Transportation Intelligence

Volume 5 Number 5

October 2007

Structures

Safety

Geometric Design

Traffic Control

Pavements

Feedback

Structures
Corrosion inhibiting systems for concrete bridges - 10 years of field performance evaluation
The performance of nine corrosion-inhibiting systems for reinforced concrete structures exposed to the severe Canadian climate was assessed in the field on bridge barrier walls. These systems were composed of one or more of the following components: concrete admixtures, reinforcing steel coatings, and/or concrete surface coatings/sealers. The field evaluation consisted of annual corrosion surveys of half-cell potential and corrosion rate, as well as laboratory testing on concrete cores. After ten years, the main reinforcement at a depth of 75 mm was found in relatively good condition. Special bars embedded at a depth of 13-mm showed signs of advanced corrosion for all systems. Non-destructive corrosion evaluation of 25-mm deep special bars indicated lower risks of corrosion for corrosion-inhibiting systems composed of concrete admixtures. (National Research Council of Canada Institute for Research in Construction report NRCC-49207, June 2007, 11 p.)

Pavements
Long-Life Concrete Pavements in Europe and Canada
Long-life concrete pavements require less frequent repair and rehabilitation and contribute to highway safety and congestion mitigation. The Federal Highway Administration, American Association of State Highway and Transportation Officials, and National Cooperative Highway Research Program sponsored a scanning study to identify design philosophies, materials requirements, construction procedures, and maintenance strategies used in Europe and Canada to build long-life concrete pavements. (US Federal Highway Administration report FHWA-PL-07-027, August 2007, 80 p.)

Structures

Countermeasures to Protect Bridge Abutments from Scour
This report will be of interest to transportation departments that are responsible for constructing and maintaining bridges that span waterways. This report provides selection criteria and guidelines for the design and construction of countermeasures to protect bridge abutments and approach embankments from scour damage. The selection process identifies the countermeasure concepts that may be appropriate for addressing a scour concern, indicates possible construction options, and then provides design relationships associated with the layout and dimensioning of countermeasures developed in the course of this project. Guidelines are provided for the following abutment countermeasures: riprap, cable-tied blocks, geobags (permeable bags filled with gravel), parallel walls (guidebanks with no elliptical end), spur dikes located locally to the abutment, and abutment collars (a horizontal plate attached to the abutment). (TRB's National Cooperative Highway Research Program Report 587, 2007, 230 p.)

Risk-Based Management Guidelines for Scour at Bridges with Unknown Foundations
The US currently has over 60,000 bridges over water with unknown foundations. This report presents a risk-based approach to managing these bridges in the absence of foundation information. The general framework in this report, which is primarily applied to scour failure, can easily be applied to other hazards such as earthquakes and tsunamis. The guidelines illustrate how to collect appropriate data, estimate risk of failure from an estimated failure probability and associated economic losses, and use risk in a structured approach to select an appropriate management plan. Risk analysis is specifically used to select appropriate performance standards for various bridge classifications and justify the costs of nondestructive testing of foundations, monitoring activities, and countermeasures. The scour guidelines were then applied to sixty case studies in the US to validate the management plan that it selected for bridges with known foundations, and to illustrate its specific application in a variety of settings. (TRB’s National Cooperative Highway Research Program (NCHRP) Web-Only Document 107,October 2006, 458 p.)

Guidelines for Concrete Mixtures Containing Supplementary Cementitious Materials to Enhance Durability of Bridge Decks
This report is designed to help facilitate the use of supplementary cementitious materials to enhance durability of concrete used in highway construction, especially bridge decks. The report includes a methodology for selecting optimum concrete mixture proportions that focuses on durability aspects of concrete and the performance requirements for specific environmental conditions. The methodology is presented in a text format and as a computational tool, in the form of a Visual Basic–driven Microsoft Excel spreadsheet. Background information and a hypothetical case study was published as NCHRP Web-Only Document 110: Supplementary Cementitious Materials to Enhance Durability of Concrete Bridge Decks (http://www.trb.org/news/blurb_detail.asp?id=7715). The Statistical Experimental Design for Optimizing Concrete (SEDOC) (http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_566_SEDOC.zip), the computational tool for the concrete mixture optimization methodology, and the user’s guide (http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_566_Sedoc_UG.pdf) are available in a ZIP format for download. (TRB’s National Cooperative Highway Research Program (NCHRP) Report 566, 2007, 130 p.)

Durability of Segmental Retaining Wall Blocks: Final Report
Segmental retaining wall (SRW) systems are commonly and successfully used in a range of applications, including highway projects. The deterioration of some SRW installations in State highway agency (SHA) applications has resulted in concern over the long-term performance of SRW systems and has led to stricter specifications and, in some cases, restrictions on future use of SRW systems. In response to these concerns, a Federal Highway Administration (FHWA)-funded research project was initiated to determine the cause and extent of SRW block distress, to identify and recommend test methods for improving durability of SRW systems, and to recommend specifications for SHAs to ensure long-term durability and performance of SRW systems in highway applications. This report summarizes the key findings of this project and provides guidance on producing durable SRW blocks to ensure long-term performance of SRW systems in highway applications. (US Federal Highway Administration Report FHWA-HRT-07-021, April 2007, 271 p.)

Back to Top

Safety

Safe Road Shoulders
If a vehicle drives off the road, this does not have to be a problem if the vehicle stops in the shoulder or can be driven back onto the carriageway again. However, if there are trees or ditches close to the shoulder there is a very large risk of a shoulder crash. This fact sheet discusses the shoulder problems for a number of road types and deals with solutions, particularly for rural roads. (Netherlands SWOV Institute for Road Safety Research Fact Sheet, August 2007, 6 p.)

Safety Treatments at Isolated High-Speed Signalized Intersections: Synthesis
High-speed intersections pose a safety and operational challenge. Currently, no specific guidance for treating high-speed intersections exists, particularly in the case of intersections with substantial truck traffic. To fill in this gap, this paper presents a synthesis of findings from a literature review and a survey of practitioners. Results indicate that the primary safety concerns at high-speed intersections relate to red-light running and rear-end collisions. Further, operational and safety concerns at high-speed intersections were identified as being related to the different characteristics of trucks (e.g., accelerating/decelerating capabilities). The survey indicates no consensus among practitioners on how best to improve operations and safety at high-speed signalized intersections. Specific concerns over the liability and system/equipment reliability issues were raised. This note summarizes the findings from the literature review and survey and offers recommendations to increase awareness and acceptance for high-speed intersection treatments. (Journal of Transportation Engineering, September 2007, pp. 523-528.)(To obtain this article, please contact the TIS.)

Pedestrian Signal Safety for Older Persons
This study had two primary objectives: 1) to provide the supporting research to assist traffic engineers in understanding the walking characteristics of older pedestrians and 2) to provide more information on the extent to which various intersection operational conditions might be able to tolerate additional time for the pedestrian interval without sacrificing substantial efficiencies (and, conversely, the identification of intersection operational conditions that would provide significant degradation in the movement of vehicles). (AAA Foundation for Traffic Safety Report, July 2007, 238 p.)

Analysis of Bicycle-Related and Pedestrian-Related Roadway Crashes
The premise of this study is that crashes involving bicyclists and pedestrians are similar in characteristics, including type and cause. Using available data and existing analysis tools, the study conducted a corridor-specific approach along state highways within local and/or county jurisdictional boundaries to identify potential trends based on patterns in crash types and causes. By identifying common causal factors of bicycle and pedestrian crashes, this study should help planning and design efforts to provide safer intersections and corridors for use by pedestrians and bicyclists. The study developed recommendations to improve statewide, county and local data recording of bicycle and pedestrian crash factors. (Colorado Department of Transportation Report 2007-11, June 2007, 183 p.)

Building the Road Safety Profession in the Public Sector
This report examines the growing need for experts at all levels of government to develop and implement systems- and science-based approaches to road safety management. According to the committee that authored the report, the lack of professional recognition and comprehensive road safety education and training opportunities is threatening the ability of public agencies to build the knowledgeable and skilled road safety workforce that is needed to make safety advances. To address this need, the report recommends that the American Association of State Highway and Transportation Officials and the Governors Highway Safety Association forge a broad-based alliance of public, private, and educational organizations to champion the road safety profession. (Transportation Research Board Special Report 289, 2007, 84 p.)

Back to Top

Geometric Design

Rethinking Geometric Design Standards for Bike Paths
The “single file” and “side-by-side” travel characteristics of bicyclists and pedestrians should be considered for the determination of stopping sight distances, horizontal sightline offsets, and minimum lengths of vertical curves for bike paths. This paper describes these unique travel behaviors and classifies them into two cases (Case I and Case II) for geometric design. It presents a set of new design equations and charts that consider these two design cases and introduces design methods to supplement current AASHTO standards and guidelines. The paper then provides a practical procedure for using the new charts and equations for design of bike paths. (Journal of Transportation Engineering, September 2007, pp. 539-547.)(To obtain this article, please contact the TIS.)

Special Report: Accessible Public Rights-of-Way - Planning and Designing for Alterations
The Access Board is the Federal government's specialist in accessible design. Under the Americans with Disabilities Act (ADA), the Board is responsible for developing the minimum accessibility guidelines needed to measure compliance with ADA obligations when new construction and alterations projects are planned and engineered. This advisory compiles the recommendations of a subcommittee of PROWAAC that worked to develop and highlight model rights-of-way design alternatives, design processes for making alterations, design solutions to specific problems, and case studies demonstrating examples of accessible design practices from across the country. (Public Rights-of-Way Access Advisory Committee Report, July 2007, 116 p.)

Back to Top

Traffic Control

Temporary Traffic Control and Enforcement of Traffic Laws in Closed Road Sections
Public travel by motor vehicles is often necessary in road and street sections that have been officially closed for construction, repair, and/or other reasons. This authorization is permitted in order to provide access to homes and businesses located beyond the point of closure. The MUTCD does address appropriate use of specific regulatory signs at the entrance to closed sections; however, direct guidance for temporary traffic control measures within these areas is not included but may be needed. Interpretation and enforcement of common practices may vary among transportation agencies. Enforcement of traffic laws in closed road sections is desirable to maintain safety for workers and for specifically authorized road users. In addition, occasional unauthorized entry by motor vehicles is experienced in closed road areas causing property damage. Citations beyond simple trespass may be advisable to provide better security for construction sites, reduce economic losses from damage to completed work, and create safer work zones. (Center for Transportation Research and Education at Iowa State University Report 06-263, June 2007, 76 p.)

Communicating With the Public Using ATIS During Disasters: A Guide for Practitioners
Advanced Traveler Information Systems, ATIS, can play an important role in communicating essential information to the public during disasters. Variable message signs, 511 telephone systems, highway advisory radio, and websites are some of the dissemination devices of systems that collect, process, and disseminate information about travel conditions to the public for day-to-day transportation operations, and these same systems need to be effectively used during disaster situations. This document provides advice on use of ATIS during disasters and is intended not only for state and local transportation agencies but for their partners in public safety and emergency management agencies. It offers practical guidance to managers of transportation management centers and emergency operations and to public information officers who may be called on to staff joint information centers during disasters. (US Federal Highway Administration Report FHWA-HOP-07-068, April 2007, 36 p.)

Active Traffic Management: The Next Step in Congestion Management
The combination of continued travel growth and budget constraints makes it difficult for transportation agencies to provide sufficient roadway capacity in major metropolitan areas. The Federal Highway Administration, American Association of State Highway and Transportation Officials, and National Cooperative Highway Research Program sponsored a scanning study to examine congestion management programs and policies in Europe. The scan team observed that transportation agencies in Denmark, England, Germany, and the Netherlands, through the deployment of congestion management strategies, are able to optimize the investment in infrastructure to meet drivers' needs. (US Federal Highway Administration report FHWA-PL-07-012, March 2007, 84 p.)

Back to Top

Pavements

Guidelines for Evaluation of Existing Pavements for HMA Overlay
This report discusses the application of nondestructive test (NDT) tools for evaluating existing pavements for hot-mix asphalt (HMA) overlays.The NDT tools covered in this report include ground penetrating radar (GPR), falling weight deflectometer (FWD), and rolling dynamic deflectometer (RDD). The GPR is used to estimate the thickness of existing pavement layers, and identify section breaks and potential trapped moisture problems. The FWD is used to evaluate the structural capacity of the existing pavement, and the in-situ layer modulus can be backcalculated from FWD data. In addition, for existing concrete pavements, the FWD can be used to determine load transfer efficiency (LTE) at joints and/or cracks. The application of the RDD to evaluate existing concrete pavements is also discussed. Finally, general guidelines for evaluating existing pavements for HMA overlays are proposed in this report. (Texas Transportation Institute Report 0-5123-2, May 2007, 110 p.)

Precast Concrete Panel Systems for Full-Depth Pavement Repairs Field Trials
The use of precast slabs as an alternative to conventional cast-in-place repairs may be an effective means of reducing construction time, thereby minimizing user delay and travel costs while obtaining a long-lasting, durable repair. This report summarizes the 3-year study, “Field Trials of Concrete Pavement Product and Process Technology—Precast Concrete System for Rapid Repairs,” in which precast slabs were used for joint repair and slab replacement on in-service Michigan and Colorado highways. Cast-in-place, full-depth patches were installed as controls. The report contains a summary of the relevant literature; summaries of the field trials and their findings regarding efficiency and durability; recommendations for precast panel installation; a sample distress documentation report; a presentation of construction guidelines; and a sample special provision specification developed as part of the study. (US Federal Highway Administration report FHWA-HIF-07-019, February 2007, 84 p.)

Experimental Assessment of Aggregate Surfacing Materials
An extensive suite of geotechnical laboratory tests were conducted to quantify differences in engineering properties of three crushed aggregates commonly used on Montana highway projects. The material types are identified in the Montana Supplemental Specifications as CBC-6A, CBC-5A, and CTS-2A. Drainage capacity was quantified by conducting multiple saturated constant head permeability tests on 10-inch-diameter samples of each material type. The CBC-6A and CTS-2A materials had the highest average permeability values, while the CBC-5A materials had the lowest. Permeability was shown to depend more on the fine fraction void ratio (ef) than on aggregate type or maximum particle size. An analytical method of predicting permeability based on ef was developed, which will allow MDT designers to estimate permeability based on gradation and state of compaction. (Montana Department of Transportation Report FHWA/MT-07-011/8117-30, July 2007, 77 p.)

Back to Top