A large quantity of data was collected to describe the use and performance of the helmets involved in the motorcycle accidents. The analysis included an investigation of the helmet performance and an analysis of the detailed information on injuries. The results of this analysis then provided an adequate measurement of helmet effectiveness in preventing or reducing head injuries.
Helmet use and performance
Table 10.1.1 shows the distribution of helmeted and unhelmeted riders and passengers. A mandatory helmet use law was in effect in Thailand at the time this study was conducted. Helmets were worn by two-thirds of the riders but only 29% of passengers in the Bangkok accident population. Of the 475 helmets worn by accident-involved motorcycle riders, 128 (27%) were acquired for further examination. In addition, 17 of the 69 accident-involved passenger helmets were also obtained for further analysis.
Table 10.1.1: Helmet use by motorcycle riders and passengers
Motorcycle rider Motorcycle passenger Helmet use
Frequency Percent Frequency Percent
No 248 34.30 168 70.89
Yes 475 65.70 69 29.11
Total 723 100.0 237 100.0
Head injuries were far less frequent among helmeted riders, particularly if the helmet remained in place on the rider’s head. Less than 4% of riders whose helmets remained on had any kind of head injury, and only 10 (one in 36)
suffered a brain injury. By comparison, unhelmeted riders were nearly five times as likely to sustain head injury (17.7% versus 3.6%). Head injuries above the “Minor” level were almost all brain injuries, and unhelmeted riders were almost 4 times as likely to suffer head injury in the “Moderate-to-Fatal” range: 10.9% versus 2.8%, and 6 times as likely to sustain life-threatening head injuries in the “Severe-to-Fatal” range: 6.9% versus 1.1%.
Riders whose helmets ejected seemed to come out the worst of all, even worse than unhelmeted riders. This is partly due to the fact that riders whose helmets ejected were more likely to sustain impacts to the head or face than unhelmeted riders, and the impact – sometimes very severe – may have caused the helmet to come off. In other words, head impact and helmet ejection are mixed together as cause and effect. If head or face impact occurs, head injury and helmet ejection may result, and helmet ejection then allows additional head injuries. Helmet ejection is discussed in greater detail in section 10.4.
Table 10.1.2 shows a cross-tabulation of helmet use and head injury severity. Approximately 47% (118/248) unhelmeted riders had no head injury compared to 64% of helmeted riders (305/475). Also 12% (30/248) of unhelmeted rider had AIS over 1, compared to 7% (34/475) for helmeted riders. For life threatening injuries (severe to fatal) approximately 10% (24/248) of unhelmeted versus 5% (24/475) of helmeted. Table 10.1.2 omits one helmeted rider who suffered brain injuries at the “critical” level, but whose helmet status (ejected or retained) was unknown.
Table 10.1.2: Rider helmet use and severity of most severe head injury
Helmet worn No helmet
Ejected Retained Total Most severe
head injury
Freq % Freq % Freq % Freq % None 204 82 70 63 351 96 625 86 Minor 17 7 21 19 3 1 41 6 Moderate 3 1 3 3 4 1 10 1 Serious 7 3 2 2 2 1 11 1 Severe 12 5 13 12 4 1 30 4 Critical 3 1 1 1 0 0 4 1 Fatal 2 1 0 0 0 0 2 0 Total 248 100 110 100 364 100 722 100
A separate analysis was done on a case-by-case basis, relying on the investigator's subjective evaluation of helmet performance. This is because the relationship between helmet use and head injury can vary from accident to accident. For example, in one accident a rider might have no head injury because there was no impact to the helmet or the head. In another case, a rider might have serious head injury, yet extensive damage to the helmet might show that it prevented far more severe (or even fatal) head injuries. In a third case, a
unprotected face -- in which case the helmet would be judged to have had no effect on head injury. Other possibilities include situations in which a helmet flies off the rider's head, performs very badly or is completely overwhelmed by impact loads. In these cases, the helmet performance might be judged as having "no effect" on head injury.
The results of this analysis are shown in Table 10.1.3. One third of the helmets showed no sign of contact. Of the 330 helmets that showed evidence of collision damage, the helmet was judged to have prevented head injuries completely in half those cases. The helmet reduced head injury in another one- third (103 cases) in which it sustained collision contact.
Table 10.1.3: Helmet effectiveness evaluation
Helmet effect Frequency Percent of total
Percent of group No helmet, injuries occurred 129 17.8 47.8 No helmet, no contact 118 16.3 52.2 Unhelmeted subtotal 247 34.2 100.0 Helmet worn, no effect on injuries 65 9.0 13.7 Helmet worn, reduced injuries 103 14.2 21.7 Helmet worn, prevented injuries 162 22.4 34.2 Helmet worn, no contact 144 19.9 30.4 Helmeted subtotal 474 65.6 100.0
Unknown 2 0.3 -
Total 723 100.0 100.0
Table 10.1.4 shows the helmet use for the 50 fatal riders within the 723 on-scene, in-depth accident cases. The helmet was worn by two-thirds of non- fatal riders but it was worn in less than half of fatal cases.
The majority of fatally injured riders (54%) were unhelmeted. Of 23 helmets worn, only seven (30%) were retained on the rider’s head to the end of the collision sequence. Six helmets were ejected because they were not fastened properly, and two because of extensive rider facial injuries (a shattered jaw can allow the chin strap to slip off.) However, seven of the 16 ejected helmets came off because of structural failures of the shell or retention system. Most fatal accidents are high-energy collisions that would severely test the best of helmets.
It should be noted that the rider fatalities were not due exclusively to head injuries; many fatally injured riders had life-threatening injuries of the chest, abdomen or pelvis. Two were run over by other vehicles (one a bus), a situation in which death is very likely, with or without a helmet.
However, the advantage of the helmet was still obvious in many ways. For example, in several of the fatal accidents, the unhelmeted riders suffered a skull fracture to an unprotected part of the head while they were involved in a low energy collision, such as a fall and tumble on the pavement.
Table 10.1.4: Type of helmet in fatal and non-fatal accident
Non-fatal accident Fatal accident Helmet type
Frequency Percent Frequency Percent
No helmet 221 32.8 27 54.0
Not motorcycle helmet 14 2.1 1 2.0 Half/Police-type helmet 138 20.5 12 24.0
Open-face helmet 87 12.9 3 6.0
Full-face helmet 213 31.6 7* 14.0
Total 673 100.0 50 100.0
*Two riders were run over by another vehicle.