Charles Adler, Jr. (June 20, 1899 – October 23, 1980) was an American inventor. An engineer, he invented a number of safety signals, some of which are still in common usage.  Charles Adler, Jr. was a lifelong resident of Baltimore, Maryland. At age 14, he formally started his career as an inventor when he received a patent on an electric automotive brake. After high school, he attended Johns Hopkins University and during World War I served briefly in the US Army. In 1919 Adler became associated with the Maryland and Pennsylvania Railroad (better known as the “Ma and Pa”) and developed a series of safety and signaling devices.

On February 22, 1928 Adler installed a device he had invented to control automotive traffic at the intersection of Falls Road and Belvedere Avenue (now Northern Parkway) in Baltimore. It was the first modern traffic light.  On February 4, 1929 Adler installed a pedestrian push button at the intersection of Charles Street and Cold Spring Lane in Baltimore. It was the first pedestrian-actuated signal.  In 1937 Adler changed railroads and became a consultant to the Baltimore and Ohio Railroad. He had his office and laboratory at the north end of one of the B&O’s stations, Mount Royal Station, where he continued to invent safety and signal devices for pedestrians, automobiles, trains and airplanes.  Charles Adler, Jr. was granted over 60 U.S. patents for devices in general use today. He was also a licensed pilot and donated ten aircraft device patents to the U.S. Government. One of these was his patent for an “External lighting system for airplanes” – the familiar flashing lights on planes.