I cannot answer John Burnell’s questinns directly, but my copy of the 1913 Michelin Guide to the British Isles (published about March/April 1913) gives some interesting information on the rule of the road in Europe at that time as follows:
There was a theory a few years ago that accident rates were lower in countries with a left hand rule of the road. This promoted Dr. Mackay of Birmingham University to find out how the World is divided on this. He found in the late 1970’s, that the World, with the exception of China, was almost exactly divided equally on a population basis. China remained an exception for some time as the Embassy in London did not know on which side of the road vehicles drove in China and had to refer the question to Peking. It eventually turned out that the Chinese drive on the right.
A final (useless?) piece of information is the effect of the rule of the road on the weather! An American researcher in the 1970’s (I forget who and when and I have lost my copy of the report) proposed the theory that passing lines of the traffic generate circulating air currents that add to the natural air circulation generated by the rotation of the earth. This natural air circulation is caused by the same effect that gives a predominant left or right hand circulation to water going down a plug-hole, depending on which hemisphere of the earth you are in. He correlated the increase in cyclones in North America this century with the increase in motor traffic and concluded that the “correct” rule of the road was left hand in the Northern Hemisphere and right hand in the Southern.
Whilst these modern theories were not available to the French government in 1912, the situation as set out above which prevailed then makes a proposal for the French to change their rule of the road less implausible than it would seem today.
Bromley. Kent P. E. WATERS