Road Salt Use in the United States

[Pages:14]2 Road Salt Use in the United States

Under many snow and ice conditions, the use of deicing chemicals is necessary to maintain clear pavements. In terms of both time and budget, common salt, or sodium chloride, is widely regarded as the most effective means of deicing highways. Salt is by far the most commonly used deicing chemical in the United States; it is spread at a rate of approximately 10 million tons per year. This chapter provides general background information on the use of road salt, including trends in usage, application and storage practices, use by region and jurisdictional level, and annual spending on salting operations. The chapter concludes with a brief discussion of some of the benefits of deicing and efforts being made by highway agencies to manage their salting programs.

TRENDS IN ROAD SALT USE

The use of road salt has paralleled changes in the size and importance of the nation's highway system. Before the 1940s, highway departments relied mostly on plowing and abrasives (e.g., sand and cinders) to keep roadways open after winter storms. Salt was used primarily as an additive to prevent freezing of sandpiles. During the winter of 1941?1942, New Hampshire became the first state to adopt a general policy of using salt, although a total of only 5,000 tons of salt was spread on the nation's highways that winter (TRB 1974, 2).

17

1

HIGHWA8Y DEICING

After World War II, as the expanding highway system became essential to the public and the national economy, road salt use began to soar. The bare-pavement concept, under which motorists could expect snow- and ice-free pavements shortly after storms, soon became a policy in most cities and their suburbs. As a result, salt use doubled every 5 years during the 1950s and 1960s growing from 1 million tons in 1955 to nearly 10 million tons less than 15 years later (Figure 2-1).

Road salt use has leveled off during the past 20 years. Whereas salt use increased rapidly during the 1950s and 1960s because it was replacing abrasives, by the 1970s this conversion was nearly complete. Also, at about this time, many of salt's adverse effects were becoming well known, causing many highway agencies to reevaluate their salting practices. Through practical experience and with guidance from government and industry, many highway agencies started managing their salting programs, for example, by calibrating spreading equipment and establishing formal salt use policies. Partly because of these changes, annual salt use has fluctuated from 8 million to 12 million tons during the past 20 years, with year-to-year fluctuations depending mainly on winter conditions.

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22 HIGHWAY DEICING

TABLE 2-1 OFFICIAL SALT USE POLICIES IN VARIOUS STATES

Region and State Summary of General Policy

New England Connecticut Massachusetts New Hampshire

Middle Atlantic Maryland West Virginia

Great Lakes Michigan

Ohio

Wisconsin

Plains Iowa

Kansas

West Colorado - California

Salt applied at 215 lb/lane-mi on multilane roads; no more than 150 lb/lane-mi on two-lane state highways

Salt applied at less than 300 lb/lane-mi on state highways

Salt application guideline of 250 to 300 lb/lane-mi on state highways

Salt application guideline of 300 to 500 lb/lane-mi on state highways

Salt application guideline of 100 to 250 lb/lane-mi, usually mixed with abrasives, except in cities

Salt applied at 225 lb/lane-mi on primary highways. Salt and sand mixtures used on lower-priority roads, depending on storm temperature and severity

Salt applied at 200 to 300 lb/lane-mi on Interstate and primary highways; 100 to 200 lb/lane-mi, with abrasives on secondary roads; no more than 100 to 200 lb/lane-mi on low-priority roads

Salt application rates of 100 to 300 lb/lane-mi recommended; additional salt use restrictions related to pavement temperature in place

Salt applied at 150 lb/lane-mi (mixed with sand) on Interstates and other arterials; 100 lb/lane-mi on collectors; no salt used on local roads

Salt applied at 100 to 250 lb/lane-mi (mixed with sand) on Interstates, freeways, and other roads with 2,500+ ADT; less on roads with 750 to 2,500 ADT; no salt used on roads with < 750 ADT

Salt only with abrasives; rates not defined Salt applied at 500 lb/lane-mi on some mountain

highways

NOTE:Althoughpoliciesoftenidentifyanidealsaltapplicationrateforequipmentcali-

bration, they seldom regulate the timing and frequency of applications. Application timing and frequency are typically determined by the maintenance engineer in charge during the storm. Data in the table are from states that responded to relevant questions in survey. ADT = average daily traffic. SOURCE:TRB survey of state highway agencies.

SALT USE BY JURISDICTION AND REGION

Nationwide, there are more than 3.8 million mi of public highway and streets. Except for minor amounts of mileage on federal lands, practically all of these roads are maintained by state and local high-

Road Salt Use in the United States 23

TABLE 2-2 AVERAGE ANNUAL SALT LOADINGS ON STATE HIGHWAYS WHERE SALT IS NORMALLY APPLIED

Region and State

New England Maine Massachusetts New Hampshire Vermont

Middle Atlantic Delaware Maryland New Jersey New York Virginia West Virginia

Great Lakes Illinois Indiana Michigan Ohio Wisconsin

Plains Iowa Minnesota Missouri Nebraska Oklahoma South Dakota

Mountain and West Alaska California Idaho Nevada New Mexico

Average Annual Loading (tons/lane-mile)

8.0

19.4 16.4 17.1

9.0 7.1 6.7 16.6 3.0 6.3

6.6 9.0 12.9 9.1 9.2

3.8 5.0 1.0 1.5 1.5 1.0

1.2 3.0 0.3 1.9 0.5

NOTE: Data are from only those states that responded

, questions in survey.

SOURCE: TRB survey of state highway agencies.

to relevant

way agencies. As the data in Table 2-3 indicate, state highway agencies (including toll authorities) administer about 20 percent of this mileage, including all Interstates and virtually all other primary highways. Local governments (counties, cities, and towns) have jurisdiction over about three-quarters of all mileage, although a large share consists of low-volume secondary roads and residential streets.

Figure 2-4 shows the share of total salt usage by state, toll, county, and municipal highway agencies, derived from Salt Institute data and

24 HIGHWAY DEICING

FIGURE 2-3 Highway maintenance yard. Top: Salt hopper and spreader truck. Bottom: Salt storage shed.

the survey of state highway agencies conducted for this study. Because of the heavy traffic demands on primary highways, states and toll authorities are especially heavy users of salt, accounting for about one-half of all the salt used nationally. The next largest users are municipal agencies--especially large cities--which account for about 35 percent of salt use. County highway agencies account for the remaining 15 percent. Because counties are often responsible for

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