AASHTO STANDING COMMITTEE ON RESEARCH
AMERICAN ASSOCIATION OF STATE HIGHWAY AND TRANSPORTATION OFFICIALS
I. PROBLEM NUMBER
To be assigned by NCHRP Staff.
II. PROBLEM TITLE
Sensitivity of roadside factors related to vehicle rollover crashes
III. STATEMENT OF THE RESEARCH PROBLEM
Vehicle rollover crashes are a leading cause of fatalities in ran-off-road crashes. Out of the 32,000 total highway fatalities in the U.S. last year, about a third of those involve a ran-off-road event. Although rollovers represented only 2.6 percent of the total number of ran-off-road passenger vehicle crashes in 2012, they caused 20 percent of the fatalities. They are particularly dangerous crashes resulting in serious spinal and traumatic brain injury and indeed one of the largest contributors to spinal injuries in the US.
Vehicle rollovers are caused by various factors, and not all of them are completely known. Several crash databases collect data on crashes involving vehicle rollovers (e.g. FARS, NASS and CIREN, NCHRP PROJECT 17-22, NCHRP 17-43). However, very limited understanding can be developed about the root causes of rollovers by just using the crash data. Finite Element Method (FEM) computer simulations reconstructing the crash are a powerful tool that can be used to determine the root causes of vehicle rollovers and to develop a greater understanding of how these causation factors affect vehicle kinematics. Proper understanding of the rollover causation factors is essential in mitigating these factors and ultimately reducing the number of fatalities and injuries due to vehicle rollovers.
Several previous and ongoing studies have used multi-body vehicle dynamics codes to simulate vehicle encroachments, but due to limitations of modeling techniques, several assumptions needed to be made. Among these limitations is modeling the terrain using simple rigid surface with varying friction coefficients. Similarly, most vehicle dynamics codes do not have the ability to model vehicle tyre to terrain contact, which can be critical in some scenarios for vehicle rollovers. These studies also do not take into account rollovers that may result from initially impacting a roadside object such as a guardrail, tree, culvert, etc. In many situations, a rollover event is a combination of a series of consecutive events. For example, a vehicle may leave the roadway and start side-slipping on a soft soil of the roadside foreslope, then strike a culvert or some other object, and finally rollover. In such cases, deformation of the tires, interaction of the tires and soil, vehicle body contact with terrain or other objects, vehicle suspension and steering responses, etc. can greatly influence the outcome of an encroachment event.
Finite Element (FE) modeling and analysis have been extensively used in various studies to evaluate dynamic impact of vehicles and roadside objects. FE models developed under sponsorship of FHWA have been used in various research and design studies to simulate vehicle impacts with roadside safety hardware and other objects. Validated FE models can be greatly beneficial in evaluating the rollover causation factors in a more comprehensive manner. They allow modeling complex tire-terrain interaction when the vehicle starts furrowing in soil. Similarly, FE analysis allows for incorporating vehicle body-to-terrain contact, impact with other objects, and modeling of the vehicle as a deformable multi-part body with proper material properties. The aforementioned features usually cannot be modeled in vehicle dynamics codes and thus limit our current understating of the rollover causation factors.
Among the existing vehicle fleet, high center of gravity vehicles such as pickup trucks, are most commonly involved in rollover crashes. Thus at a minimum, this project should evaluate rollover causation factors using a pickup truck.
The currently available public domain FE vehicle models of pickup trucks require incorporating some additional features before they can be used for performing comprehensive investigation of rollover causation factors. Hence improvements should be made to the vehicle models.
IV. Research Objective
The objective of this project is to determine the sensitivity of various factors to the causation of vehicle rollover, such as encroachment angle and speed, terrain features, vehicle types, and types of roadside objects impacted. This project should enhance understanding these sensitivities of key causation factors of rollover crashes using finite element simulation analysis with properly validated vehicle models and using results from limited crash testing.
Among the existing vehicle fleet, high center of gravity vehicles such as pickup trucks are most commonly involved in rollover accidents. Thus, this project would evaluate rollover causation factors initially using a pickup truck model.
Necessary improvements to current FE models need to address:
- Development of tire and soil models that allow proper deformation and interaction of tires and the terrain in situations where the vehicle is side-slipping. In particular, the possibility to simulate tire de-beading would greatly enhance the accuracy of the model to reproduce the interactions between tire and soil as well as other roadside objects that the vehicle may impact before rolling over, e.g. curbs.
- Steering and suspension systems capable of simulating the failure of suspension parts during impacts with highway safety hardware or other objects.
For an accurate and reliable implementation of the above mentioned capabilities, a calibration and validation of the improved FE vehicle models is necessary. Static and dynamic component testing, with some limited full-scale crash testing will be required to collect the data necessary for model validation.
Time permitting other models could be considered.
V. Estimate of Project Funding and Research Period
$500,000 over three (3) years
VI. Urgency and Payoff Potential
Urgency – Rollovers are among the leading causes of fatalities and serious injuries, particularly spinal injuries, among all ran-off-road crashes. It is therefore important to develop a greater understanding of factors that cause rollovers. Current understanding of the rollover causation factors is limited. Enhancing this understanding is crucial for reducing fatalities due to vehicle rollovers.
Potential Payoff – Greater understanding of the key factors causing rollovers will allow preventing or mitigating these events. This will in turn help reduce the number of fatalities due to rollover crashes. A better understanding would help designers to make better informed roadside design decisions to minimize rollover risk should the vehicle depart the roadway. For instance, is a reduction in roadside slope more or less effective at reducing rollover risk than changing the offset of a longitudinal barrier?
VII. PROBLEM MONITOR
Rod Lacy, PE
Engineering Manager - State Road Office
Eisenhower State Office Building
700 SW Harrison Street, 13th Floor
Topeka, KS 66603
Office: 785-296-3901
Cell: 785-640-1952
Fax: 785-296-4302
email:
VIII. DATE AND SUBMITTED BY
August 16, 2013
Keith A. Cota, P.E.
Chairman, Technical Committee on Roadside Safety
New Hampshire DOT
7 Hazen Drive, PO Box 483
Concord, NH 03302-0483
Phone: 603-736-8811
Email: .
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