Memorandum by Gloucestershire County Council
Road Safety Unit (RTS 25)
ROAD TRAFFIC SPEED
SPEED RELATED
ACCIDENTS
Before we can understand the relationship between
road traffic accidents and speed, we first need to consider the
part played by kinetic energy. In all but a small minority of
reported accidents, it is the kinetic energy of the bodies involved
that is responsible for the damage and injuries sustained. Furthermore
the greater the speed of the objects in collision, the greater
the kinetic energy and the greater the potential that injury and
damage will be sustained.
We might conclude therefore that all accidents
are speed related. This is not very helpful however since it is
not the kinetic energy itself that causes the accident, but a
failure to manage the kinetic energy in a manner that is safe.
In Gloucestershire, as with all other local
authorities across the country, we obtain our information about
road traffic accidents, from the national Stats 19 reporting system.
At the last major review in 1997, we agreed to take part in the
national trial of a new system for recording the cause of accidents.
The system is in two parts: A compulsory field in which the reporting
officer must indicate what went wrong (Precipitating Factor),
followed by up to four optional fields detailing why (Causation
Factors). During the year 2000 the following Precipitating Factors
were recorded for injury accidents in Gloucestershire:
| 1. | Failed to stop (mandatory sign)
| 49 |
| 2. | Failed to give way |
254 |
| 3. | Failed to avoid pedestrian
| 60 |
| 4. | Failed to avoid vehicle or object in carriageway
| 538 |
| 5. | Failure to signal/misleading signal
| 21 |
| 6. | Loss of control vehicle
| 360 |
| 7. | Pedestrian entered carriageway without due care
| 190 |
| 8. | Passenger fell in or near PSV
| 7 |
| 9. | Swerved to avoid object in carriageway
| 15 |
| 10. | Sudden Braking | 86
|
| 11. | Poor turn/manoeuvre |
233 |
| 12. | Poor overtaking | 76
|
| 13. | Drove wrong way (eg 1-way street)
| 8 |
| 14. | Operating door carelessly
| 9 |
| 15. | Other | 39
|
| | Total | 1,945
|
TABLE ONE:
PRECIPITATING FACTORS
With the exception of numbers 8, 9 & 15, in the above
table, the factors generally describe various forms of human error.
If we add them together we can conclude that 97 per cent of all
injury accidents in Gloucestershire during the year 2000, were
caused by human error.
So far therefore we know that accidents mostly result from
a failure to manage kinetic energy in a manner which is safe and
that (in Gloucestershire at least), in 97 per cent of cases human
error is to blame.
This mechanistic explanation however still does not explain
where speed enters the equation. What we are missing is responsibility,
why were the errors made. The second part of the national accident
causation trial allows for the reporting officer to make a judgement
about why the accident occurred. The following table shows the
causation factors attributed to injury accidents in Gloucestershire
during the year 2000.
ACCIDENTS WITHIN GLOUCESTERSHIRE FOR PERIOD 2000
ACCIDENT ANALYSIS BY CAUSATION FACTORS—CONFIDENCE
ALL LEVELS
| Code Causation Factor | CF1
| CF2 | CF3
| CF4 |
| 1 Impairment—Alcohol
| 86 | 9
| 10 | 6
|
| 2 Impairment—Drugs
| 8 | 4
| 0 | 3
|
| 3 Impairment—Fatigue
| 28 | 6
| 6 | 2
|
| 4 Impairment—Illness
| 13 | 10
| 1 | 0
|
| 5 Distraction—Stress/emotional state of mind
| 13 | 7
| 6 | 8
|
| 6 Distraction—Physical in/on Vehicle
| 14 | 9
| 5 | 1
|
| 7 Distraction—Physical outside vehicle
| 22 | 6
| 4 | 3
|
| 8 Behaviour—Panic
| 21 | 14
| 7 | 2
|
| 9 Behaviour—Careless/thoughtless/reckless
| 202 | 103
| 58 | 26
|
| 10 Behaviour—Nervous/uncertain
| 7 | 7
| 14 | 3
|
| 11 Behaviour—In a hurry |
27 | 34
| 22 | 16
|
| 12 Failure to judge other person's path or speed
| 325 | 131
| 52 | 11
|
| 13 Disability | 4
| 3 | 1
| 1 |
| 14 Failed to look | 158
| 114 | 38
| 13 |
| 15 Looked but did not see | 177
| 127 | 73
| 18 |
| 16 Inattention | 189
| 225 | 107
| 47 |
| 17 Person wore dark or inconspicuous clothing
| 3 | 14
| 11 | 4
|
| 18 Other (please supply details)
| 34 | 8
| 10 | 4
|
| 19 Crossed from behind parked vehicle etc
| 34 | 10
| 3 | 2
|
| 20 Ignored lights at crossing (Pedestrian)
| 3 | 4
| 1 | 2
|
| 21 Excessive speed | 103
| 93 | 47
| 27 |
| 22 Ignored lights at crossing (Vehicle)
| 8 | 6
| 3 | 1
|
| 23 Inexperience of driving | 26
| 49 | 27
| 10 |
| 24 Inexperience of vehicle | 4
| 10 | 12
| 10 |
| 25 Interaction or competition with other road users
| 3 | 4
| 4 | 3
|
| 26 Aggressive driving | 13
| 30 | 25
| 10 |
| 27 Lack of judgement of own path
| 63 | 98
| 71 | 45
|
| 28 Tyres—Wrong pressure |
1 | 0
| 3 | 0
|
| 29 Tyres—Deflation before impact
| 13 | 2
| 1 | 1
|
| 30 Tyres—Worn/Insufficient tread
| 3 | 1
| 3 | 1
|
| 31 Defective lights or signals |
1 | 4
| 3 | 0
|
| 32 Defective brakes | 13
| 3 | 1
| 3 |
| 33 Other (please supply details)
| 14 | 3
| 1 | 0
|
| 34 Site details—Poor road surface
| 4 | 6
| 4 | 1
|
| 35 Site details—Poor/No Street Lighting
| 1 | 4
| 4 | 5
|
| 36 Site details—Inadequate signing
| 1 | 0
| 2 | 1
|
| 37 Site details—Steep hill
| 1 | 4
| 5 | 3
|
| 38 Site details—Narrow road
| 4 | 12
| 8 | 1
|
| 39 Site details—Bend/Winding road
| 6 | 21
| 19 | 9
|
| 40 Site details—Road works
| 1 | 2
| 5 | 5
|
| 41 Slippery road | 46
| 43 | 32
| 25 |
| 42 High winds | 0
| 4 | 6
| 0 |
| 43 Earlier accident | 0
| 0 | 5
| 0 |
| 44 Other (please supply details)
| 10 | 8
| 6 | 1
|
| 45 View—Windows obscured |
3 | 2
| 1 | 0
|
| 46 View—Glare from sun |
13 | 10
| 9 | 0
|
| 48 Surroundings—Bend/Winding road
| 7 | 13
| 13 | 14
|
| 49 Surroundings—Stationary or parked vehicle
| 14 | 10
| 15 | 6
|
| 50 Surroundings—Moving vehicle
| 1 | 7
| 4 | 1
|
| 51 Surroundings—Buildings, fences, vegetation etc.
| 2 | 5
| 4 | 1
|
| 52 Weather (eg mist or sleet) |
10 | 10
| 17 | 11
|
| 53 Failed to see pedestrian or vehicle in blindspot
| 7 | 11
| 10 | 8
|
| 54 Animal out of control | 7
| 7 | 1
| 0 |
| Qualifier Total at requested level | 1777
| 1330 | 805
| 383 |
| Total accidents no qualifiers | 168
| 615 | 1140
| 1562 |
| Total Accidents | 1945
| 1945 | 1945
| 1945 |
| Note: An accident may have 0, 1, 2, 3 or 4 causation codes)
|
TABLE 2: CAUSATION
FACTORS
In table 2, only item 21 relates directly to speed and in
this instance we are really talking about speed in excess of the
legal limit for the road. What is less easy to obtain from the
data is the more subjective assessment of accidents caused by
speeds within the legal limit but inappropriate to the circumstances
at the time.
The distinction between these two is important. The use of
excess speed is essentially an attitude problem and the use of
inappropriate speed is more of a skill/judgement deficit.
From the causation factor data we can see that excessive
speed (21), was selected on 270 occasions. This equates to 14
per cent of all accidents in the year and 6 per cent of all attributed
qualifiers.
To identify inappropriate speed however we need to look further
within the Stats 19 reports. Key fields might include:
— References to speed in the English language description
of the accident; or
— Accidents where the precipitating factor is loss
of control of the vehicle; or
— Accidents where causation factor 11 is reported,
(in a hurry); or
— Accidents where one of the vehicles is reported
to have skidded, Jack-knifed or overturned.
Analysis of the data for 2000 in Gloucestershire reveals
a further 613 or 32 per cent of accidents that meet the above
criteria in additional to the 14 per cent with causation factor
21.
To summarise: In Gloucestershire during the year 2000, 14
per cent of injury accidents were given at least one causation
factor as excess speed and a further 32 per cent were estimated
to have resulted from inappropriate use of speed.
URBAN V
RURAL
There is no specific field in the Stats 19 data, to identify
whether an accident took place in an urban or a rural environment.
It is general practice therefore to use the speed limit as a guide.
If the limit on the road where an incident takes place is 40mph
or below then the accident is generally classified as Urban, if
the limit is over 40mph then the accident is generally considered
to be Rural.
Using this rule the following results were obtained from
Gloucestershire data for the year 2000:
| Rural | Fatal
| Serious | Slight
| Total |
| Excess Speed (Qualifier 21) | 9
| 40 | 111
| 160 |
| Inappropriate Speed (as previously defined)
| 5 | 65
| 226 | 296
|
| Total | 14
| 105 | 337
| 456 |
| Urban | Fatal
| Serious | Slight
| Total |
| Excess Speed (Qualifier 21) | 1
| 20 | 89
| 110 |
| Inappropriate Speed (As previously defined)
| 3 | 44
| 270 | 317
|
| Total | 4 |
64 | 359
| 427 |
TABLE 3: SPEED
RELATED ACCIDENTS
RURAL V
URBAN
SPEED MONITORING
Each year in Gloucestershire a speed limit compliance survey
is conducted. The survey includes measurements at twelve sample
sites for each speed limit category. The following results were
obtained in 2000:
| Speed Limit | Percentage of Drivers complying with the limit
|
| 30 | 41 |
| 40 | 68 |
| 50 | 81 |
| 60 | 91 |
TABLE 4: SPEED
LIMIT COMPLIANCE
IN GLOUCESTERSHIRE
The data from this survey suggests that exceeding the speed
limit (in Gloucestershire at least), is a bigger problem in urban
areas than it is in rural areas. However the accident data in
table 3 does not correlate with this finding. We might conclude
therefore that the smaller number of drivers who exceed the speed
limit on rural roads, are at higher risk of involvement in an
accident than those who speed on urban roads. There may be some
substance in this argument. However there is probably also a tendency
to identify speed as a factor more frequently in accidents that
occur at higher speeds than lower speeds. Lower speed accidents
are more likely to be attributed to a manoeuvre violation even
if more effective management of speed might have prevented the
incident.
To develop this theory further we might consider pedestrian
accidents. During the year 2000 there were 260 pedestrian accidents
in Gloucestershire. In 60 per cent of these accidents the reporting
officer recorded precipitating factor 7 (pedestrian entered carriageway
without due care, driver/rider not to blame) and only 23 per cent
were given precipitating factor 3 (driver failed to avoid pedestrian,
pedestrian not to blame). There is arguable a case for drivers
to be held more responsible for the speed at which they drive
(even within the limit), in areas where pedestrians are present.
The notion that pedestrians are largely to blame for pedestrian
accidents is as much a cultural concept as a technical one.
SAFER CITY
PROJECT
One of the objectives of the Gloucester Safer City Project
was to engineer "appropriate traffic onto appropriate roads"
and then to control speeds more effectively on those roads where
higher proportions of vulnerable road users are present. The experience
from the Safer City Project is now being extended to the wider
urban environment of the Gloucestershire Central Severn Vale area.
RURAL SPEED
MANAGEMENT
The principles of the Safer City Project can also be applied
in rural areas and initiatives like Quiet Lanes are not too dissimilar
to the home zones and traffic calming concepts developed for the
urban environment. There is a good argument for a national lead
on rural speed limits. In Gloucestershire we are increasingly
introducing 50mph limits as an accident remedial measure on lower
grade A and busy B class roads in the county. Unfortunately it
is now possible in many situations to leave a 7.3m wide A or B
class road subject to a 50mph limit and enter a 5m rural lane
where the 60mph national speed limit applies. Under current legislation
we would have to raise orders and erect signs on many of the minor
roads in the county to resolve this situation. This would clearly
be impractical, apart from the resource implications the visual
intrusion from the signing would be unacceptable.
The report by Babtie Ross Silcock entitled: Development of
a Rural Road Hierarchy for Speed Management (Oct 2001), includes
on page 11, a useful template for a speed management hierarchy.
EDUCATION TRAINING
AND PUBLICITY
The main challenge in getting the anti speed message across
is that drivers are constantly receiving a subliminal message
that it is acceptable to speed. All drivers know that it is illegal
to break the speed limit, yet they also know that "they"
(ie the Police, Local Authorities and Government) do not stop
drivers from speeding. With the combined efforts of technology,
engineering and enforcement, it would be possible to stop all
speeding. This has never been attempted because the resources
and political will do not exist to force compliance. Furthermore
the message is reinforced by car manufacturers who all too frequently
market their products by associating speed with excitement and
prestige. It is anomalous that we have a national speed limit
of 70 mph and tolerate the sale of cars with speedometers graduated
to twice the legal limit and more. In theory no driver has a need
for information relating to speeds in excess of 70mph. We must
use our education training and publicity resources to change public
attitudes to speed. Our objective must be to encourage drivers
and riders to view speeding as selfish and socially unacceptable
behaviour.
David Radford
Road Safety Manager
January 2002
| 
