Domeney v Rees & Ors

Expert evidence in a road-traffic claim should be permitted only where it is reasonably required to resolve the proceedings. Experts must provide scientific or technical assistance, not determine factual issues that are for the trial judge, such as the speed of a vehicle derived principally from eyewitness evidence.

Counterfactual accident scenarios requiring successive assumptions about speed, collision dynamics and hypothetical injuries may be too speculative to assist the court. They may also impose disproportionate cost and create spurious precision in an assessment of contributory negligence that is necessarily broad-brush. The distinction between causation and causative potency does not require such evidence where both issues depend on the same speculative exercise.

The claimant brought a fatal road-traffic claim against the driver of a Ford Fiesta and his insurer. Primary liability had been conceded, and the defendants sought permission to rely on a further accident reconstruction expert and an A&E consultant in connection with a proposed preliminary issue concerning contributory negligence.

The proposed evidence was intended to address the deceased’s speed, whether a slower speed might have avoided the collision, and whether alternative collision scenarios would have reduced the injuries or avoided death. The court also considered whether an existing accident reconstruction report should be admitted.

1. Permission for further expert evidence refused. The test under Part 35 of the CPR was whether the evidence was reasonably required to resolve the proceedings. That test was not satisfied.
2. Two existing accident reconstruction experts had stated unequivocally that the motorcycle’s speed could not be reliably calculated. Their reasons were cogent. The court would therefore have to determine speed from the lay evidence. In accordance with the principle explained in Liddell v Middleton [1996] PIQR P36, an expert may provide scientific criteria and assistance, but may not determine factual issues for the trial judge by interpreting eyewitness evidence.
3. The proposed alternative scenarios were highly speculative. They would require experts to construct hypothetical collision dynamics and then ask medical experts to predict hypothetical injuries. Such evidence would not materially assist the court and would add substantial cost and trial time.
4. The assessment of contributory negligence requires an evaluation of blameworthiness and causative potency. It is an essentially impressionistic and broad-brush exercise. The approach proposed was inconsistent with the warning against prolonged or intensive inquiries into fine degrees of contributory negligence in Stanton v Collinson [2010] EWCA Civ 81. The distinction between causation and causative potency did not alter the conclusion.
5. The existing report of Mr Loat was admitted, together with the police reports, because it contained data and observations already available to the parties and its admission caused no unfairness. Permission for a newly instructed accident reconstruction expert and an A&E consultant remained refused.