The challenge facing any traffic accident prevention program is that 
crashes are very infrequent events. The average motorist experiences one 
culpable (at fault) crash about once a decade, and one crash involving a 
casualty (injury or death) every three decades 
(http://www.vtpi.org/tca/tca0503.pdf). Even motorists categorized as high 
risk go most years without a crash. In addition, since safe driving is 
considered a skill, most drivers consider themselves "better than average" 
as a matter of pride. As a result, motorists generally consider safety 
strategies such as traffic speed reduction rules to be unnecessary.

There has always been a debate over traffic speed restrictions, with some 
people claiming they are excessive and unnecessary, particularly on modern, 
grade-separated highways. However, there is good evidence that not only do 
speed reductions reduce crash frequency and severity, urban area speed 
control is also important for increasing non-motorized travel and reducing 
traffic noise, and therefore urban livability. For information see the 
"Speed Reductions" (http://www.vtpi.org/tdm/tdm105.htm), "Traffic Calming" 
(http://www.vtpi.org/tdm/tdm4.htm) and "Safety Evaluation" 
(http://www.vtpi.org/tdm/tdm58.htm) chapters of our Online TDM Encyclopedia.


Best wishes,
-Todd Litman


At 05:26 PM 12/8/2004 +0000, Richard Allsop wrote:
>I have no wish to become involved with "The Progress Report", but I think 
>those who have been circulated the US Professor's article should have 
>chance to see this GB Professor's view of the matter
>
>SPEED MANAGEMENT:  WHY, HOW. AND THE ROLE OF SPEED LIMITS AND THEIR 
>ENFORCEMENT?
>(Text that forms part of other contributions by the author on this topic; 
>December 2004)
>
>Richard E Allsop, Centre for Transport Studies, University College London
>
>1          Why speed management and why this usually means moderating speed
>
>Speed brings great benefits in the form of shorter travel times for people 
>and goods (and sometimes enhancement of the experience of travel) at 
>substantial cost, especially in terms of accidental death, injury and damage.
>
>We all share in the benefits from speed (even those who rarely or never 
>use a private vehicle) and we all bear some share of the costs. The 
>benefits from speed are probably neither more nor less fairly shared 
>across society than many other kinds of welfare - but the sharing of the 
>costs in terms of accidents is unfair in two distinctive ways:
>·                    many of the costs are borne by those who do not 
>benefit most directly from speed, notably those who walk and cycle most; and
>·                    massively disproportionate costs are borne by the 
>minority who are killed or seriously injured in accidents and by their 
>close associates.
>
>Prevailing speeds are determined by the choices made by drivers and riders 
>on each stretch of road as they find it.   They get much of the benefit of 
>higher speed immediately for themselves and their associates in terms of 
>earlier arrival, and possibly the pleasure of going faster.   They do bear 
>some of the cost themselves (mainly increased running costs and risk to 
>themselves and their associates) but they are known to underperceive these 
>costs.  They do not themselves bear any of the human costs of accidents to 
>others, or much of the resulting damage to the environment.   For these 
>reasons, there is a tendency inherent in the road traffic system for all 
>of us to go faster than is good for ourselves or society.
>
>All this means that responsible government of any party must seek to 
>influence speed, and in many respects to moderate it, and this means 
>influencing the choices not just of a less responsible minority, but of 
>all of us as users of motor vehicles, even those of us who may be tempted 
>to think of ourselves as the most responsible, even altruistic, of 
>citizens.   We are all liable to drive or ride at speeds inappropriate to 
>the circumstances, and the ultimate aim of speed management is to achieve 
>appropriate speeds by all drivers and riders in all circumstances.
>
>2          How speed can be managed
>
>Technology is already beginning to offer the long term prospect of 
>achieving this ultimate aim of speed management, without unnecessary 
>restriction upon the more capable drivers or riders of the best equipped 
>vehicles, by means of an intelligent on-board speed regulator.   This 
>would limit the drivers or riders choice of speed at any instant by 
>imposing an appropriate maximum in accordance with the prevailing local 
>road environment, the capability and condition of the vehicle, and the 
>current level of performance of the driver or rider.   But this is looking 
>ahead many years, and even all but the first steps towards it are some 
>years away.
>
>In the meantime, the main ways of managing speed are to influence 
>driversand ridersindividual choices by:
>·                    education, training and public information education 
>about the factors that determine what speed is appropriate, training in 
>judging appropriate speed while driving or riding and controlling the 
>vehicle to achieve that speed, and public information to inform education 
>and maintain awareness in the educated;
>·                    adapting the layout and appearance of the roads so 
>that on each length of road the speed that looks and feels appropriate to 
>most drivers and riders is indeed appropriate in the circumstances;
>                      adapting the capability of vehicles so that speeds 
> beyond the range that is acceptable on public roads are no longer 
> available to people driving or riding there; and
>·                    using traffic law to regulate driversand riderschoice 
>of speed for the time being mainly by posted speed limits that apply at 
>all times to the relevant stretches of road (though limits that differ 
>according to time of day or traffic conditions are beginning to be used).
>
>The rest of this contribution is concerned with the fourth the role of 
>speed limits and their enforcement in speed management.
>
>3          The role of speed limits and their enforcement
>
>Imposing a speed limit on a stretch of road does not address the aim of 
>achieving appropriate speeds directly.   It does so indirectly by setting 
>a maximum permitted speed, in the reasonable expectation that speeds 
>chosen having regard to the imposed limit are more likely to be 
>appropriate than would be the case if the limit were higher (or if there 
>were no limit at all, as was the case on many roads in Britain until 
>1965).   Where there is a speed limit, speed higher than the limit is 
>described as excess speed, and it is driving with excess speed that 
>constitutes an offence.   Driving with inappropriate speed within the 
>limit constitutes an offence only if the speed is so inappropriate as to 
>amount to careless, inconsiderate or dangerous driving within the meaning 
>of the Road Traffic Act 1991.
>
>The relationship between excess speed, as defined and addressed by 
>imposing a speed limit, and inappropriate speed, which speed management 
>ultimately seeks to address, may be illustrated by the following table, 
>which shows the resulting four possibilities in respect of the speed 
>chosen by a driver or rider in given circumstances.
>
>Speed within the limit
>Appropriate speed       No problem
>Inappropriate speed     Not addressed by the limit
>
>Speed above the limit (excess speed)
>Appropriate speed       Law nevertheless requires speed to be reduced for 
>the common good
>Inappropriate speed     Addressed by the limit to the extent that bringing 
>speed below limit makes it less inappropriate
>
>A speed limit could be a completely effective means of speed management 
>without requiring anyone to travel more slowly than is appropriate in the 
>circumstances only if all speeds fell in the upper left or lower right 
>hand cells of the table and all drivers and riders complied with the 
>limit.   This will clearly never be the case, but extent of approximation 
>to it may be a useful criterion in judging how reasonable an existing or 
>proposed limit is for a given stretch of road and its traffic.   In other 
>words, a reasonable limit is one such that speeds below it are appropriate 
>and speeds much above it are inappropriate for most drivers and riders in 
>most circumstances, so that not too many are denied the right to travel at 
>higher but nevertheless appropriate speeds, and not too many speeds within 
>the limit are nevertheless inappropriate though there will always be some 
>of these, notably when weather or other conditions call for greater 
>caution than is usual for that stretch of road.
>
>Clearly then, speed limits cannot address all kinds of inappropriate 
>speed, but this fact is no reason for failing to use them to full effect 
>to deal with the kinds of inappropriate speed that they do address namely 
>speeds that are usually inappropriately high for the stretch of road concerned.
>
>If speed limits are to be effective and respect for them as traffic law is 
>to be maintained (or, where it has been lost, regained), they need either 
>to be largely self-enforcing (like 20 miles/h limits made so by road 
>layout), or perceived to be enforced.
>
>According to the principles set out in the North Report (Department of 
>Transport and The Home Office 1988), enforcement should be 
>proportionate:  it should bear hard upon the blatantly irresponsible 
>offender, whilst responding to occasional infringements by basically 
>law-abiding drivers with penalties that they are able to see as sharp but 
>justified reminders keep their driving up to the mark.


Sincerely,
Todd Litman, Director
Victoria Transport Policy Institute
"Efficiency - Equity - Clarity"
1250 Rudlin Street
Victoria, BC, V8V 3R7, Canada
Phone & Fax: 250-360-1560
Email: [log in to unmask]
Website: http://www.vtpi.org