Thames Valley Speed Cameras

An independent report        



All safety devices and policies can have both positive benefits and negative side effects. This page discusses the possible effects of speed cameras on road safety, with reference to the factors that contributed to collisions in 2010.




Collisions      Road traffic accidents that result in fatal, serious or slight injuries, as recorded by Police

KSI               Killed or Seriously Injured. People who suffer fatal or serious injuries in collisions

Speeding      Exceeding the speed limit


Positive benefits of speed cameras


Speed will obviously be a factor in all collisions (no speed equals no collision) and the faster a vehicle is travelling, the longer the stopping distance (if all other factors remain the same). Should a collision occur, a higher initial speed would usually lead to a higher impact speed which would generally lead to greater severities of injuries. By discouraging motorists from speeding, speed cameras should reduce the number of those collisions where speeding was a contributory factor and the size of this problem is known. In 2010, speeding was a factor in around 7.1% of all KSI collisions (contributory factors ksi collisions 2010.xls) but for speed cameras to prevent all collisions that involved speeding would require:


1) - that the speed cameras prevent all vehicles exceeding the speed limit (10.1)

2) - that there are no factors other than speeding in those collisions (10.2)

3) - that the reduction in speed down to the speed limit is sufficient to prevent the collision (10.3)

4) - that speed cameras have no negative side effects (10.4)


10.1 - Speed cameras can be used to prosecute those motorists who exceed speed limits and who can be identified via their vehicle records at the DVLA (Driver and Vehicle Licensing Agency). Therefore speed cameras can only really be effective against this specific group of road users sometimes referred to as MARKs, which is believed to stand for "Motorists Admitting (the offence) via the Registered Keeper" (or all the honest members of the public). Speed cameras don't prevent all MARKs from speeding (millions get caught) and they are unlikely to be effective against all the other groups of motorists (where drivers/riders may not be able to be identified using the DVLA records), such as drivers of stolen cars, the emergency services, criminals, foreign drivers, foreign registered vehicles, joy riders, wealthy people with specialist lawyers or those with incorrectly registered vehicles or illegal, illegible or cloned number plates, etc.


There may be a clue to the relative numbers of these other groups in the success rate in prosecuting motorists. Around 40% of the evidence gathered by speed cameras may not result in an offender being fined or sent on a course (spreadsheet). Some within this 40% may be more likely to both speed and cause a collision, therefore the people posing the greatest risk while speeding may also be the very people that cannot be prosecuted using speed cameras. Unfortunately, contributory factors tables do not identify which collisions were caused by MARKs, and which were caused by all these other groups.

10.2 - Police accident investigations find an average of around 2 factors for each KSI collision so, where speeding was a factor and a speed camera could have reduced the speed, other factors may remain. For example, if a collision that involved speeding also included a driver impaired by alcohol, or defective brakes, or another driver disobeyed a Give Way or Stop sign, or a pedestrian failed to look properly etc, then the collision may still occur despite the presence of a speed camera.


10.3 - The vast majority of KSI collisions occur when motorists are not speeding, so reducing the speed of a vehicle that is about to crash to the speed limit may not be sufficient to prevent the collision or reduce the severity of injuries.


10.4 - Negative side effects of speed cameras


Road safety is complex as millions of people use the road network every day in many different ways. The number and severity of collisions may be influenced by vehicle speeds, weather, traffic volume and type, road type and condition, concentration and skill levels of the road users and a host of other factors. The problem is that each factor will not be independent of the others. Change one and others change.


Furthermore, effects of speed cameras (both positive and negative) may be closely linked to speed limits. If speed limits do not accurately reflect the maximum safe speed for most conditions, are poorly signed, or change frequently, then the effects of speed cameras (particularly negative effects) may be greater.

More collisions as a result of the use of speed cameras may include:


In the following examples, the closest contributory factors for KSI collisions from 2010 are shown so that the relative importance of these factors can be compared with the 1400 (7.1%) KSI collisions that involved speeding.


10.4.1) Motorists may brake suddenly near to speed cameras, or where there are no speed cameras if a motorist suddenly thinks that there may be a speed camera. Even motorists not speeding may brake suddenly if they are not aware of the current speed limit, do not know their exact speed or simply wish to ensure they will not be prosecuted.

906 (4.6%) KSI collisions involved "Sudden braking"


10.4.2) When approaching speed cameras, motorists may be likely to look at their speedometer at about the same time as the vehicle in front might brake. Also, even where there are no speed cameras, motorists attention may be diverted to looking for speed cameras, looking for speed limit signs and monitoring their speedometer much more frequently. This increases the possibility of looking away just as an accident situation develops, such as a child running across the road. Such distractions could lead to motorists taking longer to react to hazards and swerving, or losing control.

4167 (21.2%) KSI collisions involved "Loss of control"

888 (4.5%) KSI collisions involved "Swerved"

440 (2.2%) KSI collisions involved "Distraction in vehicle"

219 (1.1%) KSI collisions involved "Distraction outside vehicle"


10.4.3) Motorists proceed safely by assessing the range of hazards they face and varying their road position, direction and speed etc to ensure they can avoid being involved in a collision. In terms of their speed, this generally means slowing down where there are many hazards and speeding up where there are fewer. Speed cameras might interfere with this natural process by preventing speeding up where there are few hazards (ie where it is safe), especially on those roads where speed limits are set particularly low. This encourages motorists to travel at a slightly more uniform speed close to the speed limit resulting in speeds being lower where otherwise they would be higher (where there are few hazards) and higher where otherwise they might have been lower (where there are many hazards). This could lead to an increase in collisions due to "Travelling too fast for conditions", which is defined as being within the speed limit.

1,780 (9.1%) KSI collisions involved "Travelling too fast for conditions"


Note: There are 2 types of "speed" that Police can assign as a contributory factor to a collision and only 1 of these 2 factors can be assigned to each vehicle involved. If a motorist was travelling above the speed limit at the PPP (Point of Perceived Perception) prior to the collision, Police can assign "Exceeding speed limit" as a contributory factor. If a motorist was "too fast" but below the speed limit, Police can assign "Travelling too fast for conditions". See STATS20 (p89, No 306 and 307).


10.4.4) Motorists attention levels may be closely linked to their perception of speed (ie slow may feel boring). Slower speeds enforced by speed cameras may reduce attention levels leading to failure to notice some other road users.

6,387 (32.5%) KSI collisions involved "Failed to look properly"

10.4.5) People pay greatest attention where danger is perceived. If speed cameras and slower speeds make roads "feel safe" then less care might be taken, particularly by pedestrians and cyclists. Slower cars are also quieter and lack of noise can be such a safety issue that artificial engine noises have been developed for electric cars to alert pedestrians.

2,980 (15.1%) KSI collisions involved "Pedestrian failed to look properly"

10.4.6) Speed cameras can be a very emotive subject. Thames Valley Safer Roads Partnership have told me that their speed camera operators often suffer verbal abuse by angry motorists and some people are so enraged that they have taken to destroying speed cameras. Speed cameras may contribute to an overall deterioration in attitudes to driving with some motorists becoming belligerent, intolerant or even aggressive while driving. Disenfranchised motorists may also become less receptive to important road safety messages.

3,168 (16.1%) KSI collisions involved "Careless, reckless or in a hurry"

884 (4.5%) KSI collisions involved "Aggressive driving"


10.4.7) Slower speeds enforced by speed cameras can mean journeys take longer so increase the risk of tiredness or falling asleep.

371 (1.9%) KSI collisions involved "Fatigue"


10.4.8) Speed cameras take an average of £6.8 million out of the economy every year in Thames Valley therefore speed cameras need to demonstrate a benefit worth this cost, see TVSRP_conversion_rates.xls. As resources are always limited, the cost/benefit of all policies must be judged against the alternatives. For instance, if a Police car costs £50k over 5 years and officers cost £50k pa, then Thames Valley could have 114 more Police officers in 114 more Police cars for the same cost to society as the speed cameras. As we cannot afford both, choices must be made.


10.4.9) Motorcyclists may suffer a particular set of risks from speed cameras. Motorcyclists are far more likely to be killed or injured than vehicle occupants and, when drivers cause collisions with motorcycles, they often say “Sorry Mate, I Didn't See You” (referred to as SMIDSY accidents). It is worth noting that "Failed to look properly" has been the largest contributory factor in KSI collisions by some margin every year. This means that, as well as ensuring they do not cause a collision themselves, motorcyclists have to avoid collisions that drivers might cause. As a result, motorcyclists may require constant adjustment of road position and greater changes in speed than other road users. Eg, it may be less safe for motorcyclists to travel at slower speeds if this results in drivers following too close. It can be more difficult for motorcyclists to monitor traffic behind them (due to the helmet restricting visibility, mirrors being set for a particular riding position, vibration of mirrors, weather, larger blind spots etc) therefore it may sometimes be safer to ride at a higher speed in order to minimise the danger of drivers behind following too close or not paying attention. Also, it may be less safe for motorcyclists to pull away from traffic lights at a slower speed if that results in them being surrounded by other vehicles. It may be safer to use a higher speed to create and maintain a gap to the group of vehicles released by the traffic lights. In this way, motorcyclists can spend more time in clearer sections of road with fewer vehicles that could pose a threat to their safety. Also, where a vehicle approaches from a side road, a motorcyclist on the main road may try to get eye contact, or slow down to ensure the driver stops, or increase their speed in order to pass the junction before the driver reaches it. Also, following slow or erratic drivers can be hazardous as vehicles may then be following the motorcyclist when the driver in front suddenly brakes or turns. A motorcyclist might overtake where it is safe and then select a speed that maintains some distance in order to avoid such dangers.

In short motorcycle safety may require, amongst other things, that motorcyclists be free to select the safest speed for each condition and to constantly adjust their speed. Speed cameras (and lower speed limits) may reduce the ability of motorcyclists to protect themselves in this way resulting in more collisions which are more likely to involve death or serious injury. It may be worth noting that deaths of motorcyclists fell to their lowest level in 1993 (before speed cameras were introduced) and then rose as the speed camera network expanded (see figure 6 from GB road safety).


Note : For contributory factors for all available years from 2005, see Speeding or download contributoryfactors.xls.


Direct influence of speed cameras on collisions:


Direct positive benefits: Apparently there are no examples of collisions that would have been directly prevented by the presence of a speed camera. I have asked for examples of such collisions from the Police, local councils in Thames Valley, the Department for Transport and the Thames Valley Safer Roads Partnership but all have said that none of the collisions they have on record would have been prevented had a speed camera been at the location. Even the collisions that led to a speed camera being deployed would apparently not have been prevented by the speed camera. They say collisions tend to involve several factors and the benefits of speed cameras are in general safety rather than in specific examples.


This is surprising. All these organisations could show (and often have shown) many examples of actual collisions where devices such as seat-belts, ABS brakes, air-bags, collapsible signs, breathalysers, helmets etc have either prevented collisions or injuries, or lack of them led to collisions or injuries. Speed cameras could be unique as the only safety device for which no specific examples can be presented where the device would have provided a benefit.


Direct negative side effects: Accidents have occurred where speed cameras are implicated as a contributing factor. For example, videos shown on the BBC (taken from mobile speed cameras) include 2 accidents which appear to have been triggered by the speed cameras. And there have even been fatalities. A Driver who was "unlikely to have even been speeding" was killed after braking and losing control approaching a gatso speed camera. The death of a pedestrian occurred after a driver may have been distracted by a Gatso speed camera according to the Coroner and the Police accident investigator. A motorcyclist died after he braked and lost control approaching a mobile speed camera.


Video 2 collisions at mobile speed camera sites where motorists braked suddenly and lost control.

Driver who was "unlikely to have even been speeding" died after braking and losing control approaching a speed camera.

Pedestrian died where the coroner suggested the speed camera may have distracted the driver.

Motorcyclist died after he braked and lost control approaching a mobile speed camera.


This is not a complete list of examples of direct negative side effects. I would have presented examples of direct positive benefits but I can't find any and the authorities say there aren't any.


For more information on accident investigation, and specifically exceeding the speed limit as a factor, see speeding.