MOTORCYCLE DESIGN

Improvements to the design and construction of cars over the last 10 or 20 years have resulted in very substantial reductions in deaths and injuries on the road. This has not been the case with changes to the design of motorcycles.

Engine Size

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 of 200 mph and more.
The In-depth study of motorcycle accidents59 showed that riders 100 – 250 cc motorcycles tended to be younger and riders of 500 cc and over machines tended to be older riders. Riders of motorcycles of 600 cc and above were more likely to be involved in crashes on bends, and riders of motorcycles with 900 cc and above were more likely to be involved in overtaking or filtering accidents.

The TRL study of motorcyclists deaths between 1994 and 200260 found that large motorcycles were more likely to have travelling excessively fast than smaller motorcycles, and their riders were more likely to have been riding poorly, before their fatal crash. Riders of smaller machines were more likely to have judged their own path poorly.

A 1988 TRL report61 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.

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.

New Zealand law restricts motorcyclists with a learner or restricted licence to riding motorcycles with an engine capacity of 250cc or less. A study62 of its effects found no consistent pattern of risk increasing with the cubic capacity of the motorcycle, and suggested that cubic capacity is a poor measure of engine power. The findings suggested 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.

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.

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.

Having said that, there is little justification for manufacturer’s producing such powerful motorcycles (or cars, of course) that are capable of speeds of more than twice the maximum speed limit for road use.

There is on-going research and development of intelligent speed adaptation 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.

Braking
Braking, especially in an emergency, is one of the most difficult tasks encountered when riding a motorcycle. Errors in braking 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). Some manufacturers are now fitting Combined Braking Systems (CBS) that operate both brakes and distribute the braking force to the front and rear wheels to improve stability when braking

TRL research12 shows that the incorrect use of motorcycle brakes is considered to be a factor in many motorcycle 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.

ABS
ABS brakes for motorcycles have been commercially available since 1988, and are now being fitted to a wide range of machines. 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.

It is important to ensure that riders understand how advanced braking systems work and receive training in their use. Training courses to help riders to become accustomed to ABS technology and its advantages should be encouraged. For example, a scheme similar to the Bosch ESP-erience could help in raising the awareness.

Publicity needs to encourage riders to invest in machines with ABS to help the spread of this technology. A high level of fitment of ABS should be seen as an important step forward in motorcycle safety in future. The government would like to see wider implementation of these systems on all motorcycles.

Daytime Running Lights
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 permit, but do not require, the use of daytime running lights by any vehicle, not just motorcycles. However, research into daytime running lights on motorcycles (and on all motor vehicles) is somewhat contradictory at present.

In tests of motorcyclists’ daytime conspicuity64 the best results were from motorcycles using a 40W large headlamp (dipped) or a pair of daytime running lights.

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.11 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.

A study in Singapore65 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

A report by the SWOV Institute in the Netherlands66 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%.

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.12 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.

Some motorcycle manufacturers are now fitting automatic headlamp on systems so that the motorcycle’s lights are always on, a move which RoSPA supports.

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.

The Government 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.

Leg Protectors
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.

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.

TRL research12, 67 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.

However, crash tests conducted by the International Motorcycle Manufacturers Association11 produced 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. A later series of tests by the same organisation found that leg protectors were beneficial in 2 out of 7 tests, detrimental in 4 out of 7 test and made no difference in one test. Further tests by TRL reached the opposite conclusion, finding ‘substantial benefits’, and recommended further development and research.

Airbags
Airbags are well-established for cars, but not so for motorcycles. Some research estimates that 25% of serious leg injuries, and up to 40% of serious and fatal head injuries, might be prevented by airbags.

There are many problems with applying airbag technology to motorcycles. The riders and vehicles vary widely in mass, the seating position of the rider, and the diversity in motion of both the rider and motorcycle, will all affect the outcome of the collision. There can also be compatibility problems between the airbag and the rider’s helmet, due to helmet shapes also having wide design variations, which can result in a severe neck injury.

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).

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 reasons11.

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.

The European Experimental Vehicles Committee report69 reviewed 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.

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

However, technical solutions will be developed. Eventually, sensors will record the rider’s position and weight and the impact speed, so that an adaptive airbag would deploy to protect the rider if the circumstances warranted it, having taken these variables into account. Airbags have the potential to reduce the severity of head, neck and torso injuries, which are the areas of a motorcyclist’s body that are most at risk from suffering a fatal injury. When the technology is ready, manufacturers should be encouraged to fit airbags as standard through the range of bikes.

Tyres
The tyres are the only part of the motorcycle in contact with the road. The type and condition of tyres on a motorcycle have a significant effect on the vehicle’s handling, steering, cornering, braking and stability. It is essential that the correct type of tyres is used and they are kept in a good condition at the correct pressure all the time and replaced as soon as necessary.

Many manufacturers recommend specific tyres for their motorcycle. This ensures that the most suitable type of tyre for that particular machine is used, and riders should always use tyres recommended by the manufacturer when replacing them. It is also important that the tyres are suitable for the speed capability of the motorcycle and its load capacity.

Tyres need to be kept at the correct pressure (which may vary depending on whether a pillion passenger and/or fully loaded panniers are being carried). Over-inflated or under-inflated tyres will affect the safe handling of a motorcycle and may contribute to an accident. Tyre pressures should be checked at least once a week. Good tread depth is also crucial, especially in the wet. In the UK, the minimum tread depth for motorcycles over 50 cc is 1mm across ¾ of the width of the tread pattern and visible tread on the remaining ¼. For motorcycles up to 50 cc, all groves of the original tread pattern must be visible.72 However, it is also important to replace tyres before they reach the minimum tread depth, and many have tread wear indicators in the tyres to show when the tyre should be replaced. Tyre manufacturers recommend a minimum tread depth of 2 mm

A concern increasingly expressed is that there appears to be a thriving after-market of products and services to help motorcycle owners adapt their motorcycles after they have purchased them. These adaptations often significantly change the capabilities and handling of the machines, which the rider may not fully understand or e able to cope with in all situations

Motorcycle Design - Conclusion
Motorcycles are complex, powerful vehicles that have improved immensely over recent years. However, some of these improvements require further development and there remain a number of areas where the safety performance of motorcycles could be further improved.

In its Motorcycling Strategy, the Government has said that it will consider the potential for a consumer information assessment programme for motorcycles to assess whether it might lead to improvements in motorcycle safety in the way that the EURONCAP programme has led to significant improvements in car design.

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