Select Committee on Transport, Local Government and the Regions Appendices to the Minutes of Evidence

Memorandum by David T Silcock (RTS 12)


  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 Research—published under the title What Limits Speed?[23] 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).[24] 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 others—for example from TRL—who can substantiate this assumption.

  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 Roads—Safer for Everyone.


  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 speeds.

  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 system—the road, road users and vehicles. Within this is a general presumption that reducing speeds will provide road safety benefits.


  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:

    —  Unintentional;

    —  In a hurry (eg to collect a child at school);

    —  Being "forced" to speed (by tailgating);

    —  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.

    —  The vehicle.

    —  The road environment.

    —  Cultural factors.

    —  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.


  3.1  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 use.

  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.

Tier 1
Through traffic and
Tier 2
Mixed use
Tier 3
Road class
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
20 mph
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.


  4.1  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 limit—particularly 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 schoolchildren.

  4.8  The proposed Hazard Perception tests, to be incorporated into the driver testing procedure, should include speed-related hazards.

  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

Divisional Director

Babtie Group Ltd

January 2002

23   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

24   Silcock, D T, Turner, B M, & Walker, RT (2001). Development of a rural road hierarchy for speed management-Progress Report. Babtie Ross Silcock. Back

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