1.2.1. Background of Regulations in Poland

The very first article related to the SCT situation in Poland was published in 2013 [14] before regulations were put in place [9]. Legally, at that time, the RSCT and GSCT were used, although their technical and functional requirements were not specified, and their use was not allowed. The article presented many legal and technical problems. It also presents issues related to road traffic engineering in designing traffic light control algorithms and signaling operation in the event of an SCT failure. Some of the problems described in this article have been resolved, while others are still relevant today.

As an extension to previous research, problems related to SCTs used in Poland have been further investigated [15]. Analyzed issues were divided into technical issues related to the assembly and supervision of signals, problems in road traffic engineering associated with the determination of displayed values and the effectiveness of traffic-actuated control, issues related to road safety, and legal issues. Although the article refers to the period in which the use of SCTs in Poland were prohibited, many problems had not been solved, nor been the subject of published research.

Due to enforcement of regulations [9], the use of SCTs in Poland was allowed from 1 July 2017, but the introduced provisions were criticized. One argument was that regulations omitted devices already installed [16]. However, it should be noted that the solutions used so far had not met safety requirements, so their locations and dimensions were not taken into account in the regulations. The limitation of SCTs to fix time control was criticized, and stricter rules on the location of these devices required.

Another literature review [17] was published after the implementation of regulations in Poland. Thirty-five bibliographic references were analyzed together with a statement of general opinion on selected factors. The methodology used for SCT research was described in another article [18]. The main goal of the research was to determine the impact of countdown timers on traffic conditions and the level of traffic safety.

### 1.2.2. Capacity Issues (Headway/Saturation Flow/Capacity/Start-Up Lost Time)

A 2005 study in Kuala Lumpur (Malaysia) [19] concerned the SCT for the green signal (GSCT). The research covered the period before and after installing the GSCT. The study indicated that the impact of installing the GSCT was small. Other research carried out in Kuala Lumpur [20] concerned the influence of SCTs on vehicle capacity at six intersections. The time intervals between vehicles moving at the start of the queue were examined (headways). Only passenger vehicles were investigated. Measurements with heavy vehicles were rejected. The study showed that saturation flow for a junction with an SCT is greater than for a junction without an SCT.

Issues related to intersection capacity were also examined in the research at intersections in Bangkok [21]. Start-up delay and headway in the initial period of the green signal (six vehicles) and the later period were examined. In the case of headway, no differences were found for the subsequent period.

Similar studies were conducted in India [22] concerning mixed traffic in conditions of queuing. Two-wheeled vehicles, rickshaws, and buses were distinguished. It was emphasized that the drivers in India showed a lack of discipline. Video recordings were analyzed with the use of Matlab. The study showed reduced time intervals at the beginning and end of the green signal using SCT.

Headway was also analyzed during start-up of a vehicle column at a junction with an RSCT [23]. The research was conducted in Guangzhou (China). The results showed a reduction in headway and increased capacity due to the use of RSCT by approx. 5% at night and approx. 10% during the day, and an even greater reduction in headway standard deviation.

Similarly, different technical solutions were explored in [24]. The comparison applies to standard traffic lights, signals with different types of light rules, and numerical SCTs. The research was conducted in Brazil. The studies showed no statistically significant effect on the headway of different types of SCT in relation to standard signaling.

Study [25] investigated the effect of RSCTs on the headway/saturation flow. The research was conducted with the SCT turned on and off for 24 h and showed that the use of the RSCT reduced start-up time by 22%. The statistically significant impact concerned only the first vehicle in the queue, regardless of the period of the day. In some cases, reduction of start-up delay was even more significant. Use of an RSCT in Bangkok reduced it by 33% [21]. Research was also carried out in New Delhi at three intersections [26] where was no influence of GSCT on saturation flow, whereas RSCT reduced start-up lost time.

Other research [12] was carried out in Kayseri (Turkey) at the approaches of two intersections where an SCT was used for the red signal (RSCT) and green signal (GSCT) at the crossroads. The study determined the start-up time distributions of the first vehicle in the queue after the green signal was displayed. A statistically significant positive effect on the start of the queue of vehicles was demonstrated but, simultaneously, an increase in the number of crossing the intersection before the green signal was noted. In study [27], the psychological aspect was not considered when analyzing drivers' behavior during vehicle start-up, pointing to the possibility of obtaining a start-up delay of 0 s, which contradicts the conclusions from [12], indicating the random nature of this phenomenon.

Study [28] also concerns starting vehicles at traffic signals. Tests were carried out in Changchun (China) at six intersections with quite long cycles (100–150 s). The research concerned an RSCT and covered the first three vehicles in the queue. In the regression models used for the analysis, nine factors related to the intersection and traffic influencing start-up delay and headway were considered and showed a reduction in both values after using the RSCT.

#### 1.2.3. Red Light Violation (RLV)

One of few studies analyzing the long-term impact of GSCT on traffic was conducted in Singapore [29]. The number of red signal violations was examined before installing the GSCT and after installation for 1.5, 3, and 7.5 months. The research was conducted at different times of the day and on different days of the week. In the first two postinstallation periods, RLVs (number of red-light violations) were lower than before the GSCT was installed. However, after 7.5 months, the number of RLVs returned to the number before the GSCT installation.

In Kuala Lumpur (Malaysia) study [19], the number of entries on the red signal was two times smaller when the GSCT was installed. However, the need for further research before using these devices was indicated. In other research conducted in Kuala Lumpur [20], the rate of RLVs was higher in the case of using an SCT.

In Bangkok, a survey was conducted with over 300 drivers constantly moving around the city [30]. An essential factor was that the cycle times used in this city were 120–240 s, twice as high as the typical values used in Poland. The research showed only a slight change in saturation flow, while the start-up lost time decreased significantly. For other vehicles, as in [25], no differences were found. The absence of SCTs increased the number of vehicles entering during the red signal. The questions in the survey related to reductions of driver frustration, turning off the engine when parked, and using the waiting time for the green signal.

A study in Chennai, India [31] examines the effects of the RSCT and GSCT across four vehicle types. An increase in red signal violations was noticed in the final period, especially among rickshaw drivers and two-track vehicle drivers. On the other hand, the number of entries at the beginning of the green signal decreased among all road users. Concerning headway, the entry time of the first vehicle was significantly reduced, and the differences were small for subsequent vehicles.

Article [32] presents research carried out at three junctions in New Delhi (India). Signal programs with cycle lengths of 165–180 s were in place at the intersections. The number of red-light violations in the final period of a red signal increased. In article [33], 44 bibliographic items regarding SCT research and other solutions influencing red signal violations are presented. Conclusions concerning the use of SCT are both positive and

negative. The main difference is in the use of GSCT and RSCT. Research carried out in New Delhi at three intersections indicated that both types of SCT (GSCT and RSCT) affected red-light violations [26].

Article [34] concerns a study carried out in Hyderabad, India, at two intersections. The research included start-up loss time and capacity. Turning off the SCT increased the number of red-light violations by about 5%. The research revealed higher speeds at intersection approaches with a working SCT.

The research in [35] was carried out following the methodology described in [18] and [36] concerning a GSCT. Crossing at the beginning of the red signal at three intersections was analyzed. A significant effect of GSCT in reducing the number of red-light violations by buses and trucks was also observed.

Research in Europe conditions is presented in article [37] including SCTs installed at two intersections in Cotonou, Greece and involved vehicle column start-up and drivers' behavior at the end of the green signal. The results showed that there were practically no early starts at intersections without an SCT. When an RSCT was used, the number increases by approx. 24%. The use of a GSCT also increased the number of vehicles stopping at the end of the green signal. At the same time, the proportion of vehicles passing on the red signal decreased, but the proportion accelerating during the amber signal increased.

A study from Ljubljana (Slovenia) [38] covered one intersection. The article presents the verification of three hypotheses concerning start-up lost time, amber violations, and red-light violations. A survey among drivers was also conducted. Concerning signal violations, a greater number of entries during the amber signal occurred with the GSCT turned off, as did red-light violations. However, with respect to violation of the red-amber signal (before the green signal), a greater number of cases occurred with the RSCT turned on. The results showed positive feedback from drivers about the SCT. However, about 30% of people indicated that SCTs can be distracting.

In Poland, the first research on driving behavior at an SCT was carried out in 2014, although SCTs were used before 2014 at intersections. Research carried out by the Municipal Roads Authority in Grudzi ˛adz [39] used a speed camera and a red-light violation camera and found that the launch of the SCT increased the number of entries on the red signal, although these offenses were registered and the drivers were punished for them. Similarly, with the inclusion of an SCT, the proportion of vehicles driving over the speed limit increased.

#### 1.2.4. Entering on Amber Signal

In a study carried out in Zabrze (Poland) it was observed that disabling the GSCT increases the number of vehicles entering the intersection during the amber signal and at the beginning of the red signal [40]. Research in [41] concerned the influence of a pedestrian SCT (PSCT) on driver's behavior. It was observed that SCTs increased the number of vehicles passing through on an amber signal and reduced the number of passages on a red signal shortly following the amber.

A study in Kayseri (Turkey) [12] observed a reduction in the number of vehicles entering during the amber signal with a working SCT, except during congestion and with significant delays at the approach. The authors concluded it was important to consider the behavior of drivers at the end of the green signal when assessing appropriate times for each signal phase. The conclusion that the RSCT did not affect traffic safety is contradictory to the findings of other authors.

A different study dealt with the termination of the green signal [42]. The research was conducted in Changsha (Hunan Province, China) at four intersections. The signaling programs had cycles of 100–128 s. Three drivers' reactions were studied: stopping before the stop line, passing through on the amber signal, and passing on the red signal. Binary logistical regression analysis was used. The study showed a greater number of vehicles passing on the amber and red signals after applying the GSCT.

The research methodology in [43] is similar to that in [42] and the same research grounds were used. Logistic regression was used to analyze the data. The probability of stopping as a function of speed and distance from the stop line was examined. The study was extended to the analysis of the method of crossing the intersection on the red signal. It was confirmed that the use of a GSCT increased the number of entries on the amber signal.

As well as GSCTs and RSCTs, there are also displays showing the duration of the amber signal. A study of these in Harbin, China, is presented in [44]. Such displays reduced the number of vehicles entering during the second, third, and fourth seconds of the amber signal. A display with the function of showing the duration of the amber signal did not change the speed of vehicles, unlike the GSCT, which caused an increase.
