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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.
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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.
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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.
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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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