Hot Topics is our electronic newsletter highlighting new publications and resources from a variety of sources.
Sealed with a chip: best practices for
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
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
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.
It's recycling day: don't forget your
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 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.
Red alert: report examines safety impacts
of red-light cameras
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.
Get smart: report shares "smart growth" strategies
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:
- Why is smart growth a transportation issue?
- What does a smart growth transportation system look like?
- How does smart growth differ with location (urban infill, suburban
redevelopment, and fringe growth)? How do institutional arrangements
vary by location?
- Who must be involved to achieve a smart growth transportation
system, and what institutional obstacles exist?
- How can transportation agencies support smart growth? What
are the available tools?
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.
New Web site assists with growth planning
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.
The great infrastructure get-together:
Intertraffic conference & trade fair
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
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.