Prior to 2013, the use of bicycle-specific signals in the U.S. was limited to a few jurisdictions. However, in recent years, the number of installations has grown rapidly. This research identified more than 500 intersections using bicycle signals in a variety of contexts. Despite the recent approval and practice, the TRB National Cooperative Highway Research Program's NCHRP Web-Only Document 273: Road User Understanding of Bicycle Signal Faces on Traffic Signals explores the questions that remain regardi...

The majority of instances of explicit consideration of service life design has been limited to signature bridges and other projects where extended service lives (in other words, greater than 100 years) are specified by the owner. Many state departments of transportation and other transportation agencies have recognized the importance of implementing service life design for typical highway bridges; however, no specification or standard has been developed to date in the U.S. The TRB National Cooperative Hi...

Over the past decade, significant state and federal resources have been expended to develop a state‐of-the-art set of reliability‐based bridge design and load rating specifications, including Load and Resistance Factor Design (LRFD) and Load and Resistance Factor Rating (LRFR). However, these design and rating methods were developed for larger bridge structures, and may result in overly conservative ratings when applied to buried culverts. Of the more than 600,000 records in the National Bridge Inventory...

There are several best management practices that are good at removing particulate-bound pollutants by settling, filtering, and, in the case of wetlands, settling, uptake, and incorporation of pollutants into biological matter (e.g., natural organic matter). However, a longstanding goal of stormwater treatment is the removal of the stormwater pollutant fraction that cannot be readily settled or filtered. While there are several media that may be employed to remove dissolved metals from stormwater, the med...

The performance of flexible and rigid pavements is known to be closely related to properties of the base, subbase, and/or subgrade. However, some recent research studies indicate that the performance predicted by this methodology shows a low sensitivity to the properties of underlying layers and does not always reflect the extent of the anticipated effect, so the procedures contained in the American Association of State Highway and Transportation Officials’ (AASHTO’s) design guidance need to be evaluated...

NCHRP Web-Only Document 261: Case Studies of Truck Activity Data for Emissions Modeling consists of seven case studies that are appendices A to G of NCHRP Report 909: Guide to Truck Activity Data for Emissions Modeling. NCHRP Research Report 909 explores methods, procedures, and data sets needed to capture commercial vehicle activity, vehicle characteristics, and operations to assist in estimating and forecasting criteria pollutants, air toxics, and greenhouse gas emissions from goods and services moveme...

TRB’s National Cooperative Highway Research Program (NCHRP) Web-Only Document 260: Proposed Refinements to Design Procedures for Geosynthetic Reinforced Soil (GRS) Structures in AASHTO LRFD Bridge Design Specifications explores the effect of adopting a closely‐spaced reinforcement layout in geosynthetic‐reinforced soil structures. While research since the early 1980s has identified the beneficial effect of closely‐spaced reinforcement in reinforced soil structures, such improvement in performance is not ...

TRB’s National Cooperative Highway Research Program (NCHRP) Web-Only Document 259: Guidelines to Improve the Quality of Element-Level Bridge Inspection Data is intended to assist inspectors in identifying defects and assigning the appropriate condition state for bridge elements. To ensure the safety and serviceability of bridges, the guidelines include accuracy requirements designed to help promote consistency in the collection of element-level data for bridges on the National Highway System. The quality...

TRB's National Cooperative Highway Research Program (NCHRP) Web-Only Document 258: Manual on Subsurface Investigations provides an update to the American Association of State Highway Transportation Officials (AASHTO) 1988 manual of the same name. This report reflects the changes in the approaches and methods used for geotechnical site characterization that the geotechnical community has developed and adopted in the past thirty years. The updated manual provides information and guidelines for planning and...

TRB’s National Cooperative Highway Research Program (NCHRP) Web-Only Document 256: Assessing Interactions Between Access Management Treatments and Multimodal Users describes operational and safety relationships between access management techniques and the automobile, pedestrian, bicycle, public transit, and truck modes. This contractor's report may help assist in the selection of alternative access management techniques based on the safety and operation performance of each affected travel mode.The r...