In Preparing and Presenting Expert Testimony, traffic engineer and accident reconstruction expert witness Lawrence Levine writes:
All too often an expert walks into court and it is discovered through questioning that he or she only saw the site the day before trial; that he or she only saw photographs provided by the attorney and did not see several others; or that he or she did not bring their notes to court. To a jury or a judge who is trying to determine the merits of a case as well as the reliability and truthfulness of the witness before them, any one of these questions can totally undermine the expert’s credibility. Once credibility is lost, generally the tryer of fact and jury members discounts the witness.
Gathering of Information The investigating traffic engineer must determine exactly which aspects of the case are within his realm of responsibility if he is to be a fact witness. Fact witnesses generally are not asked for opinions. For the traffic engineer who will appear as an expert witness, opinions will be required. Therefore, it is expected that they will have familiarized themselves with the following:
1. Police measurements, photographs, investigation and reconstruction;
2. Any other investigation or reconstruction, measurements and photographs;
3. The issues of the case, including all the pleading documents and expert witness exchanges;