Porous Friction Course (PFC) mixtures are designed with an open aggregate structure to yield high inplace air voids (i.e., typically between 15 and 20 percent). This allows rainwater to drain horizontally through the layer toward the edge of the pavement structure, thereby improving pavement surface friction. The TRB National Cooperative Highway Research Program's NCHRP Web-Only Document 305: Validation of a Performance-Based Mix Design Method for Porous Friction Courses is designed to assist state highw...

Guardrails are an important feature of the roadside that are used to shield errant motorists from becoming involved in even more catastrophic crashes by redirecting vehicles away from fixed hazards such as trees and poles and terrain hazards such as steep roadside slopes and fill embankments. The TRB National Cooperative Highway Research Program's NCHRP Web-Only Document 304: Criteria for Restoration of Longitudinal Barriers, Phase II develops a Field Guide to assist maintenance personnel in making decis...

The Moving Ahead for Progress in the 21st Century Act (MAP-21) requires a set of performance metrics to include assessment of serious injuries in crashes. The TRB National Cooperative Highway Research Program's NCHRP Web-Only Document 302: Development of a Comprehensive Approach for Serious Traffic Crash Injury Measurement and Reporting Systems presents a roadmap for states to develop comprehensive crash-related data linkage systems, with special attention to measuring serious injuries in crashes.

Hydroplaning is a serious problem that is associated with a relatively small but significant number of crashes. Statistics from various parts of the world indicate that approximately 15% to 20% of all road traffic crashes occur in wet weather conditions. The TRB National Cooperative Highway Research Program's NCHRP Web-Only Document 300: Guidance to Predict and Mitigate Dynamic Hydroplaning on Roadways provides a novel, transformational approach to estimate hydroplaning based on the physics behind it. Us...

A workshop, "Revised Contraction Scour Analysis," is presented in this training manual. The TRB National Cooperative Highway Research Program's NCHRP Web-Only Document 294: Revised Clear-Water and Live-Bed Contraction Scour Analysis Training Manual adheres to the guidance promulgated by the National Highway Institute and the International Association of Continuing Education and Training for adult learning. The document is supplemental to NCHRP Research Report 971:Revised Clear-Water and Live-Bed Contract...

The aging U.S. highway system, coupled with fiscal constraints, is placing increased pressures on highway agencies to maintain the highway system in a cost-effective manner and is, thus, creating greater needs for 3R projects. The TRB National Cooperative Highway Research Program's NCHRP Web-Only Document 244: Developing Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects presents the results of research to develop improved design guide...

Over the past 15 years, the nation’s transportation systems have experienced numerous significant disruptions that have resulted in economic loss and loss of human life. The 2020 COVID-19 pandemic is a recent example of how unexpected events can affect the performance and role of transportation systems. The TRB National Cooperative Highway Research Program's NCHRP Web-Only Document 293: Deploying Transportation Resilience Practices in State DOTs  examines the concept of transportation system resilie...

Several controlled laboratory studies have shown that air voids (AV) can have a large effect on the performance of asphalt pavements. AVs that are either too high or too low can cause a reduction in pavement life. The TRB National Cooperative Highway Research Program's NCHRP Web-Only Document 299: Investigating the Relationship of As-Constructed Asphalt Pavement Air Voids to Pavement Performance determines the effect of in-place AVs on the performance of asphalt concrete (AC) pavements. The document also...

Several types of speed limits exist, including statutory speed limit, posted speed limit, school zone speed limit, work zone speed limit, variable speed limit, and advisory speed. The TRB National Cooperative Highway Research Program's NCHRP Web-Only Document 291: Development of a Posted Speed Limit Setting Procedure and Tool documents the research efforts and findings from an NCHRP Project 17-76 to identify factors that influence a driver’s operating speed and the development of a Speed Limit Setting Pr...

The release of the Highway Safety Manual (HSM) by the American Association of State Highway and Transportation Officials (AASHTO) in 2010 was a landmark event in the practice of road safety analysis. Before it, the United States had no central repository for information about quantitative road safety analysis methodology. The TRB National Cooperative Highway Research Program's NCHRP Web-Only Document 295: Improved Prediction Models for Crash Types and Crash Severities describes efforts to develop improve...