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42 Utilization is an indicator of curbside roadway level of Through traffic delay is the amount of time required service, which provides an overall indication of the quality of for a vehicle to traverse the entire curb length. To deter- the experiences of drivers and passengers using the curbside mine through traffic delay, the unimpeded travel time for roadway. LOS C is a desirable planning target for a medium- through traffic on the curbside roadway is subtracted or small-hub airport, both for the design of new curbside from the actual travel time to obtain the amount of through roadways and for analyzing an existing facility. LOS D is accept- traffic delay per vehicle. When designing a new curbside able for an existing curbside roadway at a large-hub airport, roadway, the delay to through traffic should ideally be near recognizing that on some peak days of the year, the level of zero. For existing roadways, delays of up to 15 seconds service may decrease to LOS E or less. Level of service is esti- per vehicle may be acceptable, recognizing that the delays mated separately for through traffic and for curbside loading/ could be significantly higher on peak days of the year. The unloading traffic. acceptable amount of delay for through vehicles must be When additional performance measures, as described set by the airport operator based on the design of the land- below, are required to supplement curbside utilization, the side circulation system and the number of other delays analysis is conducted using a microsimulation model. Such experienced by through vehicles on other portions of the supplemental measures cannot be accurately determined roadway circulation system. For example, if through vehi- without the use of a microsimulation model, either quanti- cles must pass several curbside loading/unloading areas, tatively or in the field (i.e., they are difficult to quantify then delays at each curbside area will be less tolerable. using field surveys). For example, the use of a microsimula- Curbside loading/unloading delay is the amount of time tion model would help document the ability of an existing a vehicle requires to pull into a curbside stall, load or un- curbside roadway to accommodate future demand, or to load passengers, and exit. The minimum time necessary to quantify the benefits resulting from alternative curbside drop off or pick up a passenger during uncongested peri- improvement options. These supplemental performance ods (i.e., the average dwell time) should be subtracted from measures include the total average observed time to obtain the amount of curbside loading/unloading delay. Curbside delays of up to Number of vehicles parked in the second and third lanes. 30 seconds are acceptable when designing a new roadway. The number of through lanes blocked by parked or park- Delays of up to 60 seconds per vehicle are acceptable for ing vehicles (and the proportion of the modeled hour dur- existing roadways. ing which this blockage occurs) is an indicator of the extent of roadway congestion. It is also an indirect indication of As shown by the checkmarks in Table 5-1, use of these per- the ability of motorists to enter/exit and stop at their pre- formance measures requires different analysis methods. ferred curbside locations since it is difficult for motorists When curbside roadways are being analyzed using microsim- stopped in the curb lane to exit when triple parking occurs ulation models, it is possible to consider the number of vehi- without the intervention of traffic control officers. Queue length. Queue length is the number of vehicles wait- cles parked in the second and third lanes, the length and ing to enter the curbside roadway or a specific curbside duration of curbside queues, and average vehicle speeds (or parking area expressed in terms of the distance that the delays). Without the aid of microsimulation models, it is dif- vehicle queue extends back from the curbside parking area ficult to accurately estimate vehicle parking patterns, travel or point of congestion. Queue lengths are estimated for times and delays, and queue lengths because of the relatively different levels of probable occurrence. The mean queue short distances on curbside roadways being analyzed and the length has a 50% probability of being exceeded some time difficulty estimating queue lengths through other means. during the hour. The 95% queue length has a 5% probabil- When curbside roadways are being analyzed using the quick- ity of being exceeded. The 95% queue length is typically estimation or macroscopic methods described in this chapter, used for design purposes. the appropriate performance measures are curbside utiliza- Queuing duration. The queuing duration (in minutes) tion and the corresponding levels of service. indicates how long the congestion will last, and is useful for comparing two potential design solutions, neither of which Level-of-Service Definitions completely eliminates queuing. Ideally, the queuing dura- for Airport Curbside Roadways tion is zero for a new curbside roadway, and less than one hour for an existing curbside roadway. The primary element defining the level of service of an air- Average vehicle delay. Average vehicle delay consists of port curbside roadway is the ability of motorists to enter and two components--through traffic delay and curbside exit the curbside space of their choice (e.g., one near their air- loading/unloading delay. line door or other chosen destination). As roadway demand