bus or truck is built. In the work on the report, it is the latter technique, digital simulation, that is used to analyze the bus collision.

– We have seen in previous studies that collision safety for bus drivers is insufficient. And that was also something we already knew from the accidents we have had, says Tor-Olav Nævestad.

The previous studies concluded that there was a need to look more closely at possible reinforcements that could increase the safety of bus drivers. There is still no global standard for frontal crash protection for buses, and in Norway only the standard known as R-29 applies.

– When vehicles are tested to see if they meet R-29, a rectangular steel impactor is swung like a pendulum into the front wall of the cab, approximately at the level just below the windshield. But what we know, from three fatal bus collisions in Norway, is that this is not the typical form of collision. In the three accidents, where the speed in all has been low, the collision has occurred with a much narrower overlap between the buses.

CRASH BOX: The crash box is built into the floor under the driver's seat. The purpose is to transfer as much of the energy from the collision as possible from the front and past the driver.

The first part of the test was therefore to construct digital simulations that assume that only parts of the buses hit each other. A narrower impact point in the collision means that much more energy must be absorbed in a limited area.

– We chose to take the three accidents from Norway as a starting point. Here, thanks to the reports from the Accident Investigation Board Norway, we have detailed information about the extent of damage and mechanisms, says Nævestad.

The three accidents are the accidents at Nafstad in 2017, Tangen in 2021 and Fredrikstad in 2022. In working on the simulation, the two researchers looked at how large an area of ​​the front of the buses hit each other, what angle the buses hit each other, and what speed the buses had at the moment of collision.

Data from the accidents enabled the researchers to program the digital simulation so that the result was similar to what is described in the accident reports.

The next step in the project was to investigate what design changes could reduce the risk to drivers in these types of collisions. The result was a steel frame that protects the area where the driver sits, a crash box or safety cage.

The point of the design is to direct energy from the collision to the area behind the driver. “When a passenger car collides, a lot of the energy is captured by the front of the vehicle. That’s where you have the engine and the axle, among other things. In a bus, the driver sits in front of the axle, and there’s no engine in front of him either. So when a bus collides, it’s the driver who takes the impact,” says Nævestad.

MAKES ROOM FOR SURVIVAL: The illustration shows how two buses, each with its own crash box, will be affected by a collision where both buses are traveling at 30 kilometers per hour. The overlap between the two buses is 15 percent, and they hit each other head-on (0 degree angle). The illustration on the left shows the situation just before the collision, while the illustration on the right shows the situation at the moment of collision, 130 milliseconds into the impact. According to this simulation, the drivers will not have the steering wheel pressed completely into their torso. On the bus with the yellow crash box, the steering wheel has moved 32.7 cm at the same time as the seat has moved 18.6 cm forward. In the bus with the green crash box, the steering wheel has been pressed 25.7 cm towards the driver, while the seat has been pressed 18.6 cm forward.

According to the researchers, the crash box is about transmitting the energy further into the bus to materials that can absorb the energy through deformation.

– The point is to keep the survival space for the driver intact and instead send the energy backwards in the bus towards the axle.

The digital tests of the crash box show that the solution can reduce how far the steering wheel is pressed against the driver in a collision. The simulations show that the solution proposed in the report contributes to a reduction of 50–60 percent. This may in several cases be decisive in determining whether the injuries become life-threatening.

WITH AND WITHOUT: On the left is a simulation of how an accident pushes the steering wheel into the driver's area. In the simulation, both buses are traveling at 30 kilometers per hour, the buses hit each other at a 0 degree angle with an overlap of 15 percent. In the illustration on the left we see the result without a crash box, and on the right we see the result with a crash box.

The researchers behind the report now hope that the findings can inspire bus manufacturers as they work to improve safety.

– They will probably find their own solutions, but we hope that this can be an inspiration. In addition, the UN is also working on developing new security standards, and this report illustrates a little of what can be achieved, says Nævestad.