RoSPA – 7. The Design Of Motorcycles


7.1 The term motorcycle encompasses a wide variety of vehicles, from small low-powered mopeds and scooters to large, high powered motorcycles capable of reaching speeds approaching 200 mph. Learner riders are restricted to motorcycles of 11kw power output and recently qualified riders to 25kW for the first two years.

7.2 The design and construction of motorcycles can affect both primary and secondary rider safety. The main primary safety features are the motorcycle’s handling characteristics: engine power, speed, lighting and braking capabilities. (Other crucial safety areas are the stability, handling and tyres of the vehicles. However, there does not appear to be any significant safety concerns in these areas on modern motorcycles). The main secondary safety features are leg protectors and airbags.

7.3 Engine Size

7.3.1 A 1988 TRL report used a special STATS19 monitoring project that recorded the engine size of accident-involved motorcycles between 1984 and 1986, along with National Travel Survey data and data on the number of registered motorcycles to explore the relationship between engine size and casualty rates. There were marked differences in the use of motorcycles of different engine sizes. Larger machines did more of their mileage on non built-up roads, tended to be ridden by older riders, were more likely to carry pillion passengers and were used more in the Summer than the Winter months.

7.3.2 The study found that accident rates per kilometre travelled fell with increasing engine capacity, possibly because larger machines tended to be used by more experienced riders. However, riders of larger machines were more likely to be killed or injured than riders of small machines. In particular, increased engine size was associated with a higher proportion of accidents and casualties on non-built up roads. Riders of more powerful motorcycles also tended to have a higher proportion of accidents at night, and while going ahead on a bend or while overtaking.

7.3.3 New Zealand law restricts motorcyclists with a learner or restricted licence to riding motorcycles with an engine capacity of 250cc or less. A recently published study assessed compliance with the law; whether the risk of an injury crash was increased for learner/restricted licence holders who do not comply with the regulations; and whether the risk of an injury crash increases with increasing capacity of the motorcycle. A population-based case-control study was conducted over a three year period from February 1993. It found no consistent pattern of risk increasing with cubic capacity, and suggested that cubic capacity is a poor measure of engine power. The findings suggest that if cubic capacity was to remain the sole basis for restricting learner and restricted licence holders, consideration should be given to having a substantially lower capacity than 250cc.

7.3.4 In the 1960s and 1970s, most sports motorcycles were capable of producing 40 – 50 bhp with top speeds of 115 -120 mph. Today, outputs of 75 – 90 (even 130) bhp, with top speeds not far short of 200 mph, are quite common. It is inevitable that many riders will want to use the machine’s maximum capability and to test their vehicle’s limits. Even within legal speed limits, such powerful machines require exceptional levels of skill.

7.3.5 In the early 1990’s a proposed European Commission limit of 100 bhp on motorcycles failed, partly because it was not possible to demonstrate a link between bhp and accident risk. Therefore, it was not possible to show that imposing a limit would reduce the number of motorcycle accidents.

7.3.6 Having said that, there is little justification for manufacturer’s producing such powerful motorcycles (or cars, of course) which are capable of speeds of more than twice the maximum speed limit for road use. Recent reports suggest that manufacturers are considering setting a voluntary maximum limit of 186 mph on motorcycles. But setting a limit at this excessive speed does not seem to be a serious attempt to improve rider safety.

7.3.7 There is on-going research and development of intelligent speed adaption devices for cars that would limit their top speed to the speed limit of the road on which it was driving. This development process could also be applied to motorcycles, although any such devices will need to be specifically designed for two-wheelers and not simply transferred from four wheel vehicles.

7.4 ABS (anti-lock braking systems)

7.4.1 Braking, especially in an emergency, is one of the most difficult tasks encountered when riding a motorcycle. Errors in braking a motorcycle can easily lead to skidding, capsizing or the vehicle becoming unstable. Front and rear motorcycle brakes are usually operated separately (unlike a car’s which are linked) and so the rider has to decide which brake to apply, when and what proportion of front and rear braking to use according to the situation and road surface (some motorcycles do have coupled brakes).

7.4.2 TRL research shows that the incorrect use of motorcycle brakes is considered to be a factor in many TWMV accidents. Over a third of riders used only the rear brake and 11% used only the front brake. Even in an emergency, 19% of riders only used their rear brakes and 3% only used their front one. One study estimated that correct braking, using the full braking capability of the motorcycle, could prevent 30% of motorcycle accidents, although this study was conducted before ABS was available for motorcycles.

7.4.3 ABS brakes for motorcycles have been commercially available since 1988, and have been fitted to a limited range of large, powerful and expensive motorcycles. The cost of these systems means that it is uneconomic to fit them on smaller, less expensive machines. However, a TRL project to develop an ABS system for lightweight motorcycles suggests that it is feasible to produce a cost-effective system for smaller machines, and three manufacturers have offered small motorcycles with optional ABS. It should be noted that the characteristics of braking systems for motorcycles are different from those of cars; and in particular, it is not possible to steer when applying ABS brakes on a motorcycle. The DETR believe that ABS should eventually become standard fitment on all motorcycles.

7.5 Daytime Running Lights

7.5.1 Drivers involved in a collision with a motorcycle often claim that they did not see the motorcycle. It has been suggested that motorcyclists should be required to use their headlights during the day as this may help to reduce accidents. The Road Vehicles Lighting Regulations 1989 (as amended) currently permit, but do not require, the use of daytime running lights by any vehicle, not just motorcycles. However, the conclusions of research into the benefits or dis-benefits of daytime running lights on motorcycles (and on all motor vehicles) is somewhat contradictory at present.

7.5.2 A review of literature on the effectiveness of daytime running lights for motorcycles is contained in the European Experimental Vehicles Committee report on motorcycle safety. It states that a study in four US states showed a reduction of 41% in accidents during daytime following a law requiring daytime use of motorcycle headlights.

7.5.3 A study in Singapore found that the introduction of daytime running lights for motorcycles in 1995 has reduced the number of fatal and serious injury accidents, although had no significant effect on slight accidents.

7.5.4 A report by the SWOV Institute in the Netherlands indicates that the introduction of daytime running lights in Austria reduced motorcyclist casualties during the day by 16%, and estimates that the Europe-wide introduction of a similar law would reduce motorcyclist casualties in the EU by around 7%.

7.5.5 However, road trials by TRL in the early 1990s found that over 70% of motorcycles in Great Britain were fitted with headlamps that were ineffective as a conspicuity aid either by day or night. This suggests that there would be little benefit in motorcycles using their normal headlights during the day. Specifically designed daytime running lights (separate from the normal headlights) may be more effective.

7.5.6 Some countries are considering the mandatory introduction of the use of daytime running lights for all vehicles. However, there is concern that this may adversely affect motorcyclists, in that if all vehicles use headlamps during the day, the relative conspicuity of two-wheelers will be reduced.

7.5.7 The UK government currently has no plans to introduce mandatory daytime running lights for motorcyclists or for all vehicles, and would only consider this option if it was supported by evidence of its likely effectiveness, and after considering any increased environmental costs (in CO2 terms) due to the energy to power the lights. However, the Highway Code does advise motorcyclists that using dipped headlights in daylight may increase their conspicuity.

7.6 Leg Protectors

7.6.1 Leg injuries account for approximately 60% of serious injuries to motorcyclists, and frequently lead to permanent disability. Leg protectors have been suggested as a way of reducing such injuries. Leg protecting fairings have been shown to reduce injuries but may also alter the motion of the motorcycle during and after an impact and it is, therefore, important to ensure that any changes proposed do not increase the risk of injury.

7.6.2 Research has resulted in contradictory claims for the efficacy of leg protectors, with some studies suggesting that they would reduce leg injuries, but others suggesting that they might even increase the risk of other injuries.

7.6.3 TRL research over a number of years has investigated whether leg protectors would significantly reduce the incidence and severity of leg injuries to motorcyclists. Crash tests of different types of motorcycles, with and without leg protectors, were designed and conducted by TRL. They concluded that leg injuries would have occurred in 55% of the crash tests on motorcycles without leg protectors, but in only 12% of those with leg protectors. They also concluded that the leg protectors used would not have increased the risk of head injuries, and in some cases actually showed potential for reducing them.

7.6.4 However, crash tests conducted by the International Motorcycle Manufacturers Association produced very different results, in which leg protection was found to be beneficial in three out of eight pairs of tests, but detrimental in five pairs of the eight tests. Overall, this study concluded that leg protectors increased the net risk of head and leg injuries.

7.6.5 The European Experimental Vehicles Committee Report on Motorcycle Safety noted that the design and construction of leg protectors has evolved and improved in recent years. The DETR believes that research has shown that leg protectors and airbags (either individually or as a combination) will reduce accident severity. However, independently tested and appropriate designs for particular models of motorcycles need to be produced.

7.7 Airbags

7.7.1 Airbags are now well-established for cars, but research into motorcycle airbags is still at an early stage. Some research estimates that 25% of serious leg injuries, and up to 40% of serious and fatal head injuries, might be prevented by airbags.

7.7.2 Airbags in cars are designed to absorb impact, whereas motorcycle airbags need to absorb (or partially absorb) impact and influence the trajectory of the rider (in order to raise the rider’s head above the edge of the car roof and to direct the rider’s body upwards to reduce the impact against the side of the car).

7.7.3 Motorcycle airbags need to be deployed more quickly (within the first 20ms of an impact) than car airbags and the impact detection systems that trigger a car airbag cannot be used on motorcycles for various reasons.

7.7.4 Motorcycle accidents involve a wide range of impact configurations, including frontal impacts where the motorcycle strikes an object head-on and side impacts where a vehicle strikes the motorcycle. Motorcycle airbags are likely to be useful in collisions of a motorcycle into the side or rear of another vehicle, and in oblique angle impacts.

7.7.5 The European Experimental Vehicles Committee report reviews a range of impact tests in which medium sized motorcycles were run into cars. Where airbags were not used the head of the dummy impacted against the edge of the roof. In tests with airbags the change in trajectory meant that head contact with the car was avoided completely, and the motorcyclist’s body deflected into a higher movement path.

7.7.6 Not all research has been so positive. Some has suggested that airbags may increase injuries, particularly to the neck.

7.7.7 Motorcycle airbags are likely to be most beneficial in lower speed impacts, up to 30 mph. As with any safety system, there will be impacts that exceed the ability of the airbag to protect the rider. Overall, initial research suggests that appropriately designed motorcycle airbags may be beneficial in reducing injuries to motorcyclists, but further research and development is required to produce effective, practical and affordable systems. Such research is being undertaken by both Honda and Yamaha as part of the Japanese Government’s Advanced Safety Vehicle initiative.

7.8 The Design of Motorcycles – Conclusion
Motorcycles are complex, powerful vehicles that have improved immensely over recent years. However, some of these improvements have created new hazards, and there remain a number of areas where the safety performance of motorcycles could be further improved.