# Connected Vehicles: Technology Review, State of the Art, Challenges and Opportunities
## 1 Introduction  
According to the World Health Organization (WHO), annual traffic accidents account for 1.3 million, and it is considered the first cause of death among young people aged 5-29 years old [1]. According to WHO statistics, every 24 s, a fatal accident occurs. Even with the presence of many preventive safety measures such as airbags, antilock brakes, and other built-in technologies that can help many people involved in accidents to survive, the number of traffic accidents continues to rise. The impact of traffic accidents is not only restricted to increasing the number of road fatalities and injuries but is considered a prime factor in holding back economic growth. The economic losses and monetary burden associated with traffic accidents have an adverse and significant impact on society. As these substantial economic losses arise from the cost of health services provided for injured people or productivity losses due to death or disability [2]. For instance, in the U.S., an annual estimation of USD 1 trillion accounts for an economic toll with a breakdown of an actual cost of USD 27 billion and USD 577 billion associated with productivity loss and a decrease in the life standards of injured, disabled, or killed people and their families [3]. Consequently, innovative and industrial automotive networking solutions have emergedout of necessity to address many safety and non-safety issues. These solutions included the introduction of connectivity into vehicles named connected vehicles (CVs), which, as a result, has been reshaping the transportation industry. These intelligent vehicles exchange traffic data among each other and with their surroundings to provide a better vehicle awareness and hence reduce road fatalities and traffic jams and provide a safe and convenient driving experience [4]. Generally speaking, CVs create new data-rich environments that enable many applications and services to make our roads safer, less congested, and more eco-friendly, while making our rides more enjoyable and productive. These applications include, but are not limited to, connected in-vehicle infotainment (IVI) systems, real-time navigation and routing, traffic information, safety warnings, accident avoidance, advanced driver-assistance systems (ADAS), automated driving systems (ADS), remote diagnostics, prognostics, repair or teleoperation in case of mal-functioning ADS, data monetization, and fleet management. With the introduction of CVs to the automotive market, the aforementioned benefits and others are leveraged. Additionally, the wide deployment of sensor technologies within modern vehicles that aid in the design and development of various applications for traffic management, safety, and non-safety such as infotainment applications have greatly enhanced the driving experience. Even with the huge advancements in sensor technologies on transportation systems, there are still significant challenges. For instance, smart parking and reverse warning applications suffer from limitations in the fields of view beside sensor accuracy and robustness issues, since these applications depend on proximity and ultrasonic and electromagnetic sensors that are greatly affected by temperature and humidity conditions. Additionally, a lack of common recognized standards between various brands when integrating sensors with other components is another challenge that needs to be considered [5]. Therefore, the need to have advanced and efficient sensing and networking capabilities will help CVs reach their optimum potential, as gathering and collecting accurate data about their surrounding environment is a significant aspect in the connected vehicle technologies [6]. The CV global market dominance can be classified regionally. Geographically speaking, the largest share of the global CV market is currently dominated by the North American market due to their advanced and well-established networking infrastructure.