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9 CHAPTER 4 PERFORMANCE-BASED LEVEL OF SERVICE The definition of terms, concepts, and a suggested Pavement able amount of loose snow/ice is established, the necessary Snow and Ice Condition (PSIC) rating system were described equipment resource can be determined. First, the local plow- in Chapter 2 in the section entitled Performance Measuring of ing production rate in terms of lane miles per hour (including Level of Service (LOS). When defining LOS goals, two time reloading and deadheading) has to be determined. This, in frames relative to a winter weather event need to be considered: conjunction with design snowfall rate, yields the cycle time required to meet the "accumulation" goal. Sufficient equip- Within-winter weather event and ment has to be provided to achieve the desired cycle time(s). After-end-of-winter weather event. The second issue is the condition of the snow/ice pave- ment interface in terms of bond or packed snow/ice. This is Higher LOS are associated with "better" within-event pave- largely a function of pavement temperature, the type of mate- ment ice conditions and more rapid achievement of "better" rials treatment being provided, materials application rate, and or "bare" pavement conditions after the event ends. cycle time. Generally, cycle times shorter than 1.5 hours using straight chemicals and plowing will allow a high within-event level of service. THE "DESIGN" WINTER WEATHER EVENT A winter weather event having a snowfall rate of "X" inches AFTER-END-OF-WINTER WEATHER EVENT per hour should be chosen as a basis for determining what level LEVEL OF SERVICE of service can be provided with existing resources or deter- mining the necessary resources to provide a desired level of The after-end-of-event LOS is usually expressed as a time service. "X" should be a rate that is only exceeded in "Y" per- to achieve particular pavement surface conditions in terms of cent of snowfall records in an average year (from climatolog- ice or snow coverage, or PSIC level. ical records). "Y" of about 20 percent can be selected (7). ESTABLISHING LEVEL OF SERVICE GOALS WITHIN-WINTER WEATHER EVENT LEVEL OF SERVICE The first step in the process of establishing LOS goals is to prioritize the roadway system and particular locations within A within-winter weather event has two intertwined compo- the system into some type of LOS system. This is typically a nents--the amount of loose snow/ice/slush that is allowed to numeric, alphabetic, or color system. The next step is to assign accumulate between plowing cycles and the condition of the both within-winter weather event and after-end-of-winter ice/pavement interface in terms of bond and packed snow/ice. weather event LOS goals. These goals may be described in The amount of loose snow allowed to accumulate on the terms of a PSIC as shown in Table 6 or a variety of other roadway between plowing cycles is usually the driving force descriptors. The final step is a reality check to ensure that suf- for plowing resource requirements. Plowing operations are ficient capability to meet the goals for the "design" condi- limited to one lane at a time while material spreading opera- tions is available. Table 6 is an example of LOS goals for a tions can treat more than one lane at a time. Once the allow- small roadway system.

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10 TABLE 6 Example of level of service assignment Highway segment Within-event LOS After-end-of-event LOS LOS Maximum snow Hours after a Route Mile post class PSIC accumulation (in.) PSIC end-of-event 15 2-25 2 3 1.5 1 2.0 8 175-186 4 5 2.0 2 6.0 16 37-51 3 4 1.5 2 3.0 5 256-271 3 4 1.5 2 3.0 2 0-4 2 3 1.5 1 2.0 10 277-291 4 5 2.0 2 6.0 10 291-315 3 4 1.5 2 3.0 4 26-32 1 2 1.0 1 1.5 4 32-50 3 4 1.5 2 3.0 Main Street 1 2 1.0 1 1.5 Baxer Bridge 1 1 0.0 1 0.0 a "1" is the highest; 4 is the lowest LOS class.