CHAPTER 1

Introduction

The number of vulnerable road users continues to grow within the United States, as do crashes between motorists and vulnerable users. A large percentage of the nation’s roadways have limited space to safely accommodate vulnerable users. Thus, vulnerable users such as pedestrians and bicyclists are expected to jointly use facilities that have constrained lateral offsets between the travel lanes and vulnerable user facilities such as sidewalks and multiuse paths. On many of these facilities, right of way (ROW), fiscal, or geographical constraints prohibit transportation agencies from increasing the offset distance.

Prior to the research conducted for this report, no positive barrier systems had been designed specifically for the purpose of providing positive protection between vulnerable user facilities and motorized facilities. To provide safe travel for vulnerable road users, state departments of transportation (DOTs) are implementing accommodations on the roadside. When enough ROW exists, DOTs increase the separation between pedestrians/bicyclists and the motor vehicle traffic. However, increasing this separation is not always an option. Therefore, DOTs are searching for effective means to provide positive protection and separation between pedestrian/bicycle and motor vehicle traffic.

A new, properly designed barrier could provide not only protection against errant motorists, but also a safer travel space for pedestrian and bicycle traffic. Typical roadside barriers incorporate concrete systems and post-and-beam guardrail barriers. Concrete barriers undergo no deflections upon motorized vehicle impact, representing the safest option to serve as a multifunctional barrier; however, their construction is cost prohibitive in many cases. Guardrail systems, though not as expensive as concrete barriers, might provide unacceptable lateral deflection, which would be hazardous for pedestrians and bicyclists. A commonly used post-and-beam system might also create tripping and snagging hazards for pedestrians and bicyclists.

Thus, a critical need exists to develop a new multifunctional barrier system that complies with the specific accommodation requirements of vehicles, pedestrians, and cyclists. This system should be affordable from the standpoint of constructability and installation, be appealing from an aesthetic perspective, consider adequate and proper sight distance, and be designed to safely contain direct hits from motorized users.

Under NCHRP Project 22-37, “Development of a MASH Barrier to Shield Pedestrians, Bicyclists, and Other Vulnerable Users from Motor Vehicles,” the research team developed a nonproprietary barrier for use in separating pedestrians, bicyclists, and other vulnerable users—including people who use a wheelchair and people who are blind or have low vision—from motor vehicles. Simulation models and full-scale crash tests were conducted, and the barrier met the requirements of the AASHTO Manual for Assessing Safety Hardware (MASH) (1) for Test Level 3 (TL-3) (high speed).

The barrier is appropriate for a variety of contexts, such as where ROW constraints reduce lateral offset between a roadway and a shared-use path. However, state DOTs might be unable to implement the new system until a transition system that connects the new barrier to a typical guardrail installation is designed and evaluated. Therefore, as part of the project, the research team also proposed a design of a transition system. The crashworthiness of the proposed design was preliminarily evaluated through finite element (FE) computer simulations to determine needed design modifications and to identify critical impact locations for vehicular testing. On the basis of the simulation results, MASH Tests 3-20 and 3-21 were conducted on the final transition design by impacting at each critical impact point.

This report presents details on the tasks completed to meet the objectives of this project. Chapter 2 provides a review of U.S. and international literature on roadside safety devices and corresponding design for vulnerable road users to highlight the current state of roadside safety.

In addition to the literature review, the research team conducted an agency survey to collect information on (a) projects/design contexts in which a barrier to separate vulnerable users from motor vehicles is needed; (b) existing standard drawings of a barrier to separate vulnerable users from motor vehicles; (c) implemented retrofit options of an existing barrier to separate vulnerable users from motor vehicles; and (d) preferences in terms of barrier design options. Chapter 3 describes the survey designed to solicit information from transportation agencies and design consultants and presents the findings.

On the basis of the results of the literature review and survey, the research team developed six preliminary barrier designs to address and balance system needs from the perspective of both vehicular impact performance and pedestrian/bicyclist accessibility; this information is presented in Chapter 4. The anticipated advantages and disadvantages of each design alternative, along with the perceived performance benefits and application limitations, are included.

Chapter 5 summarizes modeling done with LS-PrePost, including calibration of the newly developed model, to verify whether the system would behave realistically. The results obtained from the calibration models are compared with actual crash tests from the past.

Chapter 6 then provides details about the modifications made to the FE model described in Chapter 5 to optimize the model and make it more realistic. Using LS-DYNA, the researchers investigated the crashworthiness and critical impact point for the proposed multifunctional barrier design according to MASH TL-3 criteria.

Chapters 7 through 9 present details on the MASH testing and evaluation plan for the proposed multifunctional barrier system. The construction materials, test requirements, and test conditions are included.

Chapters 10 and 11 then summarize the full-scale crash tests conducted in accordance with MASH Tests 3-10 [passenger car, 62 miles per hour (mi/h), 25-degree (deg) orientation angle] and 3-11 (pickup truck, 62 mi/h, 25-deg orientation angle), respectively.

Next, Chapters 12 and 13 describe the transition system that was developed to connect the proposed multifunctional barrier system to a typical guardrail system. The two transition designs were (a) utilizing a W-beam transition system with additional rub rail and (b) a Thrie beam transition system. Using LS-PrePost, the researchers developed an FE transition model and investigated its crashworthiness according to MASH TL-3 criteria.

Chapters 14 and 15 then describe full-scale test plans for the proposed Thrie beam transition system, and Chapters 16 and 17 summarize the crash tests conducted according to MASH Tests 3-20 (passenger car, 62 mi/h, 25-deg orientation angle) and 3-21 (pickup truck, 62 mi/h, 25-deg orientation angle), respectively, including the test results. Finally, Chapter 18 presents the conclusions on the recommended multifunctional barrier and transition system and offers suggestions for future research.