A study carried out by the Monash Accident Research Centre (MUARC) and the Alfred Hospital found that speed is a major risk factor for head injury. Results have to be interpreted cautiously because it’s an observational study, but speed appears to be strongly associated with likelihood of head injury, when a crash occurs. The study found that the risk of head injury was five (5) times greater when travelling at over 30km/h rather than at less than 20km/h. This would be the reason that sport cyclists around the world wear helmets, although that “safety” measure doesn’t appear to be successful, given their higher injury rates compared with every-day cyclists not wearing helmets.