Japan joined the Convention on Road Traffic in 1967 in which vehicles of all member nations were driven on the left hand side of the road.
Railroads were being laid one after another since the laying of the railroad between Shimbashi and Shinagawa in 1872 and when comprised of two tracks, they were already being driven on the left side following the British system. Even cars were driven on the left side of the street. Vehicles drive on the right in the U.S. and there are many Americans who are thrown into confusion when they come to Japan, but there are many countries where vehicles are driven on the left side of the street.
The present traffic rule in Japan of assigning people to the right and cars to the left was enacted on May 20, 1949. The “people to the right” rule was designated because vehicular traffic ran on the left side of the street and it was assumed that walking when facing traffic would minimize the danger of accidents occurring. However, human beings seem to have an inclination to walk on the left side.
However, the reason may simply be that there are more right–handed people than left–handed people not only in Japan but throughout the word. Walking on the left side leaves the dominant hand free with ample room to move freely.