As personal motor vehicles became more and more popular in the early part of the 20th century, the number of collisions between automobiles and trains increased. With increasing highway speeds and enclosed vehicles, simply putting a static warning sign at grade crossings proved to be a less-than-adequate way to warn motorists of oncoming trains. One of the technologies developed to solve this problem was the "wig-wag" signal, seen here. This type of signal used large electromagnets to swing a pendulum with a blinking red light back and forth, with a loud bell sounding simultaneously. Known as the "Magnetic Flagman", the Magnetic Signal Company of Los Angeles, California was perhaps the first to mass produce these signals, and they rapidly became popular at railroads all across the country. They were much more effective at getting motorists attention than static signs. They were used for decades, before the advent of more modern signals with crossing gates. A few examples of this type of grade crossing protection still exist in the US, even in the 21st Century.