Speed estimation

Speed estimation variables

In an earlier post, we wrote about the different types of speed measurement used in British Columbia. We told you that we would expand on some of the studies and research that has been done into the factors that can contribute to inaccurate speed estimations. A surprising amount of research has been done in this area, and BC Driving Lawyers maintain an extensive library of documents pertaining to potential errors in speed estimation.

Speed is calculated using simple math. The distance covered divided by the time taken to cover the distance will produce a speed estimate. However, time is measured in seconds in this equation and a small error in time can result in a large difference in speed. Any object traveling directly at or away from the observer will appear to be moving faster. This increases over distance such that at great distances a vehicle that is coming directly forward may appear stationary. Consequently, it is difficult for an individual who is judging speed to do so when the vehicle estimated is traveling immediately in front of the person making the estimate. The same holds true for vehicles traveling directly toward the person estimating speed.

[pullquote]Any object traveling directly at or away from the observer will appear to be moving faster.[/pullquote]

A Spanish study, conducted in 2009, analysed the speed estimation of a passenger in a vehicle in different scenarios. It is clear that speed estimation can be influenced by the fact that the person making the estimate is in a moving vehicle. The study found that speed awareness relied on a balance of objective and subjective factors. Most individuals were able to come up with a reasonably accurate estimate where they had the ability to inspect the speedometer and compare it to visual and auditory clues around them. However, as the demands on the subject increased, the speed estimation became increasingly subjective. This was attributed to the fact that the more attention an individual had to pay to the conditions surrounding them, the more the individual relied on factors other than an objective measurement (like the speedometer) to make a speed estimation.

This study was conducted on both open road and a closed track. Unsurprisingly, individuals on a closed track were subject to fewer distractions. The result of this is that their speed estimations were significantly more accurate than those made on open road. Error rates did not tend to change as speed levels increased, but error rates did increase depending on the type of road traveled. For example, on highway the error rates were higher than on suburban streets. The authors of the study suggested that the presence of parallel traffic flow, which is a notable interference in the accuracy of speed estimation, contributed to this difference. They noted that participants in the study relied more strongly on cars traveling in the same direction than on cars traveling in the opposite direction to inform their speed estimation.

Age has often been attributed as a variable that can impact speed estimations. In 1991, a study was conducted comparing the speed estimates of young people to those of more experienced drivers. The authors of the study wanted to determine whether there were any significant changes in the ability to estimate speed throughout a person’s lifetime.

The study determined that young drivers are well able to determine speed accurately, based on estimation. While there were errors, the overall best estimates of speed were made at higher speeds. Young drivers tended to overestimate low speeds and underestimate high speeds. The errors detected increased as visual cues or where the ability of drivers to see was reduced.

[pullquote]Older drivers were not as readily able to detect changes in motion as younger drivers.[/pullquote]

Curiously, the study found that older drivers were not as readily able to detect changes in motion as younger drivers. Statistically, they have a larger percentage of accidents that are explained by distraction and poor estimation of distance and speed and the rate of error in speed estimation was greater as age increased. Elderly individuals appeared to judge vehicles as traveling more quickly than young people. This occurred even where the vehicle was traveling at a low speed of approximately 25 km/hr. So although one would expect a younger individual to be less capable of producing a reliable speed estimate, the study concluded that with age people became more susceptible to errors in making speed estimation.

Other studies found errors in speed estimation that were relatively common. For example, on a hill or a grade, speed estimation was less accurate. The same holds true for speed estimation made relying on mirrors. This means that where a vehicle is approaching from behind, the speed estimation will be less accurate than if the vehicle is oncoming or approaching from an angle. Because the studies concluded overall that the increased number of visual clues available to an individual increased the likelihood of an accurate speed estimation, it is also unsurprising that speed estimation is less accurate at night than it is in the daytime.

These and hundreds of other errors make it difficult for police officers to produce reliable speed estimations. If your violation ticket was based on an estimate of speed, a BC Driving Lawyer can help you dispute the ticket and keep the points from your driving record.

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