In the event of a dispute over liability for a motor vehicle accident, in many cases the deciding factor is likely to be the evidence of a third party witness. A third party witness is a neutral witness that has no loyalty to either side of a dispute. In a situation where you have two drivers each giving different accounts of an accident, the courts are likely to rely heavily on the testimony of a third party witness. In the courts eyes, these witnesses have no motivation not to tell the truth, and their evidence is given a lot of weight.
Witnesses are also likely to disappear. People change phone numbers and e-mail addresses or simply become more unwilling to provide testimony as time passes. A good lawyer will be able to hire investigators to get formalized witness statements early.
The importance of witnesses was illustrated in this Supreme Court of British Columbia case:
http://www.canlii.org/en/bc/bcpc/doc/2015/2015bcpc296/2015bcpc296.pdf
Here, a driver claimed that he had been the victim of a hit and run. ICBC made the allegation that the driver was making a fraudulent statement and had instead been injured in a single vehicle accident, which he had caused. ICBC brought this matter before the police for the purpose of a criminal conviction. The driver was ultimately convicted criminally, and a main piece of evidence the courts relied on was the testimony of a nearby salt truck driver, who stated that he had not seen another driver in the area around the time of the car accident.
