Date of Award

August 2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil Engineering

Committee Member

Mashrur Chowdhury

Committee Member

Patrick Gerard

Committee Member

Wayne Sarasua

Committee Member

Yunyi Jia

Abstract

The safe freeway merging and lane-changing operation for fully Autonomous Vehicles (AVs) in mixed traffic (i.e., the presence of AVs and non-AVs in the traffic stream) is a challenging task. The AV merging and lane-changing operation could increase crash risks and reduce operational efficiency significantly in mixed traffic.

This dissertation quantifies the freeway merging crash risk and develops a freeway merging decision strategy based on crash risk assessment for an AV attempting to merge in the target lane with non-AVs. The performance of the risk-based merging decision strategy is evaluated in uncongested, near-congested, and congested traffic conditions. The analyses show that compared to the base scenarios, the risk-based merging strategy causes less abrupt acceleration/deceleration of an AV’s immediate upstream vehicle in the target lane on the freeway. The risk-based merging strategy meets the requirement for the minimum safe gap between an AV intending to merge and the immediate downstream vehicle in the target lane during the merging process. The risk-based merging strategy also produces lower crash risk in terms of Time Exposed Time-to-Collision (TET) and Time Integrated Time-to-Collision (TIT) compared to the base scenarios. Moreover, the risk-based merging strategy has a shorter merging duration and a lower impact on the average speed of traffic in the target lane compared to the base scenarios.

This dissertation also quantifies the freeway lane-changing crash risk, establishes risk models that help evaluate the lane-changing crash risk for an AV, and develops a lane-changing decision strategy based on a two-stage crash-risk minimization process for an AV intending to change a lane. The lane-changing crash-risk minimization is generated in the following two stages: (i) gap selection and (ii) lane-changing maneuvering from the current lane to the target lane. The performance of the risk-based lane-changing decision strategy is evaluated in a near-congested traffic condition. The analyses show that compared to the base scenario, the risk-based lane-changing strategy causes less abrupt acceleration/deceleration of an AV’s immediate upstream vehicle in the target lane on the freeway. The risk-based lane-changing strategy outperforms the base scenario in maintaining the minimum safe gap between an AV and its immediate downstream vehicle in the target lane. The risk-based lane-changing strategy also produces lower crash risk in terms of TET and TIT compared to the base scenario. Moreover, the risk-based lane-changing strategy has a lower impact on the average speed of traffic in the target lane compared to the base scenario.

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