Signaling Back in 1913 Gustaf Dalén was interested in using radio, or as it was known at the time "sparks" as a navigational aid in fog. Early in the 1930s the development of radio technology made it possible to start using radio beacons. The signal characteristics of these beacons were far more complicated than those used previously for light and radio signals had to begin and end at specific times. . AGA’s automatic railway crossing signals which show a red light as a train approaches and green when it has passed were operated electrically and used acetylene as a source of light for many years. The first tests were carried out in Silverdal in 1918. . Railway Signals Gustaf Dalén’s flashing apparatus was suitable for providing intermittent light signals on railroads where it was used on a wide scale. The flasher could be used to give railway signals a light of a character which made it easy to distinguish from other lights. The first AGA blinking lights for railways went into operation in 1908. AGA’s signal system was complemented in the 1920s with electrical blinking lights and combinations of gas and electrical signals were also used in the 1940s. Traffic Signals The rapid growth in road traffic after the turn of the century led to an increase number of road accidents. The authorities became concerned. Using Gustaf Dalén’s flashing apparatus as a base, AGA developed economic and easily managed traffic beacons. These were in place in both the U.K. and the U.S. by 1914. In January 1925, AGA installed Sweden’s first traffic signals at the Vasagatan/Kungsgatan and Kungsgatan/Drottninggatan crossings in Stockholm. These "optical police" were the subject of lively press commentary. . In 1920 the so-called warning triangles were introduced to Sweden at the initiative of the Royal Swedish Automobile Association. In the same year AGA began experimenting with reflectors for these. This resulted in AGA’s reflector prisms which were later used in the AGA Geodimeter and in 1969 were used as laser reflectors on the moon. By 1937, 4,300 AGA traffic beacons had been set up in the U.S. The increasingly intensive city traffic required devices which could direct motorists. AGA made electrical traffic lights with signal lights in different colors which could be manually or automatically controlled.