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3CHAPTER 2 LEVEL OF SERVICE Level of service (LOS) in the context of roadway snow and ice control operations is a set of operational guidelines and pro- cedures that establish the timing, type, and frequency of treat- ments. The maintenance actions are directed toward achieving specific pavement condition goals for various highway sec- tions. Examples of LOS for highways, roads, and streets under snow and ice control conditions are given in AASHTOâs âGuide for Snow and Ice Controlâ (5). How highway agen- cies characterize LOS, how they assign LOS goals, and how they measure the performance of maintenance operations in achieving the LOS goals are very important topics. These are briefly described below. HOW AGENCIES CHARACTERIZE LEVEL OF SERVICE There are several ways (singularly and in combination) by which highway agencies characterize the LOS they pro- vide. These include level of effort, priority of treatment, types of treatments, and results in terms of pavement con- ditions at various points in time during and after snow and ice events. The level of effort category includes assigning more peo- ple and equipment to higher priority routes, providing more or less effort during certain time frames, varying the number of people and equipment providing treatment in relationship to the predicted severity of the event, and so on. The priority of treatment category includes giving first and/or more frequent treatment to higher traffic routes, high accident/problem locations, commercial/business locations, school bus routes, transit routes, health facilities, fire house locations, and schools. Some highway agencies use a system of providing treatment on a highway priority basis whereby the next lower category of highway is not treated until higher category roads are in âsatisfactoryâ condition. In the type of treatment category, the treatments at various locations are specifically defined. Examples include sanding hills and intersections, plowing-only on certain roads, using nonchloride or reduced chloride applications in certain areas, anti-icing areas, pre-treating areas, applying chemicals only at the beginning and end of the event, and so on. RECOMMENDED LEVEL OF SERVICE GOALS A good way to define LOS is in terms of results at various points in time. Examples include maximum accumulation of snow on highways during a storm, absence of pack or bond during a storm, bare/wet pavement (x) hours after end-of- event, plowed and sanded (x) hours after end-of-event, fric- tion number > (y) (x) hours after end-of-event, road plowed, and road passable. ASSIGNING LEVEL OF SERVICE GOALS There are two fundamental approaches for highway agen- cies to use when assigning their LOS goals. The first is to evaluate existing resources and direct them toward providing a balanced LOS on a priority of treatment basis. This is real- istically the more common approach. The second, and pre- ferred, approach is to assign pavement condition goals at intervals within and after a âdesign stormâ of âXâ inches of snow per hour to the various priority elements of the high- way system. Using this, and production rate (lane-miles per hour) of equipment (including deadheading and reloading) in both the plowing and materials spreading modes, the neces- sary personnel and equipment can then be determined to pro- vide the desired LOS. PERFORMANCE MEASURING OF LEVEL OF SERVICE A variety of performance measures are being tried and used relative to LOS. These include (in order of popularity) pavement conditions (visual) at various points in time (some agencies use pictorial reference templates as an aid to condi- tion observers); performance indices that relate the amount of time pavement areas are snow/ice covered to total storm time (visual); report cards (customer satisfaction surveys); and friction measurements at various points in time and rat- ing slipperiness at various points in time based on vehicle handling characteristics. The visual approach appears to be gaining in popularity in the United States and abroad. Examples of visual character- ization of roadway surfaces include the following:
⢠Centerline bare, ⢠Wheel path bare, ⢠Loose snow covered (percent area and depth), ⢠Packed snow covered (percent area and depth), ⢠Bare (percent area), ⢠Thin ice covered (percent area), ⢠Thick ice covered (percent area), ⢠Dry, ⢠Damp, ⢠Slush (percent area and depth), ⢠Frost, and ⢠Wet. Using the descriptors above together with traffic flow and other visual information, a Pavement Snow and Ice Condi- tion (PSIC) can be established for any point in time. The descriptions of the various PSICs appear in Table 1. Whatever performance measure is chosen, it must be part of a continuing evaluation plan that addresses individual winter weather events; early, mid, and late winter season events that tend to have similar characteristics; and full winter seasons. This will allow critical judgment to be made on resource lev- els, strategies and tactics, materials choices and materials application rates. 4 SNOW AND ICE CONTROL OPERATIONAL CONSIDERATIONS RELATING TO LEVEL OF SERVICE The primary snow and ice control operational considerations relating to LOS are cycle time, available material treatments, weather conditions, site conditions, and traffic considerations. Cycle time is primarily a function of the number of per- sonnel and the amount of equipment available to treat the assigned roadway system or route. Other factors, including traf- fic volume/speed, traffic control devices, roadway geometry/ complexity, and the location of material stockpiles also con- tribute to achievable cycle time. LOS and cycle time of maintenance treatment operations are clearly interconnected. The LOS and cycle time for a facility will largely be determined by the importance or func- tional classification of the road, which may be strongly related to the roadwayâs average daily traffic volume (ADT) (5). High winter maintenance LOS requirements are described many times as âbare pavementâ policies. Anti-icing strategies with appropriate tactics have been shown to be consistent with the requirements of a high-LOS facility (3). The type of material treatments an agency is capable of delivering has a major impact on achievable LOS. Agencies capable of providing appropriate liquid and/or solid chemi- 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.). TABLE 1 Descriptions of pavement snow and ice conditions (PSIC)
cal treatment will achieve higher LOS than those who pro- vide only mixtures of chemicals and abrasives or no material treatment at all. The character and intensity of particular winter weather events influence how long chemical snow and ice control treatments will remain effective and the amount of snow/ice accumulation on the roadway between plowing cycles. The climatology of a particular area defines the historical average (usually over a 30-year period) of the type and amount of frozen precipitation the area can be expected to receive in an average winter. What is important for winter maintenance operations in a given area is not so much climatology, but the distribution of precipitation types associated with winter weather events. Winter maintenance forces across the United States need to be prepared to treat a wide variety of precipi- tation types, even within a given winter weather event. Only the distribution of the likelihood of precipitation type occur- rence changes from area to area, or agency to agency. The three site conditions of major importance are (1) pave- ment temperature, (2) the amount of snow/ice remaining on the roadway after plowing and/or before chemical treatment, and (3) most significantly, the presence or absence of ice/ pavement bond. Other site conditions that relate more to oper- 5 ational difficulty include curvature, variable pavement widths, and many of those variables listed in next chapter. These lat- ter items directly or indirectly can contribute to the presence of ice/pavement bond because of special needs imposed on snow and ice control field operations. Traffic considerations include those relating to operational difficulty (e.g., slow- and fast-moving traffic, stranded block- ing vehicles); timing (e.g., rush-hour, congestion); and influ- ences on treatment effectiveness and longevity. The variation of traffic rate throughout a 24-hr period is an important con- sideration in the operational decision-making process. Vehicular traffic can affect the pavement surface in sev- eral ways. Tires compact snow, abrade it, displace, or dis- perse it. Heat from tire friction, engine, and the exhaust sys- tem can add measurable heat to the pavement surface. Traffic wheel passages can help in the deicing of local streets when treated in the early morning hours. Traffic can also result in applied chemicals and abrasives being blown from the pave- ment surface when applied before precipitation. Thus, traffic can have both positive and negative influences on the effec- tiveness of snow and ice control operations. However, most of the influences are difficult to quantify. Further research is needed to quantify the effects of traffic.
