LogFAQs > #978129288

Romans drove on the left side of the road.

https://www.history.com/news/why-do-some-countries-drive-on-the-left-side-of-the-road

The majority of people are right handed, one theory goes, so driving or riding on the left would have allowed them to wield a weapon with their dominant hand if they crossed paths with an enemy.
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In the United States, meanwhile, many researchers trace the beginning of right-hand traffic to the 18th century and the rise of freight wagons pulled by large teams of horses. Since these vehicles often didnt have a drivers seat, drivers tended to ride on the left rear horse to more easily control their animal team with their right hand. As the wagons became more popular, traffic naturally moved to the right so drivers could sit closer to the center of the road and avoid collisions with one another. Yet another major influence was carmaker Henry Ford, who mass-produced his Model T with a left-positioned steering wheel, which necessitated driving on the right side of the road.