Click for next page ( 5

The National Academies of Sciences, Engineering, and Medicine
500 Fifth St. N.W. | Washington, D.C. 20001

Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement

Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 4
4 Centerline bare, SNOW AND ICE CONTROL OPERATIONAL Wheel path bare, CONSIDERATIONS RELATING TO LEVEL OF SERVICE Loose snow covered (percent area and depth), Packed snow covered (percent area and depth), The primary snow and ice control operational considerations Bare (percent area), relating to LOS are cycle time, available material treatments, Thin ice covered (percent area), weather conditions, site conditions, and traffic considerations. Thick ice covered (percent area), Cycle time is primarily a function of the number of per- Dry, sonnel and the amount of equipment available to treat the Damp, assigned roadway system or route. Other factors, including traf- Slush (percent area and depth), fic volume/speed, traffic control devices, roadway geometry/ Frost, and complexity, and the location of material stockpiles also con- Wet. tribute to achievable cycle time. LOS and cycle time of maintenance treatment operations Using the descriptors above together with traffic flow and are clearly interconnected. The LOS and cycle time for a other visual information, a Pavement Snow and Ice Condi- facility will largely be determined by the importance or func- tion (PSIC) can be established for any point in time. The tional classification of the road, which may be strongly related descriptions of the various PSICs appear in Table 1. to the roadway's average daily traffic volume (ADT) (5). Whatever performance measure is chosen, it must be part of High winter maintenance LOS requirements are described a continuing evaluation plan that addresses individual winter many times as "bare pavement" policies. Anti-icing strategies weather events; early, mid, and late winter season events that with appropriate tactics have been shown to be consistent tend to have similar characteristics; and full winter seasons. with the requirements of a high-LOS facility (3). This will allow critical judgment to be made on resource lev- The type of material treatments an agency is capable of els, strategies and tactics, materials choices and materials delivering has a major impact on achievable LOS. Agencies application rates. capable of providing appropriate liquid and/or solid chemi- TABLE 1 Descriptions of pavement snow and ice conditions (PSIC) Condition 1: All snow and ice are prevented from bonding and accumulating on the road surface. Bare/wet pavement surface is maintained at all times. Traffic does not experience weather-related delays other than those associated with wet pavement surfaces, reduced visibility, incidents, and "normal" congestion. Condition 2: Bare/wet pavement surface is the general condition. There are occasional areas having snow or ice accumulations resulting from drifting, sheltering, cold spots, frozen melt-water, etc. Prudent speed reduction and general minor delays are associated with traversing those areas. Condition 3: Accumulations of loose snow or slush ranging up to (2 in.) are found on the pavement surface. Packed and bonded snow and ice are not present. There are some moderate delays due to a general speed reduction. However, the roads are passable at all times. Condition 4: The pavement surface has continuous stretches of packed snow with or without loose snow on top of the packed snow or ice. Wheel tracks may range from bare/wet to having up to (1.5 in.) of slush or unpacked snow. On multilane highways, only one lane will exhibit these pavement surface conditions. The use of snow tires is recommended to the public. There is a reduction in traveling speed and moderate delays due to reduced capacity. However, the roads are passable. Condition 5: The pavement surface is completely covered with packed snow and ice that has been treated with abrasives or abrasive/chemical mixtures. There may be loose snow of up to (2 in.) on top of the packed surface. The use of snow tires is required. Chains and/or four-wheel drive may also be required. Traveling speed is significantly reduced and there are general moderate delays with some incidental severe delays. Condition 6: The pavement surface is covered with a significant buildup of packed snow and ice that has not been treated with abrasives or abrasives/chemical mixtures. There may be (2 in.) of loose or wind-transported snow on top of the packed surface due to high snowfall rate and/or wind. There may be deep ruts in the packed snow and ice that may have been treated with chemicals, abrasives, or abrasives/chemical mixtures. The use of snow tires is the minimum requirement. Chains and snow tire equipped four-wheel drive are required in these circumstances. Travelers experience severe delays and low travel speeds due to reduced visibility, unplowed loose, or wind-compacted snow, or ruts in the packed snow and ice. Condition 7: The road is temporarily closed. This may be the result of severe weather (low visibility, etc.) or road conditions (drifting, excessive unplowed snow, avalanche potential or actuality, glare ice, accidents, vehicles stuck on the road, etc.).

OCR for page 4
5 cal treatment will achieve higher LOS than those who pro- ational difficulty include curvature, variable pavement widths, vide only mixtures of chemicals and abrasives or no material and many of those variables listed in next chapter. These lat- treatment at all. ter items directly or indirectly can contribute to the presence The character and intensity of particular winter weather of ice/pavement bond because of special needs imposed on events influence how long chemical snow and ice control snow and ice control field operations. treatments will remain effective and the amount of snow/ice Traffic considerations include those relating to operational accumulation on the roadway between plowing cycles. The difficulty (e.g., slow- and fast-moving traffic, stranded block- climatology of a particular area defines the historical average ing vehicles); timing (e.g., rush-hour, congestion); and influ- (usually over a 30-year period) of the type and amount of ences on treatment effectiveness and longevity. The variation frozen precipitation the area can be expected to receive in an of traffic rate throughout a 24-hr period is an important con- average winter. What is important for winter maintenance sideration in the operational decision-making process. operations in a given area is not so much climatology, but Vehicular traffic can affect the pavement surface in sev- the distribution of precipitation types associated with winter eral ways. Tires compact snow, abrade it, displace, or dis- weather events. Winter maintenance forces across the United perse it. Heat from tire friction, engine, and the exhaust sys- States need to be prepared to treat a wide variety of precipi- tem can add measurable heat to the pavement surface. Traffic tation types, even within a given winter weather event. Only wheel passages can help in the deicing of local streets when the distribution of the likelihood of precipitation type occur- treated in the early morning hours. Traffic can also result in rence changes from area to area, or agency to agency. applied chemicals and abrasives being blown from the pave- The three site conditions of major importance are (1) pave- ment surface when applied before precipitation. Thus, traffic ment temperature, (2) the amount of snow/ice remaining on can have both positive and negative influences on the effec- the roadway after plowing and/or before chemical treatment, tiveness of snow and ice control operations. However, most and (3) most significantly, the presence or absence of ice/ of the influences are difficult to quantify. Further research is pavement bond. Other site conditions that relate more to oper- needed to quantify the effects of traffic.