BACKGROUND

Advances in the automobile industry, along with the introduction of automated and electric vehicles, have changed vehicle dynamics when navigating curves, particularly in superelevation transitions and fully superelevated sections. Side friction factors based on older vehicle models may no longer align with modern vehicles, vehicle dynamics technologies such as electronic stability control, tire technologies, and pavement surface courses.

Given the advancements in the vehicle fleet, alternative design models should be evaluated for their ability to account for factors such as grade and acceleration/deceleration. Research is needed to update superelevation design criteria based on the impact of these advancements to ensure that horizontal curve designs meet or exceed the safety and performance standards required by modern vehicles and roads.

OBJECTIVE

The objective of this research is to develop performance-based superelevation design criteria. The criteria shall be based on the interaction between vehicles and horizontal curves, performance measures related to safety and user comfort, and acceptable design and construction tolerances.

Accomplishment of the project objective will require at least the following tasks.

TASKS

Task 1. Conduct a literature review of research on factors affecting superelevation design criteria including but not limited to:

• tire-pavement friction based on current tire technology and common pavement surface courses in wet/dry and varying temperature conditions;
• vehicle fleet composition (e.g., size, weight, center of gravity);
• vehicle dynamics technologies (e.g., electronic stability control, suspension, other vehicle performance/safety innovations);
• vehicle operation (traditional human-driven vehicles, driving automation systems, and mixed-fleet operations);
• performance measures related to safety and user comfort;
• design and construction tolerances (e.g., determining the appropriate interval for superelevation design); and
• alternative design models for superelevation design beyond the point-mass model.

The review shall include published domestic and international research, databases, and past surveys and outreach to public and private organizations to secure access to relevant unpublished documents and resources.

Task 2. Evaluate the current and ongoing research and identify components requiring additional study to accomplish the project objective.

Task 3. Based on the needs identified in Tasks 1 and 2, propose the research plan to be executed in Phases II and III to achieve the research objective. At a minimum, the research plan shall include a framework for:

• establishment of the appropriate spectrum of design vehicles;
• engagement with the Society of Automative Engineers On-Road Automated Driving Committee, the Infrastructure Needs task force, original equipment manufacturer vehicle providers, and similar stakeholders to understand the characteristics of the vehicles and their technologies;
• evaluation of the superelevation design models (e.g., point-mass model, multibody simulation model, vehicle dynamic model) considering factors such as grade and acceleration/deceleration;
• updating the design criteria (e.g., side friction factor [f], superelevation rate [e], distribution of e and f, superelevation transitions, design speed, curve radius, the minimum radius for the normal crown and the maximum superelevation, the minimum length to maintain the superelevated curve, vertical parabolic adjustment at superelevation transition points);
• data analysis, field studies, and experimental investigation to support updating the superelevation design criteria based on performance measures related to safety, user comfort, and acceptable design and construction tolerances; and
• development of draft language for the proposed updates to superelevation design criteria for consideration by the American Association of State Highway and Transportation Officials (AASHTO) for incorporation into a future update of the AASHTO Green Book’s chapter on Elements of Design (herein called the AASHTO Deliverable).

Task 4. Prepare Interim Report No.1 that documents the work performed in Tasks 1 through 3 and provides an updated work plan for the remainder of the research. The updated plan must describe the process and rationale for the work proposed for Phases II and III. 

PHASE II – Execution

Task 5. Execute the work plan based on the approved Interim Report No.1.

Task 6. Prepare and submit a preliminary draft of the AASHTO Deliverable based on the results of this work.

Task 7. Prepare Interim Report No. 2 that documents Tasks 5 and 6 and provides an updated work plan for the remainder of the research. The updated plan must describe the process and rationale for the work proposed for Phase III.

PHASE III – Final Deliverables

Task 8. Revise the draft AASHTO Deliverable based on approved Interim Report No. 2 for the NCHRP panel’s review.

Task 9. Present the research findings to appropriate AASHTO technical committees to collect comments for potential revisions to the AASHTO Deliverable. Update the AASHTO Deliverable considering comments.

Task 10. Prepare a stand-alone technical memorandum titled “Implementation of Research Findings and Products”.

Task 11. Prepare presentation materials, in PowerPoint or other formats, for webinars.

Task 12. Submit the final deliverables, including (1) a final report that documents the entire research effort, (2) the AASHTO Deliverable, (3) the Implementation of Research Findings and Products technical memorandum, and (4) the presentation materials.

STATUS: Proposals have been received in response to the RFP. The project panel will meet to select a contractor to perform the work.