When did American cars get turn signals?

The formal application of turn signals in American automobiles began in 1939, when Buick first equipped its models with an electronic turn signal system controlled by relays, which indicated the turning direction by flashing the taillights. This design originated from improvements to relevant patents by General Motors engineers in 1938, with its core being the control of light flashing via a switch under the steering wheel, replacing early mechanical turn indicators (such as the 1907 mechanical hand device or 1920s arrow signs). It was not until 1940 that turn signals were extended to the headlight position and incorporated an automatic cancellation feature, gradually becoming an industry standard. This evolution demonstrates the incremental innovation of automotive safety technology-progressing from initial reliance on hand signals to mature electronic solutions, ultimately culminating in the integrated turn signal systems standard in modern vehicles.