Topic summary
side mirror
Extracted from the Wikipedia article Side-view mirror.
Optional side mirror
Through the 1940s, most roads had just two lanes, one in each direction. Drivers usually had to be aware only of traffic ahead of and directly behind them. Due to this, early cars had just a single rear-view mirror mounted on the top of the windshield or on top of the dashboard. When side mirrors were introduced to help drivers see overtaking vehicles, most cars had only the driver-side mirror as standard equipment. A passenger-side mirror was optional on most cars through the 1970s. Today all 3 mirrors are standard on almost all passenger vehicles.