NCHRP Report 

About: NCHRP Report is an academic journal. The journal publishes majorly in the area(s): Transportation planning & Strategic planning. It has an ISSN identifier of 0077-5614. Over the lifetime, 617 publications have been published receiving 21984 citations.

Recommended procedures for the safety performance evaluation of highway features

Abstract: Procedures are presented for conducting vehicle-crash tests and in-service evaluation of roadside safety features or appurtenances including (1) longitudinal barriers such as bridge rails, guardrails, median barriers, transitions, and terminals; (2) crash cushions; (3) breakaway or yielding supports for signs and luminaires; (4) breakaway utility poles; (5) truck-mounted attenuators; and (6) work zone traffic control devices. The purpose of the procedures is to promote the uniform testing and in-service evaluation of roadside safety features so that highway engineers may confidently compare the safety performance of designs that are tested and evaluated by different agencies. Standardized procedures are presented for the testing and evaluation of features under severe vehicle impact conditions rather than to typical or average highway situations. This report represents a comprehensive update of the procedures for safety performance evaluation described in NCHRP Report 230. The evolution of roadside safety concepts, technology, and practices, significant changes in the vehicle fleet, the emergence of many new barrier designs, increased interest in matching safety performance to levels of roadway utilization, new policies requiring the use of safety belts, and advances in computer simulation and other evaluation methods necessitated an update. The report differs in the following ways: (1) It is presented as an all metric document; (2) It provides procedures for the testing of a wider range of barriers, terminals, crash cushions, breakaway support structures and utility poles, truck-mounted attenuators, and work zone traffic control devices; (3) It uses a 3/4-ton pickup truck as the standard test vehicle in place of the 4500-lb passenger car; (4) It defines other supplemental test vehicles including a mini-compact passenger car (700 kg), single-unit cargo trucks (8000 kg), and tractor/trailer vehicles (36,000 kg) to provide the basis for optional testing to meet higher performance levels; (5) It includes a broader range of tests for each category of device to provide a uniform basis for establishing warrants for the application of roadside safety hardware considering the levels of utilization of the roadway facility; (6) it includes guidelines for the selection of the critical impact point for crash tests on redirecting-type safety hardware; (7) It provides information related to enhanced measurement techniques related to occupant risk; (8) It retains the three basic evaluation criteria, but alters the limiting values for acceptance; (9) It reflects a critical review of other methods and technologies for safety-performance evaluation, such as surrogate test vehicles and computer simulations, and incorporates state-of-the-art methods in the procedures; and (10) It provides optional criteria for side-impact testing. The evolution of the knowledge of roadside safety and performance evaluations is reflected in this document.

Simple performance test for superpave mix design

Abstract: This report presents the findings of a research task to identify a simple test for confirming key performance characteristics of Superpave volumetric mix designs. In this initial phase of the work, candidate tests for permanent deformation, fatigue cracking, and low-temperature cracking were identified and recommended for field validation in the next phase of work. The report will be of particular interest to materials engineers in state highway agencies, as well as to materials suppliers and paving contractor personnel responsible for design and production of hot mix asphalt.

Characterization of modified asphalt binders in superpave mix design

Abstract: This report documents the results of a study on the applicability of Superpave specification (AASHTO MP1, "Standard Specification for Performance Graded Asphalt Binder") and protocols developed for asphalt cements to modified asphalt binders. A survey indicated that, although the majority of state agencies intend to increase future use of modified binders, very little is known about the binders' behavior. In addition, there are serious concerns regarding their storage stability, aging, and mixing and compaction temperatures. Using advanced rheological characterization of a selected set of binders and mixtures, it was found that the binder specification parameters in the current AASHTO MP1 are not adequate to rank the modified binders according to their contribution to mixture damage. The concepts of viscous flow and energy dissipation were explored in an effort to derive binder parameters that more effectively relate binder to mixture behavior. Suggested test protocols and specification parameters were developed to integrate the new concepts into a future specification. A direct measure of the glass transition behavior and the use of a design-cooling rate were identified as reliable estimators of the binders' role in thermal cracking. Also, a storage stability test and a particulate additive test were developed and proposed as standard tests. The concept of low shear viscosity was introduced for the determination of laboratory mixing and compaction temperatures to avoid excessive heating and to consider the shear-rate dependency of modified binders. Revisions to the binder grading system are recommended to include a three-level grading scheme. A field validation plan is proposed to test the validity of these concepts and to derive reliable specification criteria and limits.

Recommended use of reclaimed asphalt pavement in the Superpave mix design method: technician's manual.

Abstract: This is a technician's manual for use of reclaimed asphalt pavement (RAP) in Superpave-designed hot mix asphalt (HMA). It will be of particular interest to materials engineers in state highway agencies and to contractor personnel responsible for designing HMA according to the current Superpave method.

Valuation of travel-time savings and predictability in congested conditions for highway user-cost estimation

Abstract: This report contains the findings of a study to develop methodologies for measuring the effects of congestion on the values highway users place on travel-time savings and predictability. The methodologies were used to generate values for factors for different degrees of congestion. The study also defines an approach for incorporating these factors in highway user-cost estimates. The contents of this report, therefore, will be of immediate interest to highway professionals responsible for planning, administering, and financing highway improvements, as well as those involved in highway operations, capacity, and traffic control. The report also will be of interest to those concerned with freight transportation issues as well as environmental, safety, and human performance issues.