# The State-of-the-Art of Coordinated Ramp Control with Mixed Traffic Conditions

## TL;DR

This paper reviews recent advances in coordinated ramp control strategies that integrate both human-driven vehicles and connected automated vehicles, addressing the challenges of mixed traffic conditions for improved traffic management.

## Contribution

It proposes an innovative system architecture and reviews key components for system-wide ramp control in mixed traffic environments, filling a research gap.

## Key findings

- Extensive literature on traffic state estimation and ramp metering in mixed traffic.
- Identification of key components for coordinated ramp control systems.
- Highlighting the potential of CAVs to improve traffic flow and safety in mixed conditions.

## Abstract

Ramp metering, a traditional traffic control strategy for conventional vehicles, has been widely deployed around the world since the 1960s. On the other hand, the last decade has witnessed significant advances in connected and automated vehicle (CAV) technology and its great potential for improving safety, mobility and environmental sustainability. Therefore, a large amount of research has been conducted on cooperative ramp merging for CAVs only. However, it is expected that the phase of mixed traffic, namely the coexistence of both human-driven vehicles and CAVs, would last for a long time. Since there is little research on the system-wide ramp control with mixed traffic conditions, the paper aims to close this gap by proposing an innovative system architecture and reviewing the state-of-the-art studies on the key components of the proposed system. These components include traffic state estimation, ramp metering, driving behavior modeling, and coordination of CAVs. All reviewed literature plot an extensive landscape for the proposed system-wide coordinated ramp control with mixed traffic conditions.