"According to a 2022 study from the Environmental Protection Agency, the average weight of a car is 4,094 pounds."[1]

Going from 1 person of 200lb to 4 people totaling 800lb (in a 4,000lb car) increases the damage by less than an additional car (4,800 / 4,200) ^ 4 = 1.71

[1]: https://finance.yahoo.com/news/average-car-weight-140033718....