Road rage incidents are becoming common. When two Ford transit vans collided on the A46 Ashchurch Road in Tewkesbury, England on 22 November, the drivers argued,

before one of them grabbed the other’s throat causing him injury.

In Lapu-Lapu City, Cebu, on 16 December, a lawyer who refused to let a jeepney overtake him angered its driver, the local police said, according to SunStar.

The driver, and his son who was driving a multicab nearby, threatened to stab the lawyer. When the lawyer refused to get out of his vehicle, they hit his car to provoke him, damaging it.

Why road rage occurs, as some researchers have found, may be explained by exposure to lead from car exhaust.

The researchers from Duke University, Florida State University, and the Medical University of South Carolina looked at the lasting impact of car exhaust in the United States by analyzing childhood blood lead levels from 1940 to 2015. Their findings were published in the Journal of Child Psychology and Psychiatry on 4 December.

According to the findings, the national population experienced an estimated 151 million more mental health disorders attributable to exposure to lead from car exhaust during children’s early development, NBC News reports.

The exposure to lead made generations of Americans more depressed, anxious, inattentive or hyperactive, the study says, according to NBC News. It also lowered people’s capacity for impulse control and made them more inclined to be neurotic, the study adds.