Wonder about the road damage aspect of this. If the relationship is a 4th power of weight, assuming a single vehicle with 2x the weight, it would need to replace 16 individual cars to break even.
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....