Memorandum by David T Silcock (RTS 12)
ROAD TRAFFIC SPEED
David Silcock has over 30 years experience in
transport consultancy and research. He has been active in road
safety research since the 1980's, when he was Deputy Director
of the Transport Operations Research Group at the University of
Newcastle upon Tyne. David Silcock has led many research projects
in the field of road safety, for organisations such as the DTLR
and the former DETR, the AA Foundation for Road Safety Research,
DFID, the former Scottish Office, and international bodies such
as the World Bank. He is currently one of eight international
advisers to the Global Road Safety Partnership and is a member
of PACTS Road User Behaviour Working Party.
Of particular relevance to this inquiry is the
research work led by Mr Silcock for the AA Foundation for Road
Safety Researchpublished under the title What Limits Speed?
This paper draws heavily on that work. Also, he is currently project
director of a research contract for the DTLR which is investigating
Rural Road Hierarchies for Speed Management Purposes (A Progress
Report on this subject was placed in the House library by the
Minister at the end of November).
This research is also examining the possibility of a simplified
method for making speed limit orders, and the potential use of
village signs to designate speed limits in villages.
This memorandum accepts that there is a strong
relationship between speed and both the number and severity of
crashes. It is assumed that the Committee will take evidence from
othersfor example from TRLwho can substantiate this
The challenge facing road safety professionals
is expressed in the term "Speed Management". We must
take a system-wide view, encompassing roads, vehicles and road
users, and manage traffic speeds in this system in order to reduce
the numbers of casualties without imposing unreasonable and uneconomic
constraints on mobility. Speed management in these terms is seen
as a major contributor to the achievement of the national casualty
reduction targets set out in the government's road safety strategy
Tomorrow's RoadsSafer for Everyone.
1. ILLEGAL AND
1.1 Many road safety professionals separate
speeding into "excess speed", which is above the prevailing
limit and therefore illegal, and "inappropriate speed"
for the prevailing circumstances. To the road safety professional
appropriate speeds are most likely to be below the legal limit,
but ordinary drivers reveal by their driving behaviour that the
common view of what is an appropriate speed to them is often above
the legal limit. This difference of views is fundamental to the
issue of speed management. I will return to what influences a
driver's choice of speed.
1.2 There is a presumption in the notion
of "appropriate speed" that it can be determined scientifically
and, once determined, it can be communicated to drivers who will
respond. It is probable that the appropriate speed will vary by
time of day, traffic conditions, weather, and even vehicle and/or
driver abilities. Pursuing this to the limit (!) implies an extensive
infrastructure to monitor condition, to inform drivers and to
influence, or control, their behaviour. In effect this implies
variable, advisory speed limits. This is not practicable in the
foreseeable future due to the absence of the necessary infrastructure
and our inability rigorously to determine optimum appropriate
1.3 Further, even if we were able to define
a wide range of preferred speeds on a rigorous basis, it is impractical
to expect drivers frequently to change speed. We must therefore
be pragmatic and fall back on an approach to managing speeds which,
whilst based on the available evidence about the relationship
between speed and safety, is straightforward and acceptable to
road users and to those who design and manage the road network.
This would include all aspects of the systemthe road, road
users and vehicles. Within this is a general presumption that
reducing speeds will provide road safety benefits.
2. WHY DO
2.1 Our research for the AA Foundation found
that 85 per cent of respondents to a household survey (of 1,000
households) admit that they "find themselves speeding on
occasion". In a further strand of the research, all but five
of 243 drivers who drove a pre-determined route whilst being filmed
from within the car exceeded the prevailing limit at least once
during their one-hour drive.
2.2 In broad terms drivers said they choose
a speed at which to drive because "it feels right".
Drivers appear to set themselves an internal speed limit which,
in their judgement, is appropriate for them under the prevailing
conditions. This internal limit is often, but not always, above
the prevailing legal limit. Our video-drives and the subsequent
interviews of drivers using the video tape as a prompt, revealed
that speeding was often a conscious decision. Accidental speeding
as relatively rare.
2.3 Drivers acknowledge speeding as illegal,
but it is justified on a number of grounds:
In a hurry (eg to collect a child
Being "forced" to speed
The limit is wrongly set for this
location (based on similar roads with a higher limit);
My modern car can stop more quickly
than those on the roads at the time the limits were set, therefore
my speeding is safe;
The same speed limit should not apply
at all times (eg empty roads, late at night);
The limit does not apply to me because
I'm an above average driver;
My speeding is acceptable because
its not a lot over the limit and others abuse it more flagrantly.
2.4 But not all speeding is acceptable in
the public mind. There is a dichotomy between "my" speeding,
for which there are good reasons, and "others" speeding,
which is not always accepted. Our surveys revealed a number of
factors which have an influence on a speed "feeling right"
to an individual:
Self-image as a driver.
Presence of passengers.
Perceived risk of detection and prosecution.
2.5 In common with many surveys, we found
that the great majority of drivers rated their driving abilities
as "average or above". The speeding driver is characterised
as a "boy racer" or the "company car driver"and
few admit to being in either category.
2.6 There seemed little doubt from our surveys
that modern vehicles encourage speeding, not necessarily by the
direct promotion of power and the pleasure of speed, but in a
more passive way by insulating the driver from the effects of
speed. The absence of noise, vibration and "wind in the hair"
are obvious features; comfort, internal protection and sound systems
were also cited by drivers as features which encourage speeding.
2.7 It is clear from our surveys that drivers
generally make their own assessments of the speed at which they
will drive, irrespective of the speed limit. We found that, as
a broad generalisation, the sections of road with the highest
proportion of speeding drivers were those with 30 or 40 miles/h
limits, which were also wide, straight and with little frontage
activity. Dual carriageways with 30 or 40 miles/h speed limits
were particularly susceptible to speeding.
2.8 The fact that speeding is commonplace
reinforces the views expressed in our surveys that there is little
fear of detection or prosecution. There was also a widespread
belief that the police allow a fair degree of tolerance on top
of the legal limit. Fines for speeding were considered low, and
thus ineffective. For some groups other forms of penalty were
considered to be potentially more effective, for example community
service or compulsory re-training.
3. HOW COULD
3.1 Although the majority of our survey
respondents accepted the existing speed limits, confusion prevailed
about their application. Other than 30 miles/h and 70 miles/h
they are not well understood and there is a widespread public
view that they are not consistently applied. Intermediate speed
limits should be reviewed, with firm guidance provided about their
3.2 The absence of any apparent reason for
a specific speed limit emerged in our surveys for the AA Foundation
as one factor leading to abuse. There are examples of advisory
speed limits and variable message signs which display reasons
for the limit, but the current policy of speed limit signs being
used without any other information should change. Drivers should
be told why the speed limit is being imposed.
3.3 The road hierarchy should be revised
to provide a more consistent relationship between the functions
of a road and a speed management hierarchy. A possible template
for this is shown below, based on our current work for DTLR, a
progress report on which is available in the Commons library.
The aim of this hierarchy is to provide a framework within which
a consistent approach to speed management can be adopted by those
responsible for the road network. This should provide more consistent
messages to road users about the speeds which they should not
expect to exceed.
Through traffic and
|70 mph||Dual carriageways only
|60 mph||High quality single carriageways
|50 mph||Poor quality single carriageways
||Roads with open aspect and limited presence of vulnerable users
|40 mph||Exceptional town or village with wide roads and good provision for vulnerable users
||Poor quality roads with frequent access points and junctions
||Between villages and open aspect roads
|30 mph||Towns and villages
||Towns and villages||Villages with adequate footways. Poor quality roads with vulnerable users
||Exceptional use in villages with restricted layouts and many vulnerable users
||Quiet lanes. Villages without footways and narrow roads
3.4 Intelligent Speed Adaptation (ISA) is promoted by
some as the long term solution to the speeding driver. It offers
much promise as a means of providing information to drivers, for
example it could ultimately remove the need for roadside signs
to tell the driver what the speed limit is at any given location.
As a potential information source it was well received in our
surveys. However, there was marked reluctance to control being
taken away from the driver. There are legal issues of responsibility
here that require careful consideration.
3.5 The presence of other vehicles was the most often
cited factor causing drivers to slow down, and the third most
frequently cited factor causing drivers to speed up"the
car ahead pulled away, therefore I could also speed up".
Comprehensive traffic management, in its broadest sense, may therefore
have a role to play in managing speeds as traffic volumes grow.
The M25 variable speed limit signs are an example of how this
may be done on major roads.
3.6 From our surveys, the thought of having to undergo
compulsory retraining seemed to be a particularly effective deterrent
to those drivers with the highest opinion of their own driving
abilities. As driver improvement schemes appear to have a positive
impact on the attitudes and behaviour of the participants, they
may be useful in changing the behaviour of speeding drivers.
4. POLICIES AND
4.1 A strategic approach is needed. A balance must be
struck between the needs and expectations of all road users in
terms of safety and mobility. Highway authorities should be encouraged
to develop speed management plans as part of their Local Transport
Plans and funding should be linked to the acceptability of the
speed management plan.
4.2 Government's guidelines on setting speed limits should
be reviewed in the light of proposals for revising road hierarchies.
Local Transport Plan funding should be dependent on the Authority's
speed management plan revising its road hierarchy in accordance
with the guidelines.
4.3 Speed management plans should contain a systematic
review and updating of current speed limits and proposals for
changes in accordance with the new guidelines.
4.4 Speed limit signs should present a message to road
users, giving a reason for the limitparticularly where
this may not be obvious to drivers.
4.5 Further research and development of Intelligent Speed
Adaptation should be supported. A national digital map showing
speed limits and their locations offers an alternative to a plethora
of signs and markings. Ultimately ISA can provide a means of external
control which could be used to prevent excessive speeding.
4.6 Efforts must continue to communicate the risks of
speeding and to foster a responsible attitude to other road users.
Too many drivers do not accept their own speeding as increasing
risk to themselves, or others, and disassociate themselves from
current target groups for publicity campaigns.
4.7 Changing attitudes will take time, and must address
today's drivers through enforcement and penalties, and future
drivers through driver training and educational programmes for
4.8 The proposed Hazard Perception tests, to be incorporated
into the driver testing procedure, should include speed-related
4.9 Driver improvement schemes should be encouraged,
and if current research into their effectiveness supports their
continued use, they should become a court disposal. Course content
should be reviewed to ensure that the risks which result from
speeding are fully addressed and that they focus on changing drivers'
attitudes and behaviours.
David T Silcock
Babtie Group Ltd
Silcock, D, Smith, K, Knox, D and Beuret, K (2000). What Limits
Speeds? Factors that affect how fast we drive. AA Foundation
for Road Safety Research. Back
Silcock, D T, Turner, B M, & Walker, RT (2001). Development
of a rural road hierarchy for speed management-Progress Report.
Babtie Ross Silcock. Back