Location: One-way, single-lane road
Vehicle order:
① Leading passenger car
② Defendant A (vehicle that sounded the horn)
③ Porter II truck
④ Bongo III refrigerated truck
1. Accident Details
A sounded the horn to signal an intention to overtake.
The driver of the leading car was startled and braked suddenly.
The following Porter II truck collided with A’s vehicle (first collision).
The impact caused A’s vehicle to hit the car in front again.
The Bongo III behind then crashed into the Porter II (second collision).
In total, a four-vehicle chain-reaction collision occurred.
2. Parties’ Arguments
Insurer’s side
A’s use of the horn was the direct cause of the accident.
The horn was used unnecessarily and inappropriately, and triggered the leading car’s sudden stop.
The rear-end collisions that followed were also connected to the first accident.
Therefore, A’s share of fault should be significant.
Driver of the horn-sounding vehicle
The horn was simply to indicate the intent to overtake and was within normal, lawful driving conduct.
The real problem was the leading driver’s overreaction and sudden braking.
The chain collisions were due to the following vehicles failing to keep a safe distance, so A’s responsibility should be limited.
Other drivers
They acknowledged that A’s horn caused the leading car’s sudden stop.
However, they argued that the chain collisions were also caused by unsafe following distances and inadequate response to the sudden stop, so fault should be shared.
3. Issues
Was the horn use merely an expression of intent to overtake, or did it amount to conduct that interfered with the leading driver’s attention?
Can the sequence of events — horn → sudden stop → chain collision — be legally recognized as a causal link?
How much responsibility should be assigned to a party who caused the accident without directly colliding with another vehicle?
4. Court’s Judgment and Conclusion
The horn use went beyond a simple signal and was conduct that placed psychological pressure on and distracted the leading driver.
Without the horn, the sudden stop was unlikely to have occurred, so the horn was recognized as a causal factor in triggering the chain collision.
However, the failure of the following drivers to maintain safe distances was also considered a major contributing factor.
Fault: Defendant A — 20%
Remaining fault to be apportioned among the other vehicles.
The court ordered A to pay the insurer a portion of the subrogated claim equivalent to 20% of the damages.