Research from Statistics
| Author | Paul Harris |
| DOI | 10.1177/0032258X7905200311 |
| Date | 01 July 1979 |
| Published date | 01 July 1979 |
| Subject Matter | Article |
CHIEF
SUPERINTENDENT
PAUL
HARRIS
Avon
and
Somerset Constabulary
Motoring Correspondent
of
THE
POLICE
JOURNAL
RESEARCH
FROM
STATISTICS
Now that most Forces have adopted the new, detailed, statistical
form in connection with road accidents it is fairly clear that
additional work falls upon the already over-burdened police officer.
It
is perhaps, therefore, worth reflecting upon the uses which have
been made of statistics and the benefits which rnay follow from the
new detail. It is hoped that in the longer term additional completion
of forms will result in
data
leading to improved road safety. This in
turn
will allow a reduced operational commitmentdue to a steadying
or lowering of the national road accident rate. The information on
accidents supplied by Police is linked to other
data
sources relating to
the composition and flows of traffic, vehicle speeds and spacing,
weather, road features and various aspects of road user behaviour.
The comments which follow here show the uses to which statistics are
put and give some of the results of research so far.
ALCOHOL
AND
ACCIDENTS
The scope of this type of research has been widened since the
report of the Blennerhassett Committee. The monitoring of
blood/alcohol levels in fatalities continuesas do examinations of the
habits of the drinking driver in order to evolve effective counter
Drivers killed in accidents: proportions with SA Cabove the legal limit.
j:r
,"
-\><:---1>
lI
»>
__
'--
~
'"
./
,,30
'-
/-_./
<
",,/
-..
"
<:>
i
1966/7
..
..
70 71 "74
7.
Vd'
July 1979
271
measures. The table shows the trends for the years 1966 to 1976 of
blood alcohol concentrations in excess of the legal limit of drivers
killed in road accidents. The larger proportions relate to
car
drivers;
it seems
that
motor
cyclists are less likely to come into this category.
The
apparent
downward trend in 1976 should be considered with
care. It reflects the much greater
number
of
motor
cyclists killed in
comparison with the number of car drivers to produce amis-leading
drop
on the graph.
It
can also be seen that the most significant age
group
is made up of 20 to 40 year olds. The figures are
much
worse
for
the peak periods of 10 p.m. to 2 a.m. on Fridays and Saturdays
II
Above 80mg/1.00ml
1\
Accident group
/
'\
7
'\
//
"
'-.1\
.-.....
/ I
• I
tL"
__
~
_
';o",rol
group I
~
~
I~-!
!
BA C distributions by the time
of
day
for
males and females combined.
100
20
60
~
c
"
!:
: 40
80
0600 1000 1400 1800 2200 0200
0600
Time
of day
II
"T
150mg/l00ml
I
1/\
Accident group
II\
/
~
/c'r~'\
~
-
....
.
....
.c:::_
_......
--
100
80
..
60
'"
J!
e
"
!:
..
..
40
20
o
0600
1000 1400 1800 2200
0200
0600
Time
of day
272 July 1979
which show that two-thirds of drivers killed have a blood alcohol
concentration in excess of the legal limit and one fifth are above the
level of 200mg/ 100mi. Alcohol also seems to be related to other road
users killed in accidents.
For
every driver who dies in an accident in
which at least one driver is positively breathalysed, more than double
that number of passengers and even more pedestrians are killed.
Coroners' reports indicate that between I in 4 and I in 5 of pedestrian
fatalities involve blood alcohol contents in excess of 80mg/ 100mi.
Alcohol of course is fairly straight-forward both in its effects and in
the ease with which its presence can be detected. Other drugs can be
much more complex. Both their variety and range of effects on
different individuals are vast. The situation is worsened by an
appreciation that drugs are often taken for the release or ease of
symptoms which themselves may impair the driving function.
Despite the fears of the potential danger expressed in many recent
medical reports it seems unlikely that any satisfactory progress will
be made.
NATURE
AND
SEVERITY OF
INJURY
The patterns of severe and fatal injuries associated to 5000 road
users have again supported the arguments in favour of seat belts.
Inclusion of uninjured as well as injured vehicle occupants has
provided more accurate assessments of alleviation of injuries due to
seat belts. The main conclusions relating to seat belts of current
design are shown as they may be of particular value to road safety
officers. Seat belts reduce the number of serious injuries by nearly
one half and fatalities by two-thirds.
They reduce the risk of injury for all impact directions, though
they are less effective in side impacts, where intrusion into the vehicle
interior has an .adverse effect.
Seat belts are particularly effective in reducing head injuries. The
head still remains the most important region of the body for which
further protection measures need to be developed and second in
importance for belted occupants is the chest region. Where injuries
did occur to belted occupants they were usually associated with
occupants to vehicle contact, exacerbated by intrusion into the
passenger compartment. The most common causes of injury are: in
frontal direction of the impacts, head and chest due to contact with
the steering wheel; in side impacts, contact with the side of the
compartment.
Although neck injuries were slightly more frequent for belted than
unbelted occupants, the injuries were of low severity and the majority
were simply stiffness of the neck. No fractures or dislocations of the
neck occurred.
Belts also offer protection by preventing the wearer from being
thrown out of the vehicle.
Just
underaquarter of unbelted occupants
thrown out were killed and this accounted for nearly half of all
deaths. Inertia reel belts and static belts are equally effective, but reel
July 1979 273
belts are more likely to be worn.
There was no evidence to suggest the wearing of belts in open cars
which overturned had a detrimental effect.
The risk of being trapped inside a vehicle which either caught fire
or submerged in water was minimal.
Many interesting features result from research into injuries
sustained by "unprotected" road users, i.e. pedestrians, pedal cyclists
and motor cyclists. Some of the more important are that three
quarters of pedestrian casualties result from impact with cars, largely
with their leading edges; one third of motor cycle and pedal cycle
injuries are caused by riders falling off their machines and one half
from collisions with cars.
URBAN CONGESTION SURVEYS
Surveys of traffic speeds, flows and parkingdensities were made in
1963, 1967,
1971
and
1976 in 13 urban areas in England in order to
monitor long term trends in traffic characteristics. The data have
taken account of journey speeds, passenger car unit flows and on-
street parking densities. The widely held belief that urban traffic is
grinding to a halt is belied by some striking features in these surveys.
Urban speeds, flows and parking densities on
wnkdays,
1967,
1971,
1976
Off·peak
periods Peak periods
1967 1971 1976 1967 1976
Whole towns
Average speed
(km,h)
32 33 36 29 29 32
Average
flow
(pcuihl
1230 1285 1265 1660 1765 1775
Parked
vetuctes/krn 17 14 10 10 I76
Central areas
Average speed
(km/hl
19 22 23 16 19 21
Average
flow
lPcu/h)
1350 1395 1385 1610 1715 1735
Parked vemctes/km
3.
2'
14 20 12 7
Overall traffic flows have increased slightly compared with the
estimated 38 per cent increase in total travel in Great Britain while
there has been a marked reduction in parking density, especially in
central areas. Perhaps due to the reduction in parking along with
road improvements
and
other traffic management measures average
speeds have shown asteady increase despite the additional flows
recorded.
URBAN
TRAFFIC
STUDIES
The aim of research into traffic behaviour in urban areas is to help
traffic engineers towards the best ways of using the road networks,
principally those
that
already exist. The travel needs of vehicle users
and pedestrians need to be balanced against the economic,
environmental and social costs oftravel. In meeting the whole needs
of the community methods of design must be shown to be convenient
and
accurate
and
the effects which changes have on traffic
274 July 1979
distribution need to be scientifically assessed. Urban environments
of course lend themselves to computer application and these
electronic aids are being used to monitor vehicle movements,
pedestrian demand, bus usage and the effects of bus priorityschemes,
and
the linking of traffic signals to improve flows. Super-imposed are
efforts to evaluate behaviour patterns resulting from schemes which
often encourage asubstantial number of drivers to seek alternative
routes.
ROAD
DESIGN
Traffic capacities and delays at road junctions depend on the
geometric properties of the junction and traffic demand. Emphasis
on junction design is continuing and safety is also now being
considered as a priority factor. The influence of other road design
features such as barriers and street lighting is being included to
provide more information on the choice of junctiontype and general
improvements in geometric design. Procedures have been developed
for calculating the capacity of individual entries to roundabouts
from a knowledge of geometric layout and traffic demand, both
actual
and
proposed. Similarly studies of major/minor priority road
junctions have taken account of queue lengths and vehicle delays
particularly when traffic demand exceeds existing capacity.
Formulae will be produced to give new procedures for capacity
prediction and thus lead to improved designs.
ROAD
LIGHTING
The lantern characteristics
and
geometry of installation in street
lighting design have shown many improvements in recent years. The
British Code of Practice for Road Lighting has been built up from
many years of experience,
but
largely relates to the reflection
characteristics of British road surfaces in dry conditions. Wet
conditions however, give streaky reflections and also cause glare so
that
people and objects on the carriageway can become obscure.
Current research aims to establish standards for lighting in
both
dry
and wet conditions whilst also having regard to changes in
reflectivity caused by wear on various types of road surfaces.
MOTORWAYS
Comprehensive surveys of motorway driving speeds have
continued since 1970 and seem to reflect the 50 m.p.h. speed
restriction of early 1974 and subsequent large increases in petrol
prices. Since the end of 1974 there has been no marked tendency
towards increase or decrease of speeds even though petrol prices have
substantially declined in relation to other prices. The table shows the
trends
and
it is thought
that
alonger-term effect may result from
changes in the design and marketing of cars, giving emphasis more to
economy
than
to performance, thus inhibiting areturn to rising
speeds. Traffic volumes on motorways increase more rapidly than on
July 1979 275
other routes and some sections of the network are carrying in excess
of 80,000 vehicles per day.
It
is still true that accidents
and
delays per
vehicle mile travelled are less on motorways than on all purpose
roads
but
the
number
of accidents
and
incidents per mile of
motorway are comparably far higher due to the enormous volume of
traffic carried. Emphasis here is placed on providing drivers with
information and advice to reduce the likelihood of incidents and to
minimise effects when they do occur. More rapid detection of
incidents could give savings in delays and accidents so methods of
automatic
alarm
triggering are being considered. Some
data
is
already available from the Paris Boulevard Peripherique
and
additional understanding of the problems should emerge from
experimental systems installed on the MI motorway in England.
Speeds
ofcars
on Motorwavs M3
and
M4. /973 - /977.
M3 between
junctions
4 and 5. Hampshire
M4
between Junctions 12 and 13. Berkshire
I
@
I I
}d
II
80
'0
CIl
CIl
~-
70
_J:
0"0;
sr=
,,!
60
..
CIl
~
:0
~
•
.5
60 I
~
CIl
UJ:
40
x-
CIl,!!
~'E
J!!o
20
"
.....
CIl
~
CIl
l1. 0
1973
1974
1975
1976
1977
Notes:- ®
Government
recommendation
-
'Don't
exceed 50
mile/h'
®50
mile/h
limit
in force on
motorways
©Petrol shonage at garages
©
Time
of dearest
petrol
relative to
other
prices
276 July /979
Monitoring has shown
that
despite police policies there were 140
complete closures of some part of the motorway system over a two
year period - an extraordinary average of one closure every fivedays.
The disruption caused by such closures is enormous on surrounding
road networks and studies of effects may lead to advice that in some
circumstances the minimum overall delay might result from a
"no
diversion" policy. Research on this subject will allow sensible
management! operational decisions on where or when to close
various motorway sections as a result of incidents against the
alternative of allowing traffic to queue for an hour. Too often instant
decisions are made to divert with disastrous results on surrounding
areas and massive demands on police manpower.
Experiments are continuing with improved signing systems
particularly the pictograms displayed on matrix panels. A
representative sample of drivers seemed to understand the new signs
although it is recognised that publicity would be' required before
introduction. The ultimate three-part system should tell drivers what
to do, the nature of the hazard and its distance ahead. Added to this
signing the broadcasting of traffic information promises to be highly
cost effective. This column has previously devoted considerable
space to this type of message transmission and the practical and
realistic experiment of Carfax recently announced is a welcome step
forwards.
Systems to improve route findings to reduce delays and overall
transport costs are being studied as a result of surveys which
indicated that the most direct route between points is rarely followed.
Improved road signs, more informative maps and comprehensive
electronic aids all
playa
part but there is much work still to be
completed
and
it will be some years before positive
recommendations are made.
So far as roadworks on motorways are concerned Police often
require additional breakdown facilities to cater for potential
problems where traffic flows are restricted. Demands for attention
are naturally higher during the working day and especially at local
peak times. Study of past sites has enabled production of a
mathematical formula, now transcribed intocontoured maps which
make it relatively easy to determine how much expenditure on
improved breakdown facilities can be justified by the expected delay
saving. So far as accidents are concerned the rate increases about
three fold when major road works are in progress. One interesting
fact which has emerged however from the narrow lane operation on
the M6 motorway is
that
the close proximity of opposing vehicles
and lack of a buffer lane does not lift the accident rate above the
norm for a motorway major road works site. (The narrow lane
system operated in late 1976 carryingan average two way daily flow
of 44,500 vehicles providing two lanes of traffic in each direction
011
a
single carriageway for a distance of 6km while road works were in
progress on the other carriageway.
It
seems that capacity of the
July /979 277
narrow lanes did not differ substantially from the capacity of normal
width lanes).
Whilst dealing with road works it is worth noting
that
standards of
signing have been seen to improve in the years following the "Signing
for Safety" exhibition at Crystal Palace in 1972
and
the publication
of
Chapter
8 of the Traffic Signs Manual in 1974.
It
is hoped
that
this
trend will continue
and
lead to more realistic appraisals by drivers of
the hazards they are approaching.
Perhaps it can by now be seen
that
there is a considerable
amount
of work continuing in this country to cope with the ever increasing
traffic volume and potential accident hazard. There are realistic
indications that the work is not all wasted
and
expensive
human
lives
continue to be saved for the benefit of society, atrend we must all
hope will continue. The research also shows that traffic engineers are
becoming more specialised and more reliant on scientists.
It
is vital
that
seniorpolice officers responsiblefor trafficshould keep abreastof
developments and exercise flexibility and sound judgement in
relevant decisions.
278 July 1979
To continue reading
Request your trial