Date of Award


Degree Name

Doctor of Philosophy


Civil and Construction Engineering

First Advisor

Dr. Valerian Kwigizile

Second Advisor

Dr. Jun-Seok Oh

Third Advisor

Dr. Zachary D Asher


Connected and Automated Vehicles. Highway Traffic Streams, Roadway Capacity


Autonomous vehicles have recently gained the attention of researchers due to their expected potential benefits on highway traffic streams, such as improving roadway capacity, among others. It is imperative to investigate how these expected benefits can be leveraged in the transportation sector. Understanding the safety and operational benefits helps the concerned transportation agencies and other key stakeholders to make necessary infrastructural and policy adjustments to accommodate such future traffic operation changes. The main goal of this dissertation is to study the impact of connected and automated vehicles on freeway capacity. The simulated environment was created to emulate autonomous vehicle behaviors, connectivity between vehicles, and various scenarios that answer research questions to achieve the research goal.

The first case study uses simulated traffic flows at different percentages of human-driven heavy vehicles (HDHVs) and automated passenger cars (APCs) to investigate the impacts of both HDHVs and APCs on freeway capacity. In addition, the future applicability of the current design guidelines presented in the Highway Capacity Manual (HCM) is investigated. This case study provides information on how passenger car automation affects freeway capacity. Also, a modified formula is proposed in place of the current HCM formula for determining vehicle adjustment factors due to HDHVs and APCs in the traffic stream capacity. Also, a modified formula is proposed in place of the current HCM formula for determining vehicle adjustment factors due to HDHVs and APCs in the traffic stream.

Another case study investigates the impact of connected and automated heavy vehicles (CAHV) on freeway basic section capacity. Various simulations were conducted considering the percent of human-driven heavy vehicles (HDHV) in the mix, platoon size, and percent of CAHV on HDHV and lane restriction. The simulation results provide insights into how these factors impact the freeway's capacity. In particular, freeway capacity significantly increased with CAHV and lane restriction scenarios. The increase in capacity was apparent at a higher percentage of trucks in the traffic mix. Regarding CAHV platoon size, the capacity does not appear to significantly change with platoon size for a given percent of trucks in the traffic mix.

Furthermore, a system-wide case study is conducted in Michigan, covering all the interstates. The model developed using simulated results is used to assess how the introduction of CAHVs alters the current capacity and their respective level of services without incurring any infrastructural changes. The observed positive benefits at the system-wide level are discussed, and recommendations are provided to transportation agencies.

Lastly, the study investigates how the adoption of connectivity and automation in the vehicle industry will strengthen transportation equity, especially for people with disabilities and non-motorized user groups. The survey on non-users was used to identify factors associated with differences in the perception of the feasibility of the autonomous shuttles for solving the first and last-mile travel. The results provide insight to transportation planners on the possibilities of solving the first and last mile problem among people with disabilities. At the same time, they provide information about the concerns of the non-motorized users should the technology be adopted and operated on the same infrastructure as those used by the non-motorized users.

Access Setting

Dissertation-Open Access