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U.S. Department of Transportation U.S. Department of Transportation Icon United States Department of Transportation United States Department of Transportation

Public Roads - September/October 2014

September/October 2014
Issue No:
Vol. 78 No. 2
Publication Number:
Table of Contents

Communication Product Updates

Communication Product Updates

Below are brief descriptions of communications products recently developed by the Federal Highway Administration’s (FHWA) Office of Research, Development, and Technology. All of the reports are or will soon be available from the National Technical Information Service (NTIS). In some cases, limited copies of the communications products are available from FHWA’s Research and Technology (R&T) Product Distribution Center (PDC).

When ordering from NTIS, include the NTIS publication number (PB number) and the publication title. You also may visit the NTIS Web site at to order publications online. Call NTIS for current prices. For customers outside the United States, Canada, and Mexico, the cost is usually double the listed price. Address requests to:

National Technical Information Service
5301 Shawnee Road
Alexandria, VA 22312
Telephone: 703–605–6000
Toll-free number: 1–888–584–8332
Web site:

Requests for items available from the R&T Product Distribution Center should be addressed to:

R&T Product Distribution Center
Szanca Solutions/FHWA PDC
13710 Dunnings Highway
Claysburg, PA 16625
Telephone: 814–239–1160
Fax: 814–239–2156

For more information on R&T communications products available from FHWA, visit FHWA’s Web site at, the FHWA Research Library at (or email, or the National Transportation Library at (or email


Guidance on the Level of Effort Required to Conduct Traffic Analysis Using Microsimulation (Report)

Publication Number: FHWA-HRT-13-026


State and local agencies face many challenges in making decisions on transportation improvement projects. Traffic analyses are critical, yet analysts and modeling managers might not be aware of which analysis tools to use or the level of effort needed to obtain quality output. Consequently, agencies might not fund these projects sufficiently, leading to delays, cost overruns, or solutions that prove ineffective — or even a worsening of the problem the project was meant to correct.

This report offers guidance to help analysts and modeling managers apply traffic simulation analyses successfully. The document presents systematic ways to determine the appropriate scope and budget for traffic analysis efforts using microsimulation, which can help improve project and program decisions on transportation projects.

Researchers studied traffic analysis for geometric and operational design projects during a typical day (without unusual traffic situations, such as might occur on weekends, during summer vacation, or during a construction project). The study identified best practices and ways to tailor the level of effort needed for the analysis. For example, the number of intersections and parallel arterials in the network has a major impact on the level of effort required for model calibration and application. For more complex situations, such as where route choice or mode shift need to be considered, the researchers suggest using reported labor-hour estimates as a point of reference to apply to projects for determining level of effort.

Projects that appear similar may demand different levels of effort for numerous reasons, including the experience of project managers, analysts, and reviewers; the project’s purpose, objectives, and scope; the availability of sound data for model calibration; the number and complexity of the alternatives being analyzed; the number and effectiveness of project reviews conducted; and the amount of stakeholder involvement.

This report is consistent with the seven-step process outlined in Traffic Analysis Toolbox Volume III: Guidelines for Applying Traffic Microsimulation Modeling Software (FHWA-HRT-04-040). It is available to download at Printed copies are available from the PDC.


A Guide for Maintaining Pedestrian Facilities For Enhanced Safety (Report)

Publication Number: FHWA-SA-13-037


Each year, more than 4,000 pedestrians are killed and tens of thousands are injured in the United States. Research has demonstrated that pedestrian safety increases when facilities for walking, such as sidewalks, walkways, and curb ramps are implemented and maintained properly. However, maintaining pedestrian facilities so they remain safe and accessible is often a difficult undertaking, due to limited staffing and budgets. State and local agencies also face liability consequences related to poor, inadequate, or infrequent inspection and maintenance of pedestrian facilities. This report aims to identify barriers to as well as effective and exceptional practices for maintaining pedestrian facilities, with the ultimate goal of helping improve safety and mobility.

Researchers define maintenance as inspecting, preserving, repairing, and restoring a pedestrian facility for safe, convenient, and accessible use. The work may involve activities such as repairing surface defects or removing snow and ice, debris, and vegetation. This guide covers several categories of pedestrian facilities, including sidewalks, shared-use paths, crosswalks, other treatments of facilities for crossing streets, and pedestrian signs.

Safety specialists recommend that communities establish plans for maintaining pedestrian facilities. Prioritization and funding are often key aspects of a successful plan. A clear policy on how to schedule and fund facilities can help ensure timely maintenance and repair. The guidelines also suggest including inspection criteria and procedures in community plans. Considerations also might include who will inspect problems and when and how the inspections will take place — such as on a scheduled basis, in response to problems, or during street work or tree trimming.

This guide is the first of its type to research maintenance practices for pedestrian facilities nationwide and suggest recommended practices based on the findings. The guidance in this document addresses needs for facility maintenance, common issues, and inspection, accessibility, and compliance. Maintenance measures, funding, and construction techniques to reduce future maintenance are also discussed.

The guide is available for download at Printed copies are available from FHWA’s Office of Safety.


Safety Effects of Horizontal Curve and Grade Combinations on Rural Two-Lane Highways

Publication Number: FHWA-HRT-13-077


The safety effects of horizontal curves and grades on highways have been quantified separately, but experts do not currently know whether and how the safety performance of horizontal curves and grades interact together. This report discusses research undertaken as part of FHWA’s Highway Safety Information System (HSIS) contract to investigate these issues and provide results in a form useful to highway designers and safety engineers. The research objective was to quantify the safety effects of horizontal and vertical alignment combinations for incorporation into the American Association of State Highway and Transportation Officials’ (AASHTO) Highway Safety Manual (HSM).

This report reviews the existing state of knowledge about the safety effects of horizontal curves and grades, describes the HSIS data used for analysis, and discusses the statistical analysis approach. The research is based on HSIS data for Washington State and includes crash records from 2003 to 2008. The report presents the results of the safety analysis, details how crash modification factors are derived, and presents conclusions and recommendations. Researchers found that only rural two-lane highways had sufficient data for which modeling efforts appeared promising. The outcome was a set of safety prediction models for crashes involving fatalities, injuries, and property damage only.

The document is available to download at Printed copies are available from the PDC.


Lightweight Concrete: Development of Mild Steel in Tension (TechBrief)

Publication Number: FHWA-HRT-14-030


Much of the foundation for the current provisions for lightweight concrete in the AASHTO Load and Resistance Factor Design (LRFD) Bridge Design Specifications is based on research from the 1960s. However, over the past 50 years, broad-based advancements in concrete technology have enabled significant progress in the mechanical and durability performance of lightweight concrete.

Researchers at FHWA’s Turner-Fairbank Highway Research Center recently investigated the performance of lightweight concrete, including traditional mixes of coarse aggregate, fine aggregate, portland cement, and water. The mixtures studied included those with concrete compressive strengths ranging from 6,000 to 10,000 pounds per square inch (41 to 69 megapascals) and equilibrium densities between 125 and 135 pounds per cubic foot (2,000 to 2,160 kilograms per cubic meter). The study tested 27 precast/prestressed girders made of lightweight concrete mixed with three different lightweight aggregates representative of those available in North America. Researchers also tested 40 mild steel reinforced beams.

The study focused on the structural behavior of the concrete and assessed the compressive strength and other characteristics. The goal of this research is to recommend changes to the AASHTO LRFD Bridge Design Specifications for lightweight concrete, including a new definition of lightweight concrete to expand the range of unit weights and eliminate the definitions for terms relating to the constituent materials in the concrete.

This document discusses research that includes a significant number of bond strength tests on lightweight concrete. Results from this study are included in a database that covers a broad range of unit weights in order to determine trends for lightweight concrete as a function of unit weight. The database consists of data from 474 tests on lightweight concrete and normal-weight concrete.

The researchers present potential revisions to the AASHTO LRFD Bridge Design Specifications. These include a modification factor for lightweight concrete based on unit weight.

This technical brief is available to download at