(published in the Salt Institute's Fall 2001 Salt and Highway Deicing newsletter)
If you ask this question concerning the use of sand to any highway
agency or public works person, you will probably get a different answer from each person. Most snowfighters have some experience with using
sand or abrasives (we’ll use “sand” to encompass both in this article, but
abrasives can be natural silica or man made cinders, incinerator ash, etc.). The range of opinions on using sand is at least as
broad as Snowfighting agencies’ different operating conditions, materials costs and
local political considerations.
Sand may be justified when temperatures are too extreme for normal
snowfighting and agencies need to provide a temporary increase surface friction to
maintain the safest possible roadway conditions, particularly at intersections, bridges or
overpasses. Over the last five years,
however, research on the use of abrasives has documented harm to humans and the
environment as well as defined the limited safety effectiveness of sand as a snowfighting
tool.
The biggest limitation of sand, of course, is that it has no melting
action – it does not melt snow or ice. Road
users, the customers of transportation agencies, have expectations for winter maintenance
levels-of-service. Most want bare pavement
preserved or restored as quickly as possible. Some
storms make this physically impossible. Some
climates make bare pavement fiscally impossible. Agencies
then turn to applying sand for traction as a last resort.
Numerous studies have become available to help agencies determine if
sand fits into their winter maintenance arsenal or if customer satisfaction can be
provided with the use of some other technique or ice melting material. Let’s look at that research in the areas of
public health and safety, economics and environmental protection.
Winter roadway maintenance plays a major role in public safety. The foremost reason for treating winter roads has
been to prevent skidding accidents and their resultant injuries, deaths and property
damage losses by maintaining a safe roadway surface.
Another health concern is introduced when sand is used for roadway
maintenance: adding to the already high ambient airborne particulate levels, which impair
air quality. The shorthand term is “PM10.” PM10 is the very small airborne
particulate matter (PM) that is inhaled into the lungs and can cause respiratory health
problems, including lung cancer. A key study,
in 1995, documented “The Contribution of Road Sanding and Salting Material on Ambient
PM10 Concentrations.” The
research in Albany, NY; Denver, CO; and Reno, NV studied the impacts of wintertime road
sanding and/or salting on ambient particulate loadings.
The researchers did not examine the relevant question of whether salt
particulates should be of concern at all since salt particles are soluble and do not lodge
in the lung as does sand particulate. The
results were striking – and disturbing for users of sand in winter maintenance:
Any agency in an air quality non-attainment area, will find these
results compelling. Either transportation
agencies will decide to limit or eliminate their use of sanding or they face the likely
imposition of specific limitations by environmental agencies to help achieve better air
quality. Denver is a good example. Shortly after the study was completed, the U.S.
EPA approved the State of Colorado’s air quality improvement plan including a new
section dedicated to “Improved Street Sweeping” which requires “that any
entity responsible for applying street sanding material within the Denver Central Business
District shall clean all streets using vacuum sweepers or a more effective technology
within four days of each sanding episode…”
Perhaps Denver’s notorious “Brown Cloud” will become an
historical footnote. After completing its own
study, Utah found it faced the same problem and amended their state clean air plan to
virtually replace sand with salt.
Safety is the other
“public health” concern. Snowfighting’s
primary objective is reducing traffic crashes, injuries and deaths. Maintaining roadway friction is the operating
criterion. And sand covered up by snow or
swept off the road by traffic doesn’t provide roadway friction. Many studies have confirmed salt’s
effectiveness in maintaining friction and reducing traffic crashes. One in every five crashes during winter months
will be avoided using plowing and salting techniques – and, during storms, that ratio
improves from 20% reduction to prevention of nearly nine of ten accidents that would
otherwise occur.
Transportation agencies do a great job maintaining the Interstates
and arterial roads; lesser-traveled residential streets and rural two-lane roads are more
challenging. And, our nation’s most
dangerous roads – with an accident rate about three times that of our Interstate
highways – are rural two-lane roads.
This past winter, the Iowa Department of Transportation and the Iowa
Highway Research Board completed its important study, “The Use of Abrasives in Winter
Maintenance.” The study examines the use of sand to increase friction between
vehicles and the snow- or ice-covered pavement. As
in many other states, many, mostly smaller, agencies in Iowa use sand as a standard part
of their winter maintenance program. Based on
a review of both the existing literature and the current practice, the study develops a
series of recommended practices for sand usage. Principal
conclusion: “… applying abrasives
dry is of limited value in providing lasting friction enhancement. This represents a substantial change in current
practice. Nonetheless, the results of a
variety of studies are unequivocal in finding that abrasives applied to roads where
significant traffic travels at high speeds are swept off the road rapidly, remaining in
place (and providing friction enhancement) for somewhere between 10 and 100 vehicle
passages, at most.” A
“solution” that dissipates after one or a few dozen cars pass is hardly a
solution at all, the report infers.
Doing no winter maintenance is bad
economics: the cost of responding to an
entire winter’s snow- and ice-events is less than the economic losses of wages,
retail sales and tax revenues for a single day of inadequate roadway maintenance. Still, like other public services, winter
maintenance should aim to get the most “bang for a buck.”
Accident reduction on two-lane highways was less using sand than
straight salt according to a 1996 study by David A. Kuemmel and Quasi Bari of Marquette
University. Not only was salt superior to
sand to achieve safe driving conditions, it was more affordable. In fact, the study found that salt applications
paid for themselves after just 25 minutes on two-lane highways (35 minutes on freeways)
whereas agencies using sand never recovered their costs associated with purchasing,
storing and applying the sand. And the
study did not even include the significant costs of cleaning up the sand from the roadside
or catch basins. The Marquette study
confirmed earlier work in Germany, which found that sand actually cost more because higher
application rates are used and more applications are made.
Former Washington DOT snowfighter Dale Keep estimated in the late 1980s the
cost of using sand for winter maintenance (add to the purchase price shipping costs,
handling, storage, application, clean-up costs, and any other cost associated with its
use): “the true cost of sand,
including sweeping was $152 per yard…In today’s figures its probably closer to
$180 per yard.” Salt is much more
cost-effective.
Along with air quality and its human health concerns, highway runoff is also a serious environmental problem. The environmental impacts of chloride salt runoff have been well studied. Most highway agencies also know that using any type of sand entails a clean up cost. Not discounting the harm such sand can cause to the stormwater runoff infrastructure; there is a potential threat to receiving waters. In June 2001, the U.S. General Accounting Office (GAO) issued its report entitled Water Quality - Better Data and Evaluation of Urban Runoff Programs Needed to Assess Effectiveness. GAO recommends that EPA work with states to develop program goals, establish standards for reporting on program costs and effectiveness, and review reported water quality data to assess if the current program is improving the quality of the nation's waters and how much they cost.
Because “global warming” hasn’t prevented people from living in very cold climates, we will always need to provide lifesaving winter maintenance. Salt isn’t the answer when temperatures are way below freezing; sand has its place. We need to know more. Because it is a small and shrinking use of sand, winter maintenance using sand deserves more study to add effectiveness to sand usage. Three alternative approaches to find a way of getting sand to stick to the snow or ice-covered pavement are: prewetting the sand or abrasive at the spinner; heating the sand or abrasive to high temperatures (about 180° C seems to be effective) just prior to being placed on the road; and mixing the sand or abrasive with hot water (about 90° C) as they are placed on the road. While all three of these methods show some promise, none is fully developed as part of the standard winter maintenance strategy for any agency in the U.S. or around the world.
Therefore in the absence of an efficient technique to maximize the use of sand or abrasives, with the existing evidence and research, and the environmental burden both to air and water resources, very limited use during extreme winter conditions or no use of sand or abrasives should be your standing policy. Highway agencies that choose to utilize sand or abrasives will continue to come under stronger scrutiny while striving to meet their customers’ expectations for safety and mobility.
For further information, see the article "Pros and Cons of Sand on Ice and Snowpack" University of New Hampshire Technology Transfer Center (Fall 2001). And for a discussion of the cost-benefit of salt versus salt-sand mixtures, this study from Marquette University.