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Connected Vehicle Braking Loads on Highway Bridges

Description:

Connected vehicles are expected to operate with synchronized, computer-controlled behavior. While connected vehicles offer benefits from reduced labor, improved safety, and enhanced aerodynamic efficiency, they may also impose loads on bridges that were unanticipated during design. One such consideration is that truck platoons (trains of closely spaced tractor-trailer vehicles) may brake simultaneously in response to a roadway hazard, so that a bridge is subjected to an instantaneous braking force from multiple heavy trucks in a single lane, rather than a single truck (with some nominal added factor for multiple presence) as anticipated in design. Historical braking force design assumes particular truck deceleration rates and also that the vehicle kinetic energy is entirely transferred to the bridge deck. Research is needed to validate both modern deceleration rates and the proportion of load transferred to the bridge structure. This information should then be used to aid formulation of truck platoon permitting operational guidelines to ensure commuter safety and mitigate or avoid damage to structures and reduced lifecycles.

Objective:

The research objective is to characterize braking load effects on bridges for design and rating consistent with AASHTO LRFD Bridge Design Specifications (BDS) and the Manual for Bridge Evaluation (MBE) for trucks in modern fleets operating in the freight transportation sector, and to extrapolate load effects to platoon braking scenarios.

Benefits:

The proposed research is urgently needed to provide state DOTs and FHWA an understanding of the potential impacts from connected vehicles on the nation’s existing bridge assets and identify the strengthening needs required to support connected vehicles. By understanding the impacts of connected vehicles, bridge owners can take measures to insure that connected vehicles do not unacceptably accelerate bridge deterioration, and only the most needed strengthening projects are advanced, maximizing the efficient use of limited funds. Further, this research would allow state DOT’s to incorporate design code changes as necessary into bridge replacement projects during the design phase which will minimize the financial impacts of any design code changes required to support connected vehicles. By not conducting this research, the nation’s bridge assets could deteriorate more rapidly and need repairs sooner. In addition, without this research, bridge owners may choose to unnecessarily increase their bridge strengthening(s) to over-compensate for the unknown loading impacts of connected vehicles, in order to maintain their bridges in a manner that they are confident will safely accommodate connected vehicles.

Related Research:

Connected vehicles are projected to rapidly change the multi-modal transportation operational landscape. For state Departments of Transportation, these changes will involve design load (re)calibrations, new load rating procedures, and evolving permitting and traffic safety procedures. Furthermore, technology for inter-vehicle communications is highly sophisticated including the ability to control braking of the platoon and the individual unit. Most current bridges were designed with the Standard Specifications where braking forces were significantly lower; therefore, the research must include a substantial effort focusing on the evaluation of existing bridges, including bearings and substructure elements which historically have not needed to be included in routine bridge evaluations. There is literature on braking forces and stopping distances, but little research on reliability-based assessment with sound validation.

This research will compile, analyze and build upon ongoing research such as FHWA’s recent research project entitled, Truck Platooning Impacts on Bridges: Phase I – Structural Safety, and connected vehicle research being performed at the state DOT level, such as bridge load rating analyses performed by the University of Nebraska-Lincoln for the Nebraska DOT Truck Platooning Effects on Girder Bridges and TxDOT’s Evaluate Potential Impacts, Benefits, Impediments, and Solutions of Automated Trucks and Truck Platooning on Texas Highway Infrastructure.

Tasks:

The following tasks are envisioned:

Task 1: Perform a literature search associated with braking studies and associated forces imparted to bridge elements, and gravity load effects of platoons and their operations. Survey state DOTs to identify design practices and standard details to address longitudinal bridge load effects. Identify currently proposed, and in-service if available, connected vehicles in the trucking industry. Synthesize findings and identify knowledge gaps.

Task 2: Conduct an analytical program to evaluate platoon load effects on representative bridge types, based on state survey and trucking industry results from Task 1.

Task 3: Perform field studies to experimentally validate and calibrate analytical predictions from Task 2.

Task 4: Perform reliability calibration and propose a methodology to address platoon braking scenarios in bridge design, rating, and permitting.

Task 5: Develop recommended changes to the AASTHO LRFD BDS and MBE.

Task 6: Provide Final Report.

Implementation:

The primary users of this research will be state DOT bridge owners. It is envisioned that they will utilize this information to:

  • Assess bridge strengthening needs to accommodate connected vehicles
  • Revise their state specific bridge design guidance and the AASHTO LRFD BDS
  • Update load ratings of bridges
  • Assess routing of OS/OW permits for connected vehicles

In addition, FHWA will be able to utilize this work when reporting to Congress on the condition of the nation’s bridges, and states’ resource requirements to maintain their bridge assets in a State of Good Repair to support the nation’s economic vitality.

The Implementation Plan will include but not be limited to the following:

  • Present to the AASHTO Committee on Bridges and Structures;
  • Provide a final report documenting the entire project, incorporating all other specified deliverables of the research;
  • Deliver a webinar to inform practitioners of the compilation of exceptions to the AASHTO LRFD BDS;
  • Present at TRB, International Bridge Conference, and other practitioner related meetings and conferences; and
  • Recommend priorities for additional research.
Sponsoring Committee:AKB10, Innovative Highway Structures and Appurtenances
Research Period:24 - 36 months
Research Priority:High
RNS Developer:Sam Fallaha, Florida DOT
Source Info:This RNS was developed by the TRB Innovative Highway Structures and Appurtenances Committee AKB10 and the University of Nebraska-Lincoln (Midwest Roadside Safety Facility).
Richard Dunne, P.E.Co-Chair, Innovative Highway Structures & Appurtenances AKB10)
Joshua Steelman Ph.D., P.E. University of Nebraska - Lincoln

Others Supporting the RNS:
AASHTO Committee on Bridges and Structures, Carmen Swanwick Chair
AASHTO Committee on Traffic Safety, Meg Pirkle Chair
Date Posted:06/28/2021
Date Modified:07/09/2021
Index Terms:Connected vehicles, Braking, Loads, Deceleration, Tractor trailer combinations, Traffic platooning, Highway bridges,
Cosponsoring Committees: 
Subjects    
Highways
Design
Bridges and other structures

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