and Baltimore County, Maryland. The double-red ball aspect is used in Saskatchewan and Alberta, Canada, to indicate a protected-prohibited left turn signal. A sign with the universal no left turn symbol and a depiction of the double red light is mounted near the signal to indicate that no left turns are permitted on a double-red light. Intersections with this configuration are quite common in Saskatoon, Calgary, and Edmonton. According to Transportation Alberta, there is no legal significance to a double red light. In some cities in Mexico, the double red light is treated as a standard red signal, with the double light's purpose being to increase the signal's visibility as well as providing a redundant light in case one of failure of one of them. Clock-type These so-called "Heuer-Ampeln", developed by the German Heuer-Hammer company were used in the Netherlands, Austria (Vienna) and Germany from the 1930s until the 1960s, with the last of them being replaced with the by then common known traffic lights in 1972. Bar signals In Tianjin, One system is where there is a horizontal bar in a specific colour, with the colour changing and the bar shrinking. The shrinking bar indicates the time remaining in that colour. The colour itself is either red (stop), yellow or green (go). A blinking green one-third-full bar means "reduce speed now", and a blinking yellow full-bar indicates "proceed with caution". When lights of this system turn from green to red, the diminishing green bar will flash once two-thirds (note: not the full bar) of the green bar is "eaten up", with the remaining third intact. A full, uninterrupted yellow bar will appear for a few seconds before, after a short blink, lights turn red. Immediately after the full red bar appears, a tiny (almost unnoticeable) split/division appears to signify the bit that will not be "eaten up". This corresponds to the usual position of a red light (leftmost, or rightmost if at the other end of the road and at the other side of the pavement; or the upper third). When two-thirds of the red bit is "eaten up", the red light extinguishes, only to be replaced nearly immediately with a full chunk of green (again with the minute division). The process then repeats itself. Multi-colour aspects Another system, which is also common in the other cities in China, is where there is a set of three lights as