However, there are still many problems with the use of these devices. Regulations adapting their application were only introduced in 2017. Their application took place on many continents, but in Poland, they were used was ahead of legislative changes ( Figure 1). At the turn of the first and second decades of the 21st century, devices indicating how long a given signal would be displayed, called Signal Countdown Timers (SCT), began to be used. ![]() There are fewer articles regarding traffic signals compared to other elements of traffic infrastructure, e.g., roadways, junctions, and interchanges. Research conducted in Poland has investigated issues of road lighting, in particular pedestrian crossings, adaptation of road infrastructure to the needs of autonomous vehicles, road interchanges, safety at pedestrian crossings and country highways. Issues related to road safety at intersections are a current problem. Only a short period, lasting for one or a maximum of a few seconds during the amber, and red with the amber, signals notify drivers about the signal to be displayed next. The rules set out in the above-mentioned international regulations indicate that drivers are not informed in advance about the signal change. Drivers are obliged by the law to follow the indications of the traffic light. Similar provisions were agreed in the Convention on road signs and signals established at Vienna on 8 November 1968, and allowed the use of directional signals. The convention allowed two-color signaling (red and green) and specified the meaning of individual signals. The signals used on roads were defined in international agreements such as the Geneva Convention on Road Traffic, signed on 19 September 1949. In the first years of their operation, traffic light solutions were very different but, fortunately, they were unified. ![]() A third color, amber, was introduced in 1920 in Detroit, which improved traffic safety. The colors red and green were used for the first time as signals in 1917 in San Francisco. Signaling displayed the words “STOP” and “MOVE”. The very first, based solely on light signals, was used in 1914 in Cleveland. Electric traffic lights started to be used in the second decade of the 20th century. The first traffic light was installed in 1868 at a road junction in London. Conclusions can address various stakeholders, including drivers, road authorities, and traffic engineers. The article concludes that SCTs do not always fulfill their role in improving road safety and control efficiency. A literature review also indicated that the use of SCT causes a reduction of start-up time (positive impact) and increases vehicle speed (negative impact). ![]() On the other hand, the number of entries during the amber signal with SCTs is lower. It was observed that SCTs increase the number of red-light violations and during the red-amber signal. The research shows different influences of signal countdown timers at various intersections. Problems related to signal countdown timers working during traffic light failure are described. Additionally, a fuel consumption analysis and a case study of a road crash in Szczecin (Poland) are presented. Headways, incidences of vehicles passing through after the end of the green signal, and red-light violations were examined. ![]() The initial and final period of the green signal for vehicles was analyzed. The research involved measurements carried out at three intersections in Płock (Poland). During a literature review, more than 18 aspects of device use were recognized. The impact of these devices on road safety and the effectiveness of traffic lights is presented. These devices are used in many countries around the world. This article describes the safety and effectiveness issues related to signal countdown timers (SCT).
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