# A Survey of Vehicular VLC Methodologies
## 3 Vehicular VLC Overview  
### General Context  
Congestion in emerging countries and worldwide has become of great importance due to the significant problems it causes, such as difficulty in transportation, high fuel prices, and environmental pollution issues. Moreover, the increase in the number of vehiclesoften causes accidents, according to [63], as human errors are responsible for about three-quarters of car accidents; therefore, if there are warning devices on the road, the probability of accidents will decrease significantly. Intelligent Transportation Systems (ITSs) have effectively helped address most of the abovementioned difficulties. The importance of high-speed wireless communication has increased, enabling development of these systems, which have many essential applications, including pre-collision warning and emergency braking, sensing or warning when changing lanes or before a collision, and alerts at road curves, in addition to assistance in turning and stopping movement and when violating a traffic signal [64]. Conversely, data can be exchanged between vehicles, including speed, location, engine status, acceleration, etc. Intelligent transportation systems (ITSs) have been the subject of intense research efforts over the past decades, as these systems will be essential parts of smart cities in the future [29; 65]. ITSs enable the process of exchanging information between infrastructure and vehicles. The main objective of ITSs is to ensure safety, reduce traffic, and reassure passengers. Additionally, major companies like Google, Tesla, and Uber have assessed fully autonomous vehicles as an essential standard for ITSs. Moreover, necessary enabling technologies have emerged that have helped create advanced transportation solutions. Among these solutions are vehicle-to-vehicle (V2V) and pedestrian-to-vehicle (P2V) communications, also called communications between vehicles and everything (V2X), and vehicle-to-infrastructure (V2I) communications [4]. The practical application of intelligent transportation systems requires flexible, highly reliable, and scalable solutions. Furthermore, due to the expansion of standardization activities and research efforts on vehicle communications to everything, with the majority of the work depending on RF technology, through which short-range communications (DSRC) have been used by commercial vehicle manufacturers [66], as well as due to cellular-V2X communications for the fifth generation (C-V2X), which is now being built [67], radio communications are now suitable for ITSs because vehicle communications to everything in the market have become shallow. However, the interference levels may become significant in the future, especially when conditions are congested. In addition to the restricted bandwidth, this causes a lot of delays and a low packet rate due to congestion, which affects communication channels. Therefore, visible light communication (VLC) technology has emerged as an alternative candidate or a complementary solution to address most of these problems [29; 68]. Additionally, there is widespread use of lights for traffic infrastructure, especially light-emitting diodes (LEDs), as well as headlights (HLs) and taillights (TLs) in vehicles; these lights have some of the features that make them an alternative solution to traditional halogen bulbs. Intelligent transmission systems make VLC a possible option. The most prominent features are brighter lighting levels and a high-rapidity switching function, which ensure longer lifetimes and minimize heat dissipation [16]. Over the last decade, research into VLC systems for indoor applications has received significant attention [12; 14]. Nevertheless, their uses in outdoor contexts, like vehicle communications, are still relatively new and require further research [15].