This question is way too basic and can be answered with a single link:
In 1912, New York, London and Paris traffic counts all showed more cars than horses for the first time.
— Raymond A. Mohl: "The Making of Urban America", p124, Rowman & Littlefield, 1997.
For personal traffic transport it was even:
The turning point in the change from horse ...
For central Europe, between 1925-1930 may be considered realistic.
For France possibly sooner due to a higher motorized density between 1920 and 1930.
The transition was uneven due to certain conditions
commercial was faster than private motorised vehicles
but the private use was probably a much smaller percentage than commercial, so in a city a ...