Methodology for Ensuring the Required Level of Traffic Safety at Single-Level Regulated Roads Intersections

. A functional flowchart is presented for the results of the investigations aimed at development of the methodology for automated control systems (ACS) which could evaluate and maintain the required traffic safety (TrS). The flowchart can be used in traffic management schemes (TMS) at regulated (signal-controlled) road intersections (RRI) with various methods of traffic light control in the options with traditional control methods I (phase by phase control) or II (control according to separate directions of traffic) and a new method of combined control of traffic III (various combinations of traditional methods I and II in one cycle of traffic light control). The control methods in ACS at RRI are changed according to the intensity threshold of left-turning and right-turning traffic streams to ensure the traffic safety (TrS) during these maneuvers.


Introduction
represents the variability in statistics of the lethal cases occurred in road accidents (RA) during the latest 29 years in the territory of the Russian Federation (RF) after its targeted-oriented processing in absolute and relative units.
According to the road traffic accidents statistics out of the total number of road traffic accidents in the RF -173,700 people in the year of 2016 alone 20,308 people were killed and 221,140 people were wounded. Every year more than 8,000 pedestrians are killed and more than 55,000 wounded in road accidents in the RF.

Theory
Social and economic losses from deaths in road traffic accidents in the Russian Federation can be calculated with the use of the recommended evaluation methods according to Table  1 -evaluation and calculation of norms for social-economic losses in road accidents [1]. The developed European countries have decreased the social risk to be killed in road traffic accidents by tens of times, up to 3 -5 persons per 100 thousand of people, and today Russia faces the problem that each per cent in the reduction of road accidents will take more and more effort [2]. That is why the authorities at all levels should employ the scientifically feasible methods to discover the reasons of the high number of casualties in road traffic accidents at any point in the complex "driver-vehicle-road-environment" (DVRE), as guidelines to significantly decrease the lethality rates. The results and conclusions obtained from the research work conducted by the order of Saint-Petersburg administration can prove these facts [7]. This research has discovered that the lethality is above 20% in the currently functioning regulated road intersections (RRI) alone. These results are scientifically substantiated during the development of a low-cost methodology to ensure traffic safety at regulated road intersections of road networks in metropolitan cities [8], as presented in Figure 2 -by a functional flowchart of the results of the investigation. The methodology is a totality of the developed methods that are functionally related to the common cause to significantly decrease lethality in road traffic accidents with the widely used automated traffic control systems (ACS) at RRI (block 1 highlighted by a dashed line in Figure 2) due to the use of innovative solutions in traffic management schemes (TMS) with conflicting events (CE). For such TMS with CE we have developed the control methods for conflicting load ratios with new methods of the diagnostic (RPl) and updated (RPlmax) evaluation of traffic safety (TrS) within the framework of the developed conceptual system (block 2) for the level of requirements for the traffic safety (LRTrS) in accordance with the intervals of traffic safety presented in Table 2 [11] and with consideration of the classification [9]   The investigations of ACS with conflict situations in TMS with CE at RRI were conducted both by the traditional control methods (I) -with phase by phase control, and (II) -with control according to separate directions of traffic [4,5,6,13], and along the new method of combined traffic control (III) [10]. The method III can combine the traditional methods I and II in one cycle of the traffic light control in ACS at RRI to provide the limits for the level of requirements for traffic safety and the required traffic capacity. At the same time, the method III ensures the automated minimizing of the number of conflict situations [1,12,14,15] (points of conflict), as allowed by the Traffic Regulations of the RF for maneuvering in the vehicles and pedestrians streams (VPS) at RRI.

Conclusions according to the results of the investigation
In order to detect the reasons for road traffic accidents at single-level regulated and nonregulated road intersections (RRI and NRRI) within the scope of road networks of any city, town or township both in the RF and abroad a scientifically substantiated method can be used for low-cost diagnostic audit (when the traffic intensity VPS is not required -only the types and quantities by the types of points of conflict at TMS with CE are required) of LRTrS [2] (RPlmax). The audit can be called the inventorying of traffic safety along the set norms (e.g., as shown in Table 2) with the corresponding records of the results level required by the customer for traffic safety out of the set range: IncrLRTrS, IntermLRTrS or AccLRTrS.
If an inacceptable level of requirements for traffic safety is detected during the diagnostic works for a single-level RRI or NRRI, the modernization is immediately ordered for the road section related to traffic accidents. During the modernization, an updated calculation shall also be conducted for the ensured level of TrS (RPl) [2].
The recommended period for repeated inventorying for LRTrS at RRI and NRRI is 3-5 years.