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A chip seal (also called a "Seal Coat") is essentially a single layer of asphalt binder that is covered by embedded aggregate (one stone thick). Its primary purpose is to seal
the fine cracks in the underlying pavement's surface and prevent water intrusion into the base and subgrade. The aggregate protects the asphalt layer from damage and helps create a skid-resistant surface for vehicles.
Many agencies base their chip seal procedures on local experience rather than
on engineering principles, and they have limited knowledge of what other agencies may be doing. A new synthesis by the TRB's National Cooperative Highway Research Program (NCHRP)— Synthesis 342: Chip Seal Best Practices—summarizes information on good practices for materials, design, construction techniques, and effectiveness of chip seals.
The report identifies the benefits of using chip seal as part of a preventative maintenance program and highlights advanced chip seal programs in use around the world. It includes approximately 40 best practices in the areas of chip seal design methods, contract administration, equipment practices, construction practices, and performance measures.
Early uses of chip seal were predominantly as wearing courses in the construction of low-volume gravel roads, but in the past 75 years, chip seals have evolved into maintenance treatments that can be successful on both low-volume and high-volume pavements. The popularity of chip seals is a direct result of their low initial costs in comparison with those of thin asphalt overlays and other factors influencing treatment selection.
To view the report online or to order a copy, go to www.trb.org/news/blurb_detail.asp?id=4901.
The pace of highway, bridge, and building construction has steadily picked up over the past century, and by now many older facilities need to be repaired or replaced. These facts mean two things: first, the demand for construction aggregates keeps growing, and second, the amount of construction waste is increasing. Two billion tons of aggregate are produced each year in the United States, and production is expected to increase to more than 2.5 billion tons per year by 2020, raising concerns about the availability of natural aggregates.
The most common way to dispose of construction waste has been in landfills. As cost, environmental regulations, and land use policies for landfills become more restrictive, alternative uses of the waste are needed. This situation has led state agencies and the aggregate industry to begin recycling concrete debris as an alternative aggregate.
To capture the most advanced uses of recycled concrete aggregate (RCA) for transportation uses in the country, the Federal Highway Administration has published Transportation Applications of Recycled Concrete Aggregate (FHWA-IF-05-013). The report summarizes information collected during the review of practices in five states: Minnesota, Texas, Virginia, Michigan, and California. These states were selected based on their level of use and supply generated of RCA as an aggregate, as well as to obtain a cross-section of the country.
The report identifies applications where the use of RCA can have engineering, economic, and environmental advantages; the barriers related to these RCA applications; and the best practices that allowed state transportation agencies, recycled concrete producers, and contractors to overcome these barriers. It provides recommendations, guidelines, and specifications for furthering the use of RCA more widely throughout the country.
The overall findings of the review team were that RCA is a valuable resource, and by proper engineering it can be used for PCC pavement, aggregate base, and miscellaneous uses.
Whether urban or rural, intersections just aren't the safest places to be. About 1,000 people die each year in roughly 100,000 crashes at U.S. intersections. A new way to help reduce these numbers—the use of red-light cameras (RLC)—is becoming more common, including several new installations in Minneapolis. The effectiveness and benefits of the RLC systems, however, have been unclear.
To estimate the crash and associated economic effects of RLC systems, the Federal Highway Administration conducted a before-and-after evaluation using data from seven jurisdictions across the country. The study derived rear-end and right-angle unit crash costs for various severity levels at 132 treatment sites.
Consistent with many previous studies, the evaluation found the number of right-angle crashes fell with RLCs—but the number of rear-enders rose. Still, even though the negative effects of increased rear-end crashes partially offset the positive effects on right-angle crashes, there is an economic benefit between $39,000 and $50,000 per treated site per year.
Even if modest, this economic benefit is important, the report says. In many instances today, the RLC systems pay for themselves through collected fines. This differs from most safety treatments in many jurisdictions where installation, maintenance, and other costs must be weighed against treatment benefits.
The benefit per site can be increased by careful site selection. RLC systems should be considered for intersections where there are relatively few rear-end crashes and many right-angle ones, a higher proportion of entering traffic on the major road, shorter cycle lengths and intergreen periods, and one or more left-turn protected phases. The analysis also revealed that high publicity about the systems and warning signs at both RLC intersections and city limits will enhance system benefits.
The executive summary of the research—Publication No. FHWA-HRT-05-049—is available at www.tfhrc.gov/safety/pubs/05049. A PDF of the full report, Safety Evaluation of Red-Light Cameras (FHWA-HRT-05-048, 149 KB), published by the Federal Highway Administration in April 2005, may be downloaded from that site as well.
Many communities and citizens are interested in "smart growth" strategies. But what exactly is smart growth—stopping a new strip mall, or restricting development to certain areas? Other questions about smart growth include its impact on travel patterns, the public's interest, and feasibility.
Despite continuing debates about such questions, the public and decision makers are calling for transportation projects and plans to support smart growth. Transportation professionals and the agencies they work for are trying to respond. To do so, they must identify the characteristics of transportation systems that support smart growth, and then determine how to provide such systems while achieving their traditional goals.
Two Transportation Research Board (TRB) committees collaborated last year to organize a conference on how transportation professionals can do so. The conference—"Providing a Transportation System to Support Smart Growth: Issues, Practice, and Implementation"—addressed the following questions:
The "how" session focused on the practical topic of available tools, such as traffic calming, transit service design, highway design, access management, and planning for community bypasses. Examples of tools were found in rural areas, small towns, suburban communities, urban areas, and reclaimed industrial areas.
One central theme ran through all the presentations: the importance of working with the community to design transportation improvements.
The TRB has published the conference proceedings, titled Smart Growth and Transportation: Issues and Lessons Learned. It is online at http://trb.org/publications/conf/CP32smartgrowth.pdf.
The Federal Highway Administration has launched a new Web site with information on the use of scenario planning as a tool to help communities plan for growth. Scenario planning provides a framework for developing a shared vision for the future by analyzing various factors that affect growth, such as health, transportation, economic, environmental, and land use. Such planning efforts may be done on a statewide level or for metropolitan regions.
The new site provides a range of resources to encourage the use of scenario planning, including background, noteworthy practices, resources, and contacts. It also provides links to reports from scenario planning workshops held in 2004 in New York, Rhode Island, Hawaii, and Florida. The new site is at www.fhwa.dot.gov/planning/scenplan/index.htm.
For the first time in its 32-year history, the annual Intertraffic international trade fair will be held in North America. Last year's fair drew more than 650 exhibitors and 24,000 (yes, thousand) participants in Amsterdam.
Intertraffic North America (INA), September 27–29, 2005, in Baltimore, will not be that large, but the organizers—the American Road & Transportation Builders Association (ARTBA) and Amsterdam RAI—do expect a strong turnout.
INA will have a wide range of session topics providing something of interest for counties, cities, DOTs, consultants, and contractors. Combining a major exhibition with a comprehensive conference, INA will discuss cutting-edge issues of interest to the transportation infrastructure industry plus provide professional development hours for people who need to maintain their engineer's certification.
The exhibition will bring together 200 companies promoting their latest products and services for the transportation infrastructure market at one location. Firms will represent virtually every aspect of transportation infrastructure: road infrastructure, parking road safety, traffic management, and consultancy and services.
INA has been endorsed by the National Association of County Engineers (NACE) and the National Local Technical Assistance Program Association, and is being held in partnership with the Federal Highway Administration.
To learn more about it, visit www.northamerica.intertraffic.com.
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