Vehicle traffic on highway systems are typically not uniformly distributed. Research at University of California at Los Angeles (UCLA) introduces a protocol that exploits this phenomenon by considering the formations of shock waves and opportunities in adjacent lanes. DRIVE-EX (an extension of Density Redistribution through Intelligent Velocity Estimation (DRIVE)) is a connectionless protocol that broadcast messages when a vehicle slows down or the velocity falls below a threshold. Like the original DRIVE protocol, DRIVE-EX consists of three phases, the notification phase, the reception phase, and the forwarding phase. However, the notification and reception phases have been extended to process information from adjacent lanes (model assumes vehicles are equipped with optic sensors so that they can determine which lane they occupy).
The protocol utilizes vehicles’ velocities to estimate the flow and density between communicating vehicles, and recommends opportune lane changes to distribute the vehicle densities across multiple lanes when possible.
The performance of Drive-Ex was evaluated via simulation. Simulations were carried out using Vehicles in Network Simulation (VEINS), which couples a network communication simulator with a vehicle traffic simulator. DRIVE-EX was simulated at penetration rates of 10%, 40% and 100% on two highway topologies (one with an on-ramp, one with a bottleneck).
The study found that the protocol uniformly distributes vehicle densities across multiple lanes while maintaining lane fairness, and reduces the number of vehicles entering a shock wave point.
- For the highway configuration with an on-ramp. the protocol was found to increase velocity by 20 percent and decrease overall travel time by 20 percent (at 100 percent penetration)
- For the highway configuration with a bottleneck, the analysis shows similar improvements, however, the overall traffic performance was less in the case of the bottleneck due to the fact that the capacity of the highway takes a significant drop at the bottleneck position.
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