**2. Overview of ITS applications at signalized intersections**

In this section, an overview of ITS components and applications at signalized intersections is discussed. This overview will provide the needed foundation for understanding the major components of ITS to better appreciate the cybersecurity issues discuss in a later section.

#### **2.1 Components in traffic signal systems**

The modern traffic intersection consists of various sensors, controllers, malfunction management units, and communication devices. **Figure 1** illustrates some common devices found at intersections.

Sensors employing ultrasonic, microwave, and radar technology, as well as induction loops and video cameras are all used to detect traffic conditions at intersections. The induction loop is the most popular sensor for vehicle detection. These devices are buried under the pavement and detect vehicles by measuring a change in electric current due to the metal body of a vehicle. Video cameras are also frequently used at intersections, and rely on computer vision software to detect and classify vehicles. It is worth noting that video traffic detectors are usually stationary. Additionally, cameras are installed to provide live and steerable video feed to traffic management centers. Microwave, radar, and ultrasonic sensors are less common, but can be used for special applications. Aside from detecting fine-grained vehicle presence, Bluetooth/Wi-Fi traffic detectors are sometime installed at intersections to track vehicle travel time and speed. These sensors detect and time-stamp a Bluetooth/Wi-Fi MAC address from smartphones and in-vehicle hands-free audio, then use the time-stamps of subsequent detections of that address to determine vehicle travel time across known distances between sensors.

Controllers are responsible for setting light timing patterns at intersections. Sensors are directly connected to the controller, allowing it to adaptively adjust signal timings based on traffic conditions. Traffic signal controllers can operate in several modes: 1) pre-timed, e.g., signal states change with predetermined intervals; 2) actuated, e.g., one or more directions are green, based on sensor input; 3) coordinated, e.g., controllers of nearby intersections can be interconnected to share timing information and react to sensor input. Traffic signal controllers are typically locked in a metal cabinet by the side of the traffic signal's pole.

Networking equipment for traffic signals may include both hard-wired and wireless systems. In urban areas, traffic controllers are usually hard-wired through optical or cable networks. Traffic controllers may communicate with each other and with

#### **Figure 1.**

*Main components of a traffic signal system [28].*

traffic management centers. When intersections are geographically distant, wireless systems are frequently used. According to FCC regulations, these wireless systems operate on the ISM band at 900 MHz or 5.8 GHz, or in the 4.9 GHz band allocated for public safety. Communication between sensors has traditionally been connected to the traffic controller through a direct line. If wireless sensors are used, an intersection may be equipped with access points and repeaters to process, store, and relay data. Wireless systems for traffic signal controllers and sensors usually run on proprietary protocols derived from IEEE 802.11 or IEEE 802.15 standards.

Malfunction Management Units (MMU), also known as conflict monitor units (CMU), are hardware-level fail-safe mechanisms. The MMU monitors the outputs of the controller, and if a fault is detected (e.g., green signaling in all directions, or too short of a red light duration), the MMU overrides the controller and forces it to switch the intersection to a known-safe configuration (e.g., red lights flashing for all directions). While MMU prevents displaying a potentially hazardous combination of signals, its safe configurations are pre-defined and thus suboptimal. If the MMU detects a fault state, it requires manual intervention to reset.

Traffic Control Center, also known as traffic management center (TMC) or traffic operations center, is the facility that monitor and control transportation-related information, and coordinate responses to traffic incidents. Traditional traffic control center uses closed-loop network equipment (such as video camera and vehicle counters) to monitor traffic condition and coordinate construction activity, roadway advisories, incident management etc. As traffic control centers are moving toward

*Intersection Management, Cybersecurity, and Local Government: ITS Applications, Critical… DOI: http://dx.doi.org/10.5772/intechopen.101815*

providing intermodal, interregional and interagency traffic management services, their increasing complexity leads to increases in vulnerability of cyber-attacks.

#### **2.2 Technologies for signalized intersections**

While the traffic management infrastructure was traditionally built on closed, proprietary systems, the industry is currently on a journey to switch to more connected, responsive and secured networking. Virtually all aspects of a transportation management system are susceptible to cyber threats [2]. Nevertheless, the change to a connected system must happen due to increasing traffic demands, maintenance costs, and the complexity of legacy systems. On the other hand, consumers are demanding new transportation solutions that can provide safer, more efficient, and sustainable travel options. To this end, a wide range of transportation technologies have been proposed. What follows is a brief review some of the most important general applications.

ATMS/Central System: Advanced traffic management systems (ATMS) consist of transportation management centers, field infrastructure, and mobile units communicating in real time to monitor and manage transportation systems. Real-time traffic data from cameras, speed sensors, etc. are sent into a central system where it is integrated and processed (e.g., for incident detection), and may result in actions taken at traffic infrastructures (e.g., change of signal timing, roadside messages). ATMS are the commend centers for reducing congestion, enhancing safety, and providing faster emergency response times. The main functions of an ATMS are: signal performance measurement, system assessment (collecting data), strategy determination, strategy execution, and strategy evaluation.

Dynamic Message Signs: Dynamic Message Signs, also known as Variable Message Signs, are the large, electronic signs which overhang or appear along roadways. The signs are typically used to display information about traffic conditions, travel times, construction, and road incidents.

Adaptive and Coordinated Signal Control: Adaptive signal control refers to technologies that capture current traffic demand data using sensors such as induction loops, and adjust traffic signal timing to optimize traffic flow accordingly. Coordinated traffic signal systems attempt to further improve efficiency by creating a green wave along multiple intersections (e.g., a long string of green lights) (e.g., progression) for drivers. The objective of adaptive and coordinated signal control is to provide effective signal timing settings within a range of operating conditions. It works by collecting current demand information from sensors (e.g., advance detection), evaluating performance using system specific algorithms at a central controller, and then implementing modifications based on the outcome of that evaluation via a communication network.

Transit Signal Priority and Emergency Vehicle Priority: Transit signal priority (TSP) is a set of operational improvements that modifies signal timing to favor transit vehicles (e.g., busses). TSP reduces dwell time for transit vehicles by holding green lights longer or shortening red lights. TSP systems require four components: a detection system aboard the transit vehicle; a priority request generator which can be aboard the vehicle or at a centralized management location; a strategy for prioritizing requests; and an overall TSP management system. Emergency Vehicle Priority (EVP, also known as signal preemption) is a similar application designed for special events such as a responding fire engine or police car. EVP and TSP applications can be built on a similar infrastructure, with the major difference being that signal preemption interrupts the normal signal operation rather than adjusting current signal timing.

Eco-Signal: The basic premise of the Eco-Signal concept is that if a driver has accurate information about the upcoming signal status, the vehicle speed can be adjusted accordingly to avoid stops and vehicle operation associated with increased fuel consumption (e.g., hard acceleration maneuvers). Eco-Signal application requires Signal Phase & Timing (SPaT) information from traffic controllers, which is a standard function of connected vehicle-ready traffic controllers (SAE J2735 standards). Several companies are working on commercializing such applications. They solicit traffic signal timing information from local agencies and offer a share of their revenue.

V2V/V2I Communication: V2V and V2I communication are the enabling technologies of Intelligent Transportation Systems. Vehicle to vehicle (V2V) communication is the ability to wirelessly exchange information such as speed and position between vehicles. This allows vehicles to broadcast and receive directional messages creating a net of "awareness" of other vehicles in proximity. Vehicle to infrastructure (V2I) communication is the ability to wirelessly exchange information with a structure such as a traffic signal. This can be used to gather information on traffic and road conditions. There are two mainstream technologies used in V2V/V2I communication: 1) cellular networks, such as 5G and 4G LTE, and 2) Dedicated Short Range Communication (DSRC). Cellular networks relies on cellular infrastructure along the road, while DSRC only connects vehicles in their vicinities and works in an ad-hoc manner.

Bluetooth/Wi-Fi Traffic Probe: As mentioned in Section 2.1, a basic Wi-Fi/Bluetooth sensor system for traffic monitoring consists of a Wi-Fi/Bluetooth probe device that scans for other Wi-Fi/Bluetooth-enabled devices in its radio proximity (usually within 90 feet), and then stores the data for future analysis and use. These applications may include measurements of traffic presence, density, and flow, as well as longitudinal and comparative traffic analysis.

Third Party Traffic Data: The rise of smartphone and in-vehicle apps allow largescale vehicle probe data to be collected in real-time. Third party traffic data collected by companies such as Waze and INRIX can be used to improve traffic management.

Public agencies traditionally use third party data in an aggregated fashion such as origin-destination analysis, operation monitoring, and performance measurement. In recent years, there is a growing interest to integrate third party traffic information into Advanced Traffic Management Systems (ATMS) for real-time signal timing adjustments.
