Keywords

1 Introduction

The development of technologies with the growth of roads caused the need of developing new technologies that support the traffic flow. Researchers not only focused on developing the vehicle itself but also on how to make vehicle interact with the surrounding environment by communicating with other vehicles V2V and infrastructures V2I. The concept of roadway automation started since 1939 where an exhibition called ‘Futurama’ was held to study the possibility of using communication and control techniques to make road traffic safe, efficient, and environmentally friendly [1]. Later in 1960s, an actual radio-based ‘roadway automation systems’ were developed and it was the first step to the evolution of ITS in general and specifically vehicular ad-hoc networks VANETs-based ITS [2]. In addition, one of the other technologies that were released in that early decade was the Dynamic Message Signs in 1960 (DMS) [3]. Also in 1960s, the Global Positioning Systems (GPS) was brought to life for military and intelligence purposes [4] which helped to enable geographic information systems (GIS) [5]. In the mid-1960s-Driver Aided Information and Routing System (DAIR) was introduced to send an emergency message to a service center [6]. Since that time, researches and development in various countries such as the USA, Japan, and Europe were motivated to develop new vehicle related technologies.

The goal of this paper is to present an overview of the main technologies and researches done in the last decades. The main purpose of these technologies is to increase the efficiency of traffic flow in different ways. We classified them based on the main purpose of VANET-based ITS: congestion avoidance, intersection control, accident avoidance and emergency management (Fig. 1).

Fig. 1.
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VANETs-based ITS functionalities.

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The rest of the paper is organized as follows. Section 2 provides a survey of VANETs-based congestion avoidance, followed by a description of recent work done on VANETs-based traffic intersection control in Sect. 3. VANETs-based emergency management will be identified in Sect. 4. Finally, Sect. 5 presents the various research solution proposed to implement VANETs-based accident avoidance systems and Sect. 6 concludes and presents future research directions.

2 VANETs-Based Congestion Avoidance

Due to high number of vehicles, we needed to avoid crowded roads and highways, so different techniques were emerged to the life that helped to avoid congestion.

2.1 Route Guidance System

Many systems have been proposed to guide drivers to right destinations in order to avoid the probability of congestion. From 1992 to 1993, the Travel Technology short for (TravTek) in V2I & I2V was applied in Orlando and Florida [6]. TravTek is navigation device and in-Vehicle information system that is used by traveler. This system was part of a project shared between private and public sectors such General Motors, in Florida Highway Department and others. The process of TravTek is as follow [7]:

  • General motors prepared 100 vehicles with special system including a dashboard and a sensitive touch screen. The information is collected and processed at the Orlando Traffic Management Center (TMC). The information and services are provided by TravTek Information and Services Center (TISC).

  • Each vehicle has its In-vehicle system that does two way communications: with TMC or with TISC both using a hands-free cellular phone.

  • When a vehicle receives broadcast of traffic information from one TMC I2V, it sends to another TMC V2I its travel reports that contains times and locations by using TravTek traffic links. This helps Florida Department of transportation and Orlando city that operated TMC collects traffic data easily from those equipped vehicles.

Another technology based on VANET, appeared in 2014, was done to route the vehicles. This system captures the current position, predicts the future position and comes up with the best routing for each vehicle. This system uses V2V communication. It is implemented using Dedicated Short Range Communications, sensors, Onboard Units (OBU), and RSUs [8].

Moreover in 2017, [9] proposed system that make vehicles use cameras to capture elements of the surrounding environment and tracking the neighboring vehicles to provide information. However, they noted some of the shortcoming in using cameras for tracking vehicles which is that a camera can provide the information about the vehicles only in their sight. On the other hand, V2V communication can provide more information regardless of their visibility. However wireless based methods also have some limitations as not all the vehicles are equipped with wireless communication and messages may experience interference. To overcome some of these shortcomings, they proposed a method of vehicle tracking which uses both wireless communication and camera to track the vehicles where each vehicle sends a map request via wireless to other vehicles in range and, based on their responses, it updates its own information.

2.2 Parking System

Zaho et al. noticed in [10] that about 30% of the traffic congestion is caused by vehicles cruising around their destination and looking for a place to park. They developed in 2012 an effective solution to solve this issue by providing guidance for the vehicles to be parked according to the occupancy status of each parking lot [10]. In their approach Location-aware-based intelligent parking guidance over infrastructureless VANETs (IPARK), the cluster formed by parked vehicles generates the parking lot map automatically, monitors the occupancy status of each parking space in real time, and provides assistance for vehicles searching for parking spaces.

2.3 Smart City System

In [11], Khekare et al. discussed and compared the different existing intelligent traffic systems as well as various routing protocols related to the proposed system. The idea of the proposed scheme is to build a smart city framework for VANET formed of intelligent traffic lights (ITLs) that transfer warning messages and traffic data between the vehicles V2V. The new scheme aims to reduce trip time and pollution and to improve the drivers’ quality of life by enabling the driver assistance device such as GPS take a proper trip decisions and avoid congested roads. Khekare et al. concluded that the best routing protocol to implement the new system is the Ad hoc On-Demand Distance Vector (AODV) [11].

In 2016, Khaza et al. worked with an aim of building infrastructures for the vehicles to communicate among themselves [12]. They suggested the Vehicular Cloud as part of smart city. Vehicular cloud combines information from mobile nodes and various RSUs, and store it in the cloud. The system then can work as follow. The mobile end-user device sends an inquiry to the vehicular network which reports the traffic profile to the alternate route-tree selection module. This approach is useful in emergency cases as the system will send number of possible medical centers that the patient may be taken to along with rout-tree.

3 VANETs-Based Traffic Intersection Control

The development of urban networks caused the appearance of complex intersections that needs new ways and algorithms to manage them. We will illustrate down three of main techniques in this field. These methods enhance the performance of intersections with respect of priorities and the needs of environment.

3.1 Traffic Controller

In 2010, Ghaffarian et al. developed a traffic controller instead of traffic lights to manage the intersections. Traffic controller uses simple integer linear program, as it manages the patterns of safe driving crossing the junction as well as maximizing the number of passed vehicles across the intersection. The safe driving patterns make sure of the safety of the vehicles moving and avoid accidents. It uses controller and Microprocessor Optimized Vehicle Actuation (MOVA). This research supports V2I communication [13].

3.2 Distributed Mutual Exclusion Algorithms (DMEA)

In [14], Zhang et al. developed a VANETs-based algorithm to solve problems that face controlling intersections. Firstly, they provided an algorithm that solved the mutual exclusion problem (MUTEX). MUTEX problem occurred when the controller of the intersection allows only one vehicle to cross at time for vehicles safety. Their algorithm has vehicle and controller tasks. Before vehicles cross the intersection, vehicles in each lane have to lock the vehicles on conflicting lanes based on a locking table by sending messages to controller who do the locking task V2I.

The centralized approach needs to deploy a new device (Controller) and we have different intersection shapes that make fault tolerant techniques difficult to apply. Therefore, they added a new approach for crossing intersections, and the new distributed approach is making vehicles compete in getting the privilege to pass the intersection via message exchange which is V2V communication without Controller interference. A priority is determined by arrival time so vehicles with high priority will prevent the one with lower priority to pass. Also, vehicles from concurrent lanes can cross simultaneously the intersection [14].

3.3 Adaptable in VANETs-Based Intersection Traffic Control Algorithm

In 2016, an improved centralized approach of [14] was introduced by Elhadef [15] in VANET based Intersection Traffic Control. Elhadef solved the flaws found in [14] and proposed a more adaptable approach. The locking mechanism proposed in [14] did not satisfy the safety property (Mutual Exclusion), and hence, there is possibility that two vehicles in conflicting lanes can get permission from controller to cross simultaneously. Therefore, Elhadef updated the locking scheme [15] that makes vehicles cross the intersection much safer. Moreover, the algorithm proposed by [14] had controller fairness problem as vehicles might be delayed after getting the permission to access the intersection. To solve the fairness problem, [15] added a timer in the controller task to allocate a finite time for each vehicle to cross the intersection when getting permission from the controller.

4 VANETs-Based Emergency Management

Once an accident occurs, we need some urgent systems that can handle the situation and limit the level of losses.

4.1 Safety System (SS) Using RFID

In 2009, a research about a safety system using Radio-Frequency Identification (RFID) was developed by Masud et al. [16]. RFID is used for pedestrian safety and proposed an extended infrastructure for vehicle safety communication using cooperative routing information on the sudden movement of the vehicle, as well as direction changes. The system works as follow, when an accident accrues, the involved vehicles send warning messages which will be forwarded to other vehicles V2V and RSUs V2I. The system uses RFID and GPS technologies, and the communication is mainly on Ultra High Frequency for the RFID [16].

4.2 Intelligent Transportation Systems and Cloud Computing

A research was proposed by Alazani et al. to manage disasters using cloud computing in 2011 [17]. Intelligent transportation systems and cloud computing both are used for disaster management in VANET environment. This system gathers information from different sources and locations, via vehicles messages V2I, especially the location of an incident to make effective decisions and strategies, and then transfer the information to vehicles in real time I2V. It uses Worldwide Interoperability for Microwave Access (WiMax) for cloud computing.

4.3 Context Aware (CA) System

In [18], Al-Sultan et al. developed a system to detect the abnormal behavior of the driver. Development of context aware system was based on analyzing the driver behavior in order to detect the abnormal behavior then warn the other vehicles on the road about it to avoid accidents by V2V communication. The system collects information about the driving environment to help in making decisions. The system also uses Dynamic Bayesian Networks (DBN) which is used to predict the likelihood of an accident. It uses multiple types of sensors and cameras, as well as GPS [18].

5 VANETs-Based Accident Avoidance

Different ways have been conducted that can control vehicles automatically in way that helps in avoiding accidents before they happen. Also, sometime we need something to warn the driver before he gets involved in accident, therefore various systems were proposed to handle these situations.

5.1 Warning Systems

As the number of accidents kept increasing, the needs for warning systems, that alert drivers about abnormal situations and hazards, were increasing as well. Truck rollover accidents were known as one of the most common type of accidents in the Washington DC highway and there were high rate of human and materials losses. Therefore in 1993, Truck speed advisory (TSA) systems have been developed to improve safety in highway [19]. These systems are using a radar or in-pavement detectors to detect trucks speed and warn drivers if they are driving too fast which improves trucks safety. There are two main applications of this system where: either the rate of danger is high on highway exit ramps, or where trucks possibly will accelerate to very high speeds, on steep downgrades. Virginia, Maryland, and Pennsylvania, in the USA, were chosen to install the system in their most 4 high risk sites based on their previous Trucks’ accidents history. Moreover, to decide whether speed is excessive or no, Truck speed advisory systems make use of special parameters for instance speed, deceleration, truck weight, radius of curvature, and super elevation. Then, when driver’s speed exceeds a given threshold, driver receives flashing beacons or message signs from these systems to slow down.

Another system was proposed by Aadil et al. in 2012 [20], and they targeted a normal driver. The vehicle warning system collects the information and transfers them to help in providing a safe travel for people, as well as a safe transport for 2shipping goods. It detects the sudden movement changes of vehicles, and then sends warning messages to authorities for post-accident scenarios. It uses RFIDs, GPS, and Cellular communication. The communication used in this system is V2I [20].

5.2 Highway System

In 2003, Sanghyun proposed an Automated Highway System (AHS). The aim of the system was to improve the performance of the USA transportation system by increasing the efficiency and number of vehicles per lane per hour. The system also aid in reducing and getting rid of human errors to decrease number of accidents [21].

The concept of AHS is about a new relationship between vehicles and the highway substructure and between vehicles itself. In highway, there is a set of selected lanes that is on limited access roadway where only equipped vehicles are operated under fully automatic control. Also, vehicle and highway control technologies are used to control vehicle movements (see Fig. 2). Moreover, driving tasks such as braking, steering and throttle is done automatically instead of the driver by using sensor, communication, and obstacles-detection technologies. Furthermore, AHS uses on-board vehicle intelligence with technologies that is installed on along highway and communication technologies that link vehicles to highway infrastructure. Consequently, both highway and vehicles work together to control, coordinate the vehicle movement and evade obstacles. Then, it improves safety and reduces congestion [21].

Fig. 2.
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Automated highway system.

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Figure 3 shows the first Automated Highway Demonstration that held in 1997 in San Diego, California where more than 20 full automated vehicles had participated [6]. They were functioning on I-15 Express Lane along road of 7.6 miles. The demonstration didn’t show the main features of future AHS but people got glance about AHS and the latest driving tasks technologies has been used.

Fig. 3.
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Automated Highway.

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6 Conclusion

This paper has presented majority of the technologies and research papers that introduced VANET-based Intelligent Transportation Systems from 1990 until 2017. We demonstrated the main contribution in congestion avoidance such as route guidance system, parking system and smart cities. We also clarified some of the most important contributions in traffic intersection management; traffic controller and algorithms such as the distributed mutual exclusion algorithm and the adaptable in VANET-based intersection traffic control. After that we illustrated 3 systems that were meant to improve emergency management. One of the systems relied on RFID communications, another one focused on intelligent transportation and cloud computing the third system focused on context awareness. Lastly, we mentioned the warning system and highway system which both contributed in avoiding accidents.

In this survey we aimed to raise the awareness of the development of VANET-based Intelligent Transportation Systems. We highlighted the foremost achievements related to the ability to avoid congestion, control the intersection, accident avoidance and emergency control and management.