Book Description

Work zones often require the use of temporary concrete barriers (TCBs) within a limited area to provide protection for construction workers. In situations where an existing guardrail is immediately adjacent to the construction hazards that need to be shielded, highway designers must either connect the guardrail to the temporary barrier or replace it with TCB. Although interconnecting the two barrier systems represents the more convenient option, at present no suitable solutions have been made available. A transition from guardrail to temporary barriers may not need to be nearly as stiff as a conventional approach transitions. However, it must provide sufficient stiffness and strength to prevent pocketing as well as to shield the end of the concrete barrier to prevent serious wheel snag. In addition, considerations must be made for transitioning from the TCB to the guardrail, anchoring the TCB system, and the potential use of tie-downs to limit TCB deflection. TCBs are connected and transitioned to many types of barriers. Unfortunately, little effort has been devoted to this issue. The only transitions previously developed have been between TCBs and safety shaped concrete barriers and TCBs and permanent concrete median barriers. Transitions between TCBs and other common barrier types, such as guardrail, have typically not been full-scale crash tested and may pose a serious hazard to motorists during an impact. Transitions between two barrier types generally are designed with the assumption that it is more critical to transition from a less stiff barrier to a stiffer barrier due to concerns for pocketing and snag on the stiffer barrier system. However, in the case of a TCB system, design of the transition can be more complex. Design of a transition between TCB and guardrail must consider several factors: (1) Connection of the guardrail on the upstream or downstream end of the TCB system - The location of the guardrail on either the upstream or downstream end of the transition will largely affect the transition along with other factors. For example, the attachment of the guardrail to the downstream end of an unanchored, free-standing TCB system would require a transition. This could be as simple as using tie-down anchorages on the TCB segments to increase their stiffness prior to the guardrail attachment. Conversely, attachment of the guardrail to the upstream end of a free-standing, TCB system would require a transition as well. However, this type of transition would require stiffening the guardrail as it approached the TCB. (2) Anchorage of the end of the TCB system - The location and design of the end anchorage for the TCB system will largely determine the stiffness of the TCB end as compared to the guardrail as well as the transition configuration. (3) Free-standing barrier vs. tie-down anchorage - The stiffness of the TCB section varies depending on whether the barrier segments use any form of tie-down anchorage. The design of the transition between the rail and the TCB would change depending on whether the barrier segments were free-standing or anchored. (4) Direction of traffic - The transition design may depend on the potential for two-way traffic or reverse impacts. Due to the wide range of factors affecting the design of a TCB to guardrail transition, it is necessary to develop a better understanding of the most common and most critical transition installations. Then, a transition design could be developed to meet those needs. It is anticipated that this transition design would be developed around the F-shape, TCB segment and the recently developed Midwest Guardrail System (MGS). The research study recommended herein would primarily be directed toward improving the safety and minimizing risk for the motoring public traveling within our nation's work-zones and on our highways and roadways. More specifically, this project would address the goal of the Smart Work Zone Deployment Initiative, which is "to develop improved methods and products for addressing safety and mobility in work zones by evaluating new technologies and methods, thereby enhancing safety and efficiency of traffic operations and highway workers. The project is a public/private partnership between the sponsoring public transportation agencies in several Midwestern States, the Federal Highway Administration (FHWA), private technology providers and university transportation researchers." The overall objective of this research effort is to develop a MASH TL-3 transition design between TCBs and the MGS. The design of the transition would focus on a representative selection of state departments of transportation (DOTs) highest priority configuration. Due to the large number of unknowns, this phase of the project will focus on the development of design concepts for the highest priority transition need. Full-scale crash testing of the proposed transition design is not a part of this project and may be performed in a future phase of the project. This research effort will begin with identifying and quantifying the most pressing TCB to guardrail transition needs. Although a need to develop configurations for most, if not all, of the TCB to guardrail transition needs may exist, this project will address the highest priority need. Thus, the state DOTs of the Midwest States Pooled Fund Program will be surveyed to identify the highest priority TCB to guardrail transition need. After the critical transition need is identified, potential transition concepts and prototype designs will be brainstormed. Computer simulations with LS-DYNA, a non-linear explicit finite element code, will be used to investigate and evaluate the concepts and prototype designs. CAD details for the proposed transition design will be prepared. A summary report detailing the research effort will be compiled and will include recommendations for future full-scale crash testing of the TCB to guardrail transition as well as recommendations for further development of TCB to guardrail transitions. The research study is directed toward improving the safety by minimizing the risk for the motoring public traveling within our nation's work-zones and on our highways and roadways. Since W-beam guardrail has proven to provide better safety performance than temporary concrete barriers, the development of an effective transition between the two can help preserve guardrails outside the immediate work-zone area, thus providing an overall higher level of safety for motorists. The new transition would also eliminate the use of an unproven connection between guardrail and temporary barriers. Further, limiting the use of temporary concrete barriers strictly to the work zone area will also minimize the traffic disruption that these barriers can create to motorists passing in work zones. Following the development efforts, a research report will be prepared that summarizes the results of the study. If warranted, a formal paper will be prepared and submitted for publication in a refereed journal, such as a Transportation Research Record, so that dissemination and distribution of the final research results will provide the most significant impact in terms of safety benefit for the motoring public