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Bicycle helmets significantly reduce the risk of severe head injuries when worn correctly

Nov 2020

Vehicle Technology

In the past, countless crash tests have been conducted – many of them by DEKRA – in order to test and illustrate the potential benefits of bicycle helmets in real-life accident scenarios.

As the use of e-scooters becomes more widespread, it becomes relevant to ask whether bicycle helmets can also have a pro-tective effect for users of these vehicles. To this end, three tests were conducted at the DEKRA Crash Test Center. The tests simulated a situation where a scooter crashed into a curb and the user, represented by a Hybrid III crash test dummy, subsequently fell off the scooter. The dummy had no protection in the first test, and wore a helmet in the second. In the third test, an airbag helmet – a highly practical and space-saving last mile mobility solution – was used.


The load placed on the head was measured using the standard sensor systems in the dummy. This involved measuring the acceleration levels that acted on the head. The acceleration figures were converted into the risk of injury using the head injury criterion value (HIC). Background: The human head is subjected to different forms of stress in every accident, some of which overlap. These include the translational and rotatory stresses that act mainly on the bone and brain mass. Depending on the stress to which the body is subjected, the brain mass may undergo relative displacement within the skull. This can lead to minor or severe injury. The dimensionless HIC has been developed to enable us to assess and compare the potential severity of different injuries.

In crash tests, this criterion is calculated using a dummy, or sometimes in a simulation. It is based on the connection between the level and the duration of the deceleration that acts on the head along every dimensional axis during an accident. The duration is key to determining the extent to which the accelera-tion influences the risk of irreversible cranial or brain injury. If the head briefly impacts against an object for around 15 milliseconds, the HIC15 value of 1,000 represents a 50 percent probability of irreversible injury. In case of a longer deceleration, relatively speaking, whereby there is no direct, hard head impact (duration approx. 36 milliseconds), the HIC36 value of 700 is used as the defining threshold for a 50 percent risk of intolerable, irreversible injury.

In the crash test with no helmet, the acceleration levels measured when the head impacted the ground were very high, with an HIC36 value of 5,282. This value would be expected to cause critical to fatal injury. In the second test, the dummy wore a bicycle helmet. This reduced the load on the head to an HIC36 value of 122, thus significantly reducing the risk of a severe head injury. In the third test, the air-bag helmet’s trigger algorithm detected the dummy’s fall, and the airbag was deployed. The HIC36 value of 169 measured in this test was also a clear indicator that the risk of a severe head injury when wearing such helmets is very low.

Since – unlike a sober person with normal reactions – a dummy does not execute any form of defensive reaction to a crash, such as using its hands to break its fall, the values measured in all the tests are at the high end of the expected range. Never-theless, the enormous potential for protection offered by a helmet or airbag helmet in any scenariois clear. The airbag helmet also shows signs of an ad-ditional effect that could not be reflected in the tests. According to a study by Stanford University, the large-volume airbag helps to reduce the risk of con-cussion compared to conventional bicycle helmets.

In summary, it is clear that, when worn correctly, bicycle helmets significantly reduce the risk of severe head injury in case of an accident – regard-less of whether said accident involves another party or is simply a fall that does not involve any other persons. In DEKRA’s car-versus-bicycle tests, the airbag helmet demonstrated significant vulnerabilities in terms of crash detection (see accident example, Car collides with bicycle ). These issues have also been reported in tests conducted by other institutes, so this cannot be assumed to be a one-off. In case of falls, however, the airbag was triggered with a very high degree of reliability and provided at least the same level of protection as a conventional helmet. The airbag helmet represents a potential alternative for anyone who does not want to wear a helmet because it might ruin their hair or does not match their own aesthetic ideals, and also for those who find a conventional helmet too cumbersome to wear on their way to work with various modes of transport.

However, the tests have also shown that bicycle helmets are not only a suitable form of protection for cyclists. They are also a legitimate safety measure for users of personal light electric vehicles, and should be worn for every journey. However, the tests also confirmed that while an old helmet is better than no helmet at all, the manufacturer’s specifications with regard to replacing a helmet once it has reached a certain service life should be observed in order to maintain the optimum protective effect. For the helmets included in the test, the recommended service life was three to five years. Helmets that undergo a lot of stress, such as children’s or teenagers’ helmets that are constantly being dropped, should generally be replaced more frequently. Manufacturers specify the date of purchase as the start of the service life; however, consumers should check the legally required date of manufacture printed inside the helmet before buying, and make sure that it has not been sat on the shelf or in the storeroom for too long.

The fit of the helmet is also important. As with shoes, this can vary depending on the manufacturer and the model. This makes it important to try on and compare different helmets before buying. Even the most expensive helmet that comes out on top in all the tests will be useless if it ends up not being worn because it does not fit properly, or if a poor fit prevents it from providing its full protective effect.

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