Road collisions: How reliable are witnesses?
The bedrock of our judicial process is the honesty of witnesses. Our recent attendance at a road crash investigation event – where we were able to witness a number of ‘real’ collisions’ – led to some interesting conversations with police crash investigators about the reliability of witnesses. These experts, trained and equipped with precision scanning equipment, frequently reach conclusions that are far removed from the accounts provided for them by witnesses at the scene of a crash. Trouble is, police officers are generally called to a crash once it has happened. They seldom have the opportunity to be on the spot as metal collides with metal. Understanding the science is important, but to see it actually happen is a useful endorsement of the mathematical formulae and equations they rely on. Hence the value of the exercise on the runway where they have had the chance to see the what happens when, for example, one vehicle strikes another at 45mph. Our ability to judge the rate of speed of a vehicle depends on the circumstances during which the observation is made and the vantage point of the observer. A vehicle passing by a pedestrian in close proximity, for example, will tend to generate an impression of higher than actual speed. So, are witness statements, oral or written, reliable? How many times have three witnesses given three different versions of how a single collision occurred? Is someone telling lies or could they perhaps merely be mistaken? Does it sound like these people must have witnessed three different accidents?
Some witnesses try to be too helpful. They will tell you what they think they saw, not what actually happened. Others tell officers what they think they want to hear.
According to reports in the American press, “Those who study memory are becoming increasing unwilling to trust it.” Researcher Henry Roediger, at the American Psychological Association, said that experiments with college students at Rice University in Houston indicate that it’s quite easy to introduce false memories. “People confidently remember events that never happened to them,” he said.
Other experts warn that terrifying incidents are particularly susceptible to memory mistakes because the horror and confusion interferes with the memory process.
That’s why, in the event of a serious collision, the forensic evaluation is typically based on the science – the undisputed physical evidence – and is therefore generally more reliable than witness versions of events. Physical evidence can be helpful in determining which witness statements are useful and which are misleading. An experienced crash investigator can normally sort out which reported information is reliable, and add this to the information available from physical evidence to complete a proper reconstruction of events – the best way of working out what really happened.