Motorcycle Accident Cause
Factors and Identification of Countermeasures
Source: A study conducted by the University of
Southern California (USC). With funds from the
National Highway Traffic Safety Administration,
researcher Harry Hurt investigated almost every
aspect of 900 motorcycle accidents in the Los
Angeles area. Additionally, Hurt and his staff
analyzed 3,600 motorcycle traffic accident
reports in the same geographic area.
Throughout the accident and
exposure data there are special observations
which relate to accident and injury causation
and characteristics of the motorcycle accidents
studied. These findings are summarized as
1. Approximately three-fourths of these
motorcycle accidents involved collision with
another vehicle, which was most often a
2. Approximately one-fourth of these
motorcycle accidents were single vehicle
accidents involving the motorcycle colliding
with the roadway or some fixed object in the
3. Vehicle failure accounted for less
than 3% of these motorcycle accidents, and most
of those were single vehicle accidents where
control was lost due to a puncture flat.
4. In single vehicle accidents,
motorcycle rider error was present as the
accident precipitating factor in about
two-thirds of the cases, with the typical error
being a slide out and fall due to over braking or
running wide on a curve due to excess speed or
5. Roadway defects (pavement ridges,
potholes, etc.) were the accident cause in 2% of
the accidents; animal involvement was 1% of the
6. In multiple vehicle accidents, the
driver of the other vehicle violated the
motorcycle right-of-way and caused the accident
in two-thirds of those accidents.
7. The failure of motorists to detect and
recognize motorcycles in traffic is the
predominating cause of motorcycle accidents. The
driver of the other vehicle involved in
collision with the motorcycle did not see the
motorcycle before the collision, or did not see
the motorcycle until too late to avoid the
8. Deliberate hostile action by a
motorist against a motorcycle rider is a rare
accident cause. The most frequent accident
configuration is the motorcycle proceeding
straight then the automobile makes a left turn
in front of the oncoming motorcycle.
10. Intersections are the most likely
place for the motorcycle accident, with the
other vehicle violating the motorcycle
right-of-way, and often violating traffic
11. Weather is not a factor in 98% of
12. Most motorcycle accidents involve a
short trip associated with shopping, errands,
friends, entertainment or recreation, and the
accident is likely to happen in a very short
time close to the trip origin.
13. The view of the motorcycle or the
other vehicle involved in the accident is
limited by glare or obstructed by other vehicles
in almost half of the multiple vehicle
14. Conspicuity of the motorcycle is a
critical factor in the multiple vehicle
accidents, and accident involvement is
significantly reduced by the use of motorcycle
headlamps (on in daylight) and the wearing of
high visibility yellow, orange or bright red
15. Fuel system leaks and spills were
present in 62% of the motorcycle accidents in
the post-crash phase. This represents an undue
hazard for fire.
16. The median pre-crash speed was 29.8
mph, and the median crash speed was 21.5 mph,
and the one-in-a-thousand crash speed is
approximately 86 mph.
17. The typical motorcycle pre-crash
lines-of-sight to the traffic hazard portray no
contribution of the limits of peripheral vision;
more than three-fourths of all accident hazards
are within 45deg of either side of straight
18. Conspicuity of the motorcycle is most
critical for the frontal surfaces of the
motorcycle and rider.
19. Vehicle defects related to accident
causation are rare and likely to be due to
deficient or defective maintenance.
20. Motorcycle riders between the ages of
16 and 24 are significantly overrepresented in
accidents; motorcycle riders between the ages of
30 and 50 are significantly underrepresented.
Although the majority of the accident-involved
motorcycle riders are male (96%), the female
motorcycles riders are significantly
overrepresented in the accident data.
22. Craftsmen, laborers, and students
comprise most of the accident-involved
motorcycle riders. Professionals, sales workers,
and craftsmen are underrepresented and laborers,
students and unemployed are overrepresented in
23. Motorcycle riders with previous
recent traffic citations and accidents are
overrepresented in the accident data.
24. The motorcycle riders involved in
accidents are essentially without training; 92%
were self-taught or learned from family or
friends. Motorcycle rider training experience
reduces accident involvement and is related to
reduced injuries in the event of accidents.
25. More than half of the
accident-involved motorcycle riders had less
than 5 months experience on the accident
motorcycle, although the total street riding
experience was almost 3 years. Motorcycle riders
with dirt bike experience are significantly
underrepresented in the accident data.
26. Lack of attention to the driving task
is a common factor for the motorcyclist in an
27. Almost half of the fatal accidents
show alcohol involvement.
28. Motorcycle riders in these accidents
showed significant collision avoidance problems.
Most riders would over brake and skid the rear
wheel, and under brake the front wheel greatly
reducing collision avoidance deceleration. The
ability to counter steer and swerve was
29. The typical motorcycle accident
allows the motorcyclist just less than 2 seconds
to complete all collision avoidance action.
30. Passenger-carrying motorcycles are
not overrepresented in the accident area.
31. The driver of the other vehicles
involved in collision with the motorcycle are
not distinguished from other accident
populations except that the ages of 20 to 29,
and beyond 65 are overrepresented. Also, these
drivers are generally unfamiliar with
32. Large displacement motorcycles are
underrepresented in accidents but they are
associated with higher injury severity when
involved in accidents.
33. Any effect of motorcycle color on
accident involvement is not determinable from
these data, but is expected to be insignificant
because the frontal surfaces are most often
presented to the other vehicle involved in the
34. Motorcycles equipped with fairings
and windshields are underrepresented in
accidents, most likely because of the
contribution to conspicuity and the association
with more experienced and trained riders.
35. Motorcycle riders in these accidents
were significantly without motorcycle license,
without any license, or with license revoked.
36. Motorcycle modifications such as
those associated with the semi-chopper or cafe
racer are definitely overrepresented in
37. The likelihood of injury is extremely
high in these motorcycle accidents-98% of the
multiple vehicle collisions and 96% of the
single vehicle accidents resulted in some kind
of injury to the motorcycle rider; 45% resulted
in more than a minor injury.
38. Half of the injuries to the somatic
regions were to the ankle-foot, lower leg, knee,
and thigh-upper leg.
39. Crash bars are not an effective
injury countermeasure; the reduction of injury
to the ankle-foot is balanced by increase of
injury to the thigh-upper leg, knee, and lower
40. The use of heavy boots, jacket,
gloves, etc., is effective in preventing or
reducing abrasions and lacerations, which are
frequent but rarely severe injuries.
41. Groin injuries were sustained by the
motorcyclist in at least 13% of the accidents,
which typified by multiple vehicle collision in
frontal impact at higher than average speed.
42. Injury severity increases with speed,
alcohol involvement and motorcycle size.
43. Seventy-three percent of the
accident-involved motorcycle riders used no eye
protection, and it is likely that the wind on
the unprotected eyes contributed in impairment
of vision which delayed hazard detection.
44. Approximately 50% of the motorcycle
riders in traffic were using safety helmets but
only 40% of the accident-involved motorcycle
riders were wearing helmets at the time of the
45. Voluntary safety helmet use by those
accident-involved motorcycle riders was lowest
for untrained, uneducated, young motorcycle
riders on hot days and short trips.
46. The most deadly injuries to the
accident victims were injuries to the chest and
47. The use of the safety helmet is the
single critical factor in the prevention of
reduction of head injury; the safety helmet
which complies with FMVSS 218 is a significantly
effective injury countermeasure.
48. Safety helmet use caused no
attenuation of critical traffic sounds, no
limitation of precrash visual field, and no
fatigue or loss of attention; no element of
accident causation was related to helmet use.
49. FMVSS 218 provides a high level of
protection in traffic accidents, and needs
modification only to increase coverage at the
back of the head and demonstrate impact
protection of the front of full facial coverage
helmets, and insure all adult sizes for traffic
use are covered by the standard.
50. Helmeted riders and passengers showed
significantly lower head and neck injury for all
types of injury, at all levels of injury
51. The increased coverage of the full
facial coverage helmet increases protection, and
significantly reduces face injuries.
52. There is no liability for neck injury
by wearing a safety helmet; helmeted riders had
less neck injuries than unhelmeted riders. Only
four minor injuries were attributable to helmet
use, and in each case the helmet prevented
possible critical or fatal head injury.
53. Sixty percent of the motorcyclists
were not wearing safety helmets at the time of
the accident. Of this group, 26% said they did
not wear helmets because they were uncomfortable
and inconvenient, and 53% simply had no
expectation of accident involvement.
54. Valid motorcycle exposure data can be
obtained only from collection at the traffic
site. Motor vehicle or driver license data
presents information which is completely
unrelated to actual use.
55. Less than 10% of the motorcycle
riders involved in these accidents had insurance
of any kind to provide medical care or replace