The concepts of causative potency and the parties’ relative blameworthiness are becoming more prominent in the assessment of contributory negligence in complex road traffic accident claims.
The analysis undertaken by a court in such an assessment will often take the form of the following questions:
1) Whose conduct is more causatively potent in the circumstances?
2) Who is more blameworthy in the circumstances?
The answers to those questions are said to allow the Courts not only to determine the apportionment of damages in a given case but also, to reach a fair and equitable outcome.
Whilst the questions posed appear to be rather simplistic, the task of the apportionment appears to be far from straightforward and is very much interlinked with the circumstances of each case. This has been well-illustrated by the Supreme Court in the case of Jackson v Murray  UKSC 5, where the Court described the apportionment as “somewhat rough and ready exercise” indicating that “it is not possible for a court to arrive at an apportionment which is demonstrably correct” and that the task can legitimately produce a variety of possible answers.
Road users requiring extra care
Paragraph 204 of the Highway Code describes “pedestrians, cyclists, motorcyclists and horse riders” as the most vulnerable road users. What follows, when a vulnerable road user is involved in an accident with a car, at the outset, the balance of causative potency is likely to be against the party driving a car as a result of a car being described as “a potentially dangerous weapon”. This can be seen in the recent case of Hernandez v Acar  EWHC 72 (QB) where despite the balance of blameworthiness being held against the Claimant for driving at excessive speed, the fact that a motorcyclist can be regarded as a vulnerable road user (who may potentially sustain more significant injuries in a collision with a car) tipped the balance in the Claimant’s favour, resulting in a contributory negligence finding of 60/40 in the Claimant’s favour.
It should be mentioned, however, that whilst the driver of a car is expected to maintain a greater standard of care whilst on the road, a court will also closely scrutinise the conduct of the vulnerable road user and if their conduct can be described as being more causatively potent than that of a driver, this will be reflected in the apportionment of damages. This can be exemplified by the case of Ehrari v Curry  EWCA Civ 120 where the conduct of a pedestrian stepping blindly into the path of a vehicle driving at a reasonable speed was regarded as being “the more direct and immediate cause” of the injuries sustained, simultaneously tipping the balance of causative potency and blameworthiness against the pedestrian. The element of the Claimant’s contributory negligence was assessed here at 70%.
Causative potency and blameworthiness outside the road traffic law
Despite the test of causative potency and the parties’ respective blameworthiness being predominantly used in road traffic accidents, some Scottish courts have applied the test outside the road traffic law.
In Lowe v Cairnstar Limited 2020 S.L.T. (Sh Ct) 151, the All-Scotland Personal Injury Sheriff Court applied the test in an occupiers’ liability claim concerning the pursuer slipping and falling on a tiled floor in a nightclub. In the judgment, Sheriff Braid assessed the pursuer’s contributory negligence at 25% ,simultaneously highlighting that “greater share of blame must attach to the defenders, as their failure [to comply with their duty under section 2 of the Occupiers Liability (Scotland) Act 1960] had a greater causative potency” that than of the pursuer’s conduct.
Similarly, in the case of Francis Hughes & others v Turning Point Scotland  CSOH 42, the Outer House assessed the causative potency and blameworthiness of both parties in the context of the events leading to the pursuer’s death. Here, the Court concluded that in the event of a judgment passing against the defenders, the more potent and causative factor of the pursuer’s death was his alcoholism as opposed to the defenders’ failure to take reasonable care in their dealings and treatment of the pursuer. Accordingly, the pursuer’s damages would have been reduced by 60%.