*1.1. Problems of Using Signal Countdown Timers*

The first traffic light was installed in 1868 at a road junction in London [1]. It was based on a gas lamp. Electric traffic lights started to be used in the second decade of the 20th century. The very first, based solely on light signals, was used in 1914 in Cleveland. Signaling displayed the words "STOP" and "MOVE". The colors red and green were used for the first time as signals in 1917 in San Francisco. A third color, amber, was introduced in 1920 in Detroit, which improved traffic safety. In the first years of their operation, traffic light solutions were very different but, fortunately, they were unified. The signals used on roads were defined in international agreements such as the Geneva Convention on Road Traffic, signed on 19 September 1949 [2]. The convention allowed two-color signaling (red and green) and specified the meaning of individual signals. Similar provisions were agreed in the Convention on road signs and signals established at Vienna on 8 November 1968 [3], and allowed the use of directional signals. Poland signed both of these conventions. Drivers are obliged by the law to follow the indications of the traffic light. The rules set out in the above-mentioned international regulations indicate that drivers are not informed in advance about the signal change. 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. Issues related to road safety at intersections are a current problem. Research conducted in Poland has investigated issues of road lighting, in particular pedestrian crossings [4], adaptation of road infrastructure to the

**Citation:** Krukowicz, T.; Firl ˛ag, K.; Suda, J.; Czerli ´nski, M. Analysis of the Impact of Countdown Signal Timers on Driving Behavior and Road Safety. *Energies* **2021**, *14*, 7081. https://doi.org/10.3390/en14217081

Academic Editor: Teresa Galvão Dias

Received: 9 October 2021 Accepted: 23 October 2021 Published: 29 October 2021

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**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

needs of autonomous vehicles [5], road interchanges [6], safety at pedestrian crossings [7] and country highways [8]. There are fewer articles regarding traffic signals compared to other elements of traffic infrastructure, e.g., roadways, junctions, and interchanges. 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. Their application took place on many continents, but in Poland, they were used was ahead of legislative changes (Figure 1). Regulations adapting their application were only introduced in 2017 [9]. However, there are still many problems with the use of these devices. In this article, the problem is reviewed from the perspective of research conducted around the world. Additional research was also carried out by the Road Traffic Control Team at the Faculty of Transport Warsaw University of Technology. Unexplored and unsolved problems require further research, which are indicated in the conclusions.

**Figure 1.** Signal Countdown Timer in Nowy S ˛acz, Poland (2016).

#### *1.2. Literature Review*

Issues related to drivers' reactions to changing signals have been the subject of many studies since the middle of the 20th century [10,11]. SCTs can be used both for the red signal (RSCT) and the green signal (GSCT) at crossroads [12]. The purpose of the SCT is to help the driver decide to stop or drive through at the amber signal and to start the vehicle column moving more efficiently at the beginning of the green signal. Research also shows that many drivers cross the traffic lights stopping line while displaying a red signal, which is called a red-light violation (RLV) [13].

The literature review was divided into main threads related to the behavior of drivers and pedestrians. Starting from the background of regulations in Poland (Section 1.2.1), the topic was investigated worldwide. Main problems related to vehicle traffic and SCT were categorized into subjects of capacity determination (Section 1.2.2), red light violation (Section 1.2.3), entering on the amber signal (Section 1.2.4), vehicle speed, braking characteristics, dilemma zone (Section 1.2.5), reaction time (Section 1.2.6), safety statistics (Section 1.2.7), GHG emissions (Section 1.2.8) and cycling (Section 1.2.9).

Some of the articles on SCT consider devices for pedestrians (in a shortcut later described as PSCT). The main problems covered by the research were pedestrians passing on the flashing green (Section 1.2.10), pedestrian red-light violations (Section 1.2.11), pedestrian speed (Section 1.2.12), and vehicle-pedestrian conflicts (Section 1.2.13).
