Lester Wire and James Hoge developed early electric traffic lights, but Garrett Morgan (who also invented the gas mask) patented the first three-position traffic signal in 1923. Before this, signals usually only had 'Stop' and 'Go,' which caused frequent accidents when cars from different directions met as the sign flipped. Morgan's invention added a third 'warning' position (the precursor to the yellow light), which alerted drivers that the signal was about to change. This allowed for much safer and more efficient traffic flow as cities became crowded with automobiles. Morgan eventually sold the rights to General Electric for $40,000. The traffic light is a critical invention in urban planning, ensuring safety at the millions of intersections that define modern road networks.