If both parties made mistakes in a road accident, who is legally liable?

Why

The governing rule for vehicular accidents in Philippine civil law is found in Article 2176 of the Civil Code: whoever by act or omission causes damage to another through fault or negligence is obliged to pay for the damage done. The foundational test of negligence was formulated by the Supreme Court in the landmark case of Picart v. Smith (G.R. No. L-12219, 1918): would a prudent person (the 'discreet paterfamilias' of Roman law), situated in the actor's position, have foreseen harm as sufficiently probable to warrant foregoing the conduct or guarding against its consequences? If so, ignoring that reasonable prevision constitutes actionable negligence.

When both parties have committed acts of negligence at different points in time, courts apply the Doctrine of Last Clear Chance. If one party negligently places themselves in a position of peril (such as riding on the incorrect side of a bridge), but the other driver perceives or ought to have perceived the predicament while still having sufficient time, space, and control to avoid the impact, the law fixes full responsibility on the latter driver. Because the approaching driver possessed the last clear opportunity to prevent the harm, their failure to slow down or veer away constitutes the proximate and determining cause.

While Article 2179 of the Civil Code provides that contributory negligence on the part of the plaintiff mitigates the damages to be awarded, that principle applies only when the negligent acts of both parties are concurrent or contemporaneous. Where an appreciable interval elapses and one party has the final chance to avoid the tragedy, the Doctrine of Last Clear Chance supersedes contributory negligence, entitling the injured party to recover for medical expenses, property repairs, and legal damages.