Why the vehicles in Britain keep to the left? According to the historical records, the Pope Boniface VIII issued an order for all the Pilgrims to keep to the left in the year of 1300 during the first Christian celebration. At that time, keeping to the left is regarded as a justified order. For one thing, most people are more reliable to their right hand. It’s convenient for them to do other things with their right hand given that vehicles are on the left and the right hand is always on the outside. For another thing, horse is the main vehicle at that time. People have to get on or off their horse from the left. With the help of the platform, people get on the horse and then whip a horse to gallop.