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Airport Curbside and Terminal Area Roadway Operations (2010)

Chapter: Chapter 5 - Evaluating Airport Curbside Operations

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Suggested Citation:"Chapter 5 - Evaluating Airport Curbside Operations." National Academies of Sciences, Engineering, and Medicine. 2010. Airport Curbside and Terminal Area Roadway Operations. Washington, DC: The National Academies Press. doi: 10.17226/14451.
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Suggested Citation:"Chapter 5 - Evaluating Airport Curbside Operations." National Academies of Sciences, Engineering, and Medicine. 2010. Airport Curbside and Terminal Area Roadway Operations. Washington, DC: The National Academies Press. doi: 10.17226/14451.
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Suggested Citation:"Chapter 5 - Evaluating Airport Curbside Operations." National Academies of Sciences, Engineering, and Medicine. 2010. Airport Curbside and Terminal Area Roadway Operations. Washington, DC: The National Academies Press. doi: 10.17226/14451.
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Suggested Citation:"Chapter 5 - Evaluating Airport Curbside Operations." National Academies of Sciences, Engineering, and Medicine. 2010. Airport Curbside and Terminal Area Roadway Operations. Washington, DC: The National Academies Press. doi: 10.17226/14451.
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Suggested Citation:"Chapter 5 - Evaluating Airport Curbside Operations." National Academies of Sciences, Engineering, and Medicine. 2010. Airport Curbside and Terminal Area Roadway Operations. Washington, DC: The National Academies Press. doi: 10.17226/14451.
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Suggested Citation:"Chapter 5 - Evaluating Airport Curbside Operations." National Academies of Sciences, Engineering, and Medicine. 2010. Airport Curbside and Terminal Area Roadway Operations. Washington, DC: The National Academies Press. doi: 10.17226/14451.
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Suggested Citation:"Chapter 5 - Evaluating Airport Curbside Operations." National Academies of Sciences, Engineering, and Medicine. 2010. Airport Curbside and Terminal Area Roadway Operations. Washington, DC: The National Academies Press. doi: 10.17226/14451.
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Suggested Citation:"Chapter 5 - Evaluating Airport Curbside Operations." National Academies of Sciences, Engineering, and Medicine. 2010. Airport Curbside and Terminal Area Roadway Operations. Washington, DC: The National Academies Press. doi: 10.17226/14451.
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Suggested Citation:"Chapter 5 - Evaluating Airport Curbside Operations." National Academies of Sciences, Engineering, and Medicine. 2010. Airport Curbside and Terminal Area Roadway Operations. Washington, DC: The National Academies Press. doi: 10.17226/14451.
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Suggested Citation:"Chapter 5 - Evaluating Airport Curbside Operations." National Academies of Sciences, Engineering, and Medicine. 2010. Airport Curbside and Terminal Area Roadway Operations. Washington, DC: The National Academies Press. doi: 10.17226/14451.
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Suggested Citation:"Chapter 5 - Evaluating Airport Curbside Operations." National Academies of Sciences, Engineering, and Medicine. 2010. Airport Curbside and Terminal Area Roadway Operations. Washington, DC: The National Academies Press. doi: 10.17226/14451.
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Suggested Citation:"Chapter 5 - Evaluating Airport Curbside Operations." National Academies of Sciences, Engineering, and Medicine. 2010. Airport Curbside and Terminal Area Roadway Operations. Washington, DC: The National Academies Press. doi: 10.17226/14451.
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Suggested Citation:"Chapter 5 - Evaluating Airport Curbside Operations." National Academies of Sciences, Engineering, and Medicine. 2010. Airport Curbside and Terminal Area Roadway Operations. Washington, DC: The National Academies Press. doi: 10.17226/14451.
×
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Page 54
Suggested Citation:"Chapter 5 - Evaluating Airport Curbside Operations." National Academies of Sciences, Engineering, and Medicine. 2010. Airport Curbside and Terminal Area Roadway Operations. Washington, DC: The National Academies Press. doi: 10.17226/14451.
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Suggested Citation:"Chapter 5 - Evaluating Airport Curbside Operations." National Academies of Sciences, Engineering, and Medicine. 2010. Airport Curbside and Terminal Area Roadway Operations. Washington, DC: The National Academies Press. doi: 10.17226/14451.
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Suggested Citation:"Chapter 5 - Evaluating Airport Curbside Operations." National Academies of Sciences, Engineering, and Medicine. 2010. Airport Curbside and Terminal Area Roadway Operations. Washington, DC: The National Academies Press. doi: 10.17226/14451.
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41 This chapter presents measures of curbside roadway per- formance, definitions of curbside roadway levels of service, and a hierarchy of analytical methods for estimating curb- side roadway capacities and levels of service. It also describes use of a macroscopic method, QATAR, for analysis of air- port curbside roadways, and explains the use of this method. Appendix G documents the queuing theory and assumptions used in QATAR. In evaluating airport curbside roadway operations, analy- ses of both the curbside lanes (where motorists stop to pick up or drop off passengers) and the adjacent through lanes are required. As described in Chapter 2, these analyses are neces- sary because double- or triple-parked vehicles impede or delay the flow of vehicles in the adjacent through lanes.* As a result, the capacity of the through lanes decreases as demand for curb- side space approaches or exceeds the capacity of a curbside roadway segment, causing double or triple parking. As described in more detail later in this chapter, the capac- ity of curbside pickup and drop-off areas depends on the num- ber of lanes airport management allows to be used for vehicles to stop, load, or unload. For example, at airports where double parking is prohibited, curbside capacity equals the effective length of the lane next to the curb. At airports where double parking is allowed, curbside capacity equals twice the length of this lane. In this chapter, methods of estimating the volumes, capac- ities, and levels of service of the curbside lanes and the through lanes are presented separately. However, when estimating air- port curbside roadway capacities and levels of service, it is necessary to consider the operations of both the curbside lane and the through lanes concurrently because the capacity and level of service of an airport curbside roadway system is deter- mined by the component that has the lowest capacity or pro- vides the poorest level of service. The methods and data presented in this chapter represent the best available information concerning airport roadway operations and the consensus of the research team, the Proj- ect Panel, and other reviewers. It is suggested that additional research be conducted to refine the estimated airport curb- side roadway maximum service rates (i.e., the maximum flow rates at each level of service). Performance Measures Curbside utilization is the recommended performance mea- sure for airport curbside roadways. Curbside utilization indi- cates the ability of a roadway to accommodate existing or projected requirements for vehicles loading or unloading at the curbside. It also indicates if spare capacity is available to serve additional demand and surges in demand. Roadway and curbside capacities are typically analyzed for the peak hour or design hour of a facility. For airport road- ways, it is suggested that the design hour be a typical busy hour on the peak day of the week during the peak month. This sug- gestion is in contrast to planning for airfield and other airport facilities, which often considers the peak hour of an average day during the peak month. Typically, a utilization factor of 1.30 or less (65% of the capacity of the curbside loading/unloading lanes) is a desir- able planning target for new curbside roadways. A utilization factor of 1.70 (85% of the combined capacity of the inner and second curbside lanes) is acceptable for existing facilities, rec- ognizing that during peak hours and days of the year, demand will exceed capacity. However, individual airport operator policies regarding parking in multiple lanes may dictate differ- ent utilization factor planning targets. C H A P T E R 5 Evaluating Airport Curbside Operations *Throughout this chapter, the term “parked vehicle” refers to a vehicle that has come to a complete stop and remains stopped to allow the loading or unloading of passengers and their baggage. Vehicles on curbside roadways are not “parked” in the same sense as vehicles in a parking lot or an on-street parking space because these parked vehicles may not be left unattended on airport curbsides. Within the airport industry, vehicles stopped or standing at curbsides are com- monly referred to as parked vehicles.

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

and congestion increase, motorists are required to stop in spaces farther away from their preferred destination. The motorist is required to either stop in a downstream or up- stream curbside space, double park, or, in an extreme case, circle past the curbside area multiple times while searching for an empty space. The key performance measures defining the level of service of an airport curbside roadway are the • Number of vehicles parked or stopped in the curbside lane, and the percent double or triple parked, or otherwise stopped, in a position that interferes with the flow of traf- fic in adjacent lanes. This number of parked vehicles is a function of curbside demand vs. available capacity. • Length and duration of queues at the entrance to the curb- side area. • Average delay encountered by private and commercial vehicles entering and exiting the curbside areas. • Curbside utilization ratio, which is a comparison of the length of the vehicles stopped along the curbside and the effective length of the curbside (i.e., the total length less the space occupied by crosswalks or other areas in which vehicles, or certain classes of vehicles, cannot stop). As stated, most of these measures are obtainable only through microsimulation modeling. Therefore, level-of-service definitions for airport curbside roadways shown in Figure 5-1 and presented in Table 5-2 are based on curbside utilization ratios. These definitions and ratios were validated using focus groups of airline passengers, airport landside managers, and commercial vehicle operators, which were conducted as part of this research project. (Appendix E presents a summary of these focus group sessions.) Estimating Airport Curbside Roadway Traffic Volumes Curbside roadway traffic volumes can be estimated using the same methods used to estimate airport terminal area roadway traffic (see Chapter 3): the traditional four-step travel forecasting method and the growth factors method. The key differences between estimating terminal area road- way traffic and curbside roadway traffic include, for curbside roadway traffic, the need to prepare the following: • Separate estimates of vehicles stopping in a curbside lane and through traffic vehicles. At small airports with a single terminal building and a short curbside area (e.g., less than 500 feet in length), the volume of through vehicles may equal the volume of vehicles stopping at the curbside. However, these volumes may differ at airports having (1) multiple ter- minal buildings or large concourses served by a common roadway, (2) a curbside area with inner and outer curb- side roadways separated by a raised island with midpoint entrances and exits, or (3) curbside roadways that are used by non-curbside traffic (e.g., vehicles entering or exiting parking areas, rental car areas, or other facilities). • Separate analyses of the departures curbside and arrivals curbside roadways. It is necessary to analyze these curb- side areas separately because the departures and arrivals peak periods at an airport (and thus peak periods of curb- side demand) occur during different hours of the day, and vehicle dwell times and space allocations (the proportion of curb length assigned to individual classes of vehicles) differ significantly at the departures and arrivals curbside areas, as described in subsequent sections of this chapter. At airports with dual-level curbside roadways, separate analyses of each level are required. At airports with a single- level curbside roadway, analyses of the peak periods for originating, terminating, and total passengers (originating plus terminating) are required. • Separate analyses for each class of vehicle. Private vehi- cles, taxicabs, limousines, door-to-door vans, courtesy vehi- cles, and charter buses/vans each have different dwell times, required vehicle stall lengths, and maneuvering capabili- ties. Furthermore, each service provided by these vehicles may have different operational methods and be governed by different airport regulations. For example, on an arrivals curbside, an airport operator may permit taxicabs to stand at the curbside for 30 minutes or more to ensure that waiting vehicles are available for arriving customers and may allow charter buses to remain at the curbside for 10 to 15 minutes to ensure that all members of a large party have claimed their bags and boarded the vehicle, but may only allow 43 Performance measure Quick estimation Macroscopic analysis Microsimulation analysis Curbside utilization ratio Number of vehicles parked in second and third lanes Queue length Queuing duration Average vehicle delay Table 5-1. Recommended airport curbside performance measures.

44 Source: LeighFisher. Figure 5-1. Curbside levels of service.

hotel/motel courtesy vehicles to stop while actively board- ing passengers. • Separate estimates of traffic volumes for each terminal building or concourse. The peak periods of activity for each airline serving an airport may occur during different hours of the day. At airports with multiple terminals or large con- course(s) dominated by a single airline, the largest traffic vol- umes (and curbside area requirements) may occur during a different hour (or different 15-minute period) at each termi- nal or near each concourse. In addition, motorists prefer to stop at the curbside area nearest the doors (or skycap podi- ums) serving their airline (or that of the passenger they are transporting). Thus, demands are not distributed uniformly along the length of a curbside—particularly at airports with multiple terminals or large concourses—but are concen- trated at the curbside areas corresponding to the airlines serv- ing the largest volume of passengers during the peak period. As a result, at airports with several terminals or multiple concourses, the traffic volumes and curbside area require- ments that correspond to (or are generated by) each termi- nal or concourse should be estimated. These estimates can be prepared by allocating the total peak-hour traffic vol- umes to each curbside area according to the percentage of total demand served by each area during the peak hour. The percentage of total demand served by each area can be estimated by analyzing (in decreasing order of reliability) the proportion of (1) peak period originating (or terminat- ing) passengers served by each terminal building or con- course, (2) the number of scheduled aircraft seats served by terminal or concourse during the peak period, or (3) the number of aircraft gates served by each concourse. If the data are available, it is preferable to estimate the traf- fic volumes generated by each terminal curbside area (by type of vehicle) separately, as the demographic and/or travel mode choices of the passengers on each airline may differ. For example, the curbside operations at a terminal primarily serv- ing international passengers will differ from curbside opera- tions at a terminal serving regional aircraft or short-haul domestic flights. However, as stated in Chapter 3, such airline passenger data require surveys of airline passengers and are available at few airports. Estimating Airport Curbside Roadway Capacity and Level of Service Estimating airport curbside roadway capacities and levels of service requires analyses of both the curbside lanes and the through lanes because the numbers of vehicles parked in the curbside lanes affect the flow of vehicles in the through lanes; as curbside lanes approach capacity, the capacity of the adja- cent through lanes is reduced. The capacity of a curbside roadway is defined as the smaller of (1) the number of vehicles that can be accommodated in the curbside lane(s) designated for loading or unloading or (2) the volume of through vehicles that can be accommo- dated in the through lanes. 45 Airport curbside levels of service Criteria A B C D E F When double (and triple) parking is allowed at the curbside Maximum demand for curbside standing or parking/effective curbside length (a) 0.90 1.10 1.30 1.70 2.00 >2.00 Maximum service flow rate 5-lane curbside roadway (vph) 3,400 3,280 3,100 2,710 2,400 Up to 2,400 4-lane curbside roadway (vph) 2,830 2,790 2,680 2,220 1,800 Up to 1,800 3-lane curbside roadway (vph) 2,200 1,950 1,580 860 750 Up to 750 When double parking is prohibited at the curbside Maximum demand for curbside standing or parking/effective curbside length (a) 0.70 0.85 1.00 1.20 1.35 >1.35 Maximum service flow rate 4-lane curbside roadway (vph 2,830 2,830 2,800 2,730 2,600 Up to 2,600 3-lane curbside roadway (vph) 2,350 2,250 2,000 1,760 1,600 Up to 1,600 Maximum through lane volume/capacity ratio 0.25 0.40 0.60 0.80 1.00 1.00 vph = vehicles per hour (a) The ratio between the calculated curbside demand and the available effective curbside length. Source: Jacobs Consultancy, November 2009. Table 5-2. Level of service criteria for airport curbside roadways.

Establishing Curbside Lane Capacity Curbside lane capacity is typically estimated in terms of the area (and the number of lanes) that the stopped vehicles may occupy while loading or unloading. Since vehicles stop in a nose-to-tail manner at most airports, this area is described as the effective length of curb measured in linear feet. Effective length is defined as the total length of the lane less (1) any space unavailable for public use because it is reserved for crosswalks, disabled motorists, or specific classes of vehicles (e.g., taxicabs or public buses) and (2) space located beyond the ends of the terminal building or adjacent to columns or other physical bar- riers that discourage its use by motorists because passengers cannot easily open their doors or easily enter/exit a vehicle. The number of stopped vehicles that can be accommo- dated in the curbside lane(s) (i.e., the capacity of the curb- side lanes) varies depending on the number of lanes in which airport operators allow vehicles to routinely stop to load or unload passengers and their baggage. Airport operators establish specific policies concerning double parking that reflect the width of their curbside lanes, enforcement policies and capabilities, customer service, and use by private and/or commercial vehicles. Airports Where Double Parking Is Prohibited At airports where double parking is prohibited, the num- ber of vehicles that can be accommodated in the curbside lane is equal to the effective length of a single curbside lane. Some airport operators restrict curbside parking or standing to a single lane for operational reasons (e.g., a narrow curbside roadway or curbsides used exclusively by commercial vehicles where double parking is prohibited). This description of the number of vehicles that can be accommodated in the curbside lane also applies to curbside roadways with a maximum of three lanes. This is because on a curbside roadway with three lanes only a single through lane would be available if double parking were to occur, which would lead to frequent bottlenecks (e.g., when a double- parked vehicle or an open door of such a vehicle intrudes into the third lane). Thus, a single through/maneuvering lane for a significant portion of the curbside length is considered unacceptable and double parking is generally not tolerated on curbside roadways with a maximum of three lanes. Airports Where Double Parking Is Allowed At airports where double parking is allowed on the curb- side roadways, the number of vehicles that can be accommo- dated at the curbside is equal to twice the effective curbside length. At airports where double parking is regularly allowed, pavement markings typically have been installed designating the lane next to the sidewalk plus the adjacent lane for pas- senger drop-off or pickup, or where enforcement policies allowing double parking have been established. On roadways where double parking is allowed, if the road- way were operating at full capacity, the stopped vehicles would not be evenly distributed along the length of the two curbside lanes, and some motorists would choose to triple park next to the most desirable doorways or other locations. Additional Considerations At airports with inner and outer curbside areas available for use by private vehicles, these areas have different effective capacities, even if they are the same length. Motorists prefer to stop at the most convenient space available (e.g., the inner curbside lane), even if they observe downstream congestion or delays on this roadway. Thus, it is necessary to “discount” the capacity of the outer, less convenient curbside area if both areas are allocated to private vehicles. If one curbside is allo- cated to private vehicles and the second is allocated to com- mercial vehicles, such discounting is not required. For example, motorists approaching the departures curbside at Salt Lake City International Airport can use the curbside area adjacent to the terminal building or an alternative curbside area within the adjacent parking garage. Passengers using the alter- native curbside are provided with a grade-separated path to/ from the terminal building and are offered skycap service on Delta Air Lines. Notwithstanding the good access, good direc- tional signage, and amenities available, motorists are reluctant to use the curbside area within the parking garage, even when the curbside area adjacent to the terminal is congested. Consequently, it is suggested that, when calculating the capacity of a similar curbside configuration at other airports, it is necessary to adjust (or discount) the actual length of curb space within a garage (or other supplemental location) to determine its effective capacity. This adjustment is necessary because, if both the primary and supplemental curbsides are allocated for private vehicle use, the supplemental curbside will provide less capacity (even though it may be the same length) than curb space adjacent to the terminal building because it attracts fewer passengers. This discount factor is similar to operational factors, presented in the 2000 HCM, used to calculate roadway capacity and account for population factors, lane widths, rolling terrain, or unfamiliar drivers. No published research provides guidance on this discount factor, but the factor appears to vary according to the traffic queues caused by downstream congestion, local enforcement policies, availability of skycap service and dynamic signage, and the demographics of the passenger market (e.g., the pro- portion of frequent travelers or those traveling primarily with carry-on baggage). It is suggested that analyses be guided by field observations of existing conditions, which would reflect the unique characteristics of the airport and its passengers. If 46

field data are unavailable, it is suggested that the capacity of the supplemental curb space located in a garage be dis- counted by 50% and that the capacity of an outer curbside be discounted by 20% to 30%. Alternative Curbside Configurations It is assumed in the above discussions that vehicles stop in the curbside lane in nose-to-tail configuration. However, at some airports, the curbside areas are configured with pull-through spaces or 45-degree stalls. (See Chapter 2 for illustrations of alternative curbside configurations.) The above methods are applicable to these configurations with the excep- tion of the sample vehicle dwell times and through-lane capac- ities discussed in the following section. Calculating Curbside Lane Requirements Quick-Estimation Method This method is appropriate for use during the early plan- ning and design stages for a new curbside when little is known about the details of the curbside design or layout. This method is used to compute the curb length required to serve a given demand, but it does not provide specific results on perfor- mance, such as average delay or queuing probability. A curbside lane can be considered as a series of stopping spaces, each capable of accommodating one vehicle. The aver- age number of vehicles each space can serve during a given time period is inversely proportional to the average length of time (referred to as the vehicle dwell time) a vehicle occupies a space. For example, if the average vehicle dwell time is 3 min- utes, then each space can accommodate, on average, 20 vehi- cles per hour. If the peak-hour volume is 160 vehicles, then (with the assumed average dwell time of 3 minutes per vehicle), the required curbside length is equivalent to eight spaces or 200 linear feet (assuming an average space length of 25 feet for illus- trative purposes). This can be represented mathematically as where Ra = the average curbside length required to accommodate the vehicles stopping at a curbside area. V = the hourly volume of vehicles stopping at a curbside area. Di = the average vehicle dwell time (in minutes). L = the average vehicle stall length. This formula represents a condition where a single class of vehicles is using a curbside area (e.g., a curbside serving pri- vate vehicles exclusively), or where the requirements are developed assuming that all vehicles can be represented using average dwell times and a single stall length. More accurate R V D La i=  60 estimates can be developed by considering, separately for each class of vehicle, the hourly volume, the distribution of dwell times (rather than average dwell time), and average vehicle length. Additional accuracy can result from consideration of the peak periods within the peak hour (e.g., analysis of the peak 15 or 20 minutes) and the nonuniform distribution of demand along the curbside lane caused by a concentration of traffic at specific airline doors or other attraction points. The nonuniform arrival rate and distribution of vehicles can be reflected using statistical factors (e.g., a Poisson distribution). Table 5-3 presents data, gathered at the airports serving Memphis, Oakland, Portland, San Francisco, and Washington, D.C. (Dulles), used to calculate curbside lane requirements by class of vehicle, the application of a Poisson distribution (or adjustment) factor, and the resulting curbside require- ments. The table presents examples of average curbside dwell times and vehicle stall lengths based on observations of post- 2001 curbside roadway operations at the airports, the estimated curbside requirements (i.e., design length) for five zones (two zones on the enplaning curbside and two zones plus a cour- tesy vehicle lane on the deplaning curbside). A comparison of the estimated requirements with the available curb length yields utilization factors for each of the five zones. As shown, two of the zones are substantially over capacity as evidenced by the utilization factors over 2.0. The quick-estimation method involves the following steps: 1. Determine peak-hour traffic volume from field survey or estimates of future traffic. 2. Determine the vehicle mix. If vehicle mix is unknown, assume that private vehicles represent 70% to 80% of the total traffic volumes, taxicabs and limousines represent 5% to 10%, courtesy vehicles represent 5% to 10%, and vans/buses/public transit represent 5%. 3. Determine the average vehicle stall length. Use the de facto values shown in Table 5-3 or the QATAR model (see Fig- ure 5-3) or measure representative values, particularly for unusual vehicles or atypical parking configurations. 4. Determine vehicle dwell times using field measurements or the de facto dwell times shown in Table 5-3 or the QATAR model (see Figure 5-3). 5. Calculate curbside stall requirements that are equal to the volume multiplied by vehicle dwell times divided by 60 minutes. 6. Determine curbside design stall requirements that are equal to the curbside stall requirements times a probabilistic factor applied to the total curbside stall requirements (if a mixed-use curbside such as a typical departures curbside) or to an individual class of vehicles (if curb space is allo- cated to this classification), ranging from 3.0 for require- ments less than 5 curbside stalls to 1.2 for curbside stall requirements of 100 or more. 47

7. Determine curbside design length that is equal to the number of design stalls times the average vehicle stall length 8. Calculate the utilization factor that is equal to the curbside design length divided by the existing curb capacity (or effective length) considering whether double parking is allowed by the airport operator. As defined previously in this chapter, a curbside utilization factor equal to or less than 1.3 is considered acceptable for a new design, while a utilization factor equal to or less than 1.7 is considered acceptable for existing curbside roadways. Macroscopic Method Alternatively, the curbside lane can be considered a series of processing points (or servers) and traditional queuing analy- ses can be used to calculate the capacity of individual servers and the total capacity of the curbside lane. The macroscopic method (QATAR) described in the upcoming section on Ana- lytical Framework Hierarchy for Airport Curbside Roadways uses queuing analysis to estimate curbside capacity. The following subsections describe the calculations of through-lane capacity and curbside capacity. Calculating Through-Lane Requirements The requirements for curbside roadway through lanes depend on the areas they serve. At airports with a single ter- minal building and a short curbside area, the volume of through vehicles may equal the volume of vehicles stopping at the curbside. As discussed in previous chapters, factors that may result in higher volumes of traffic in the through lanes include vehicles bypassing a curbside area (1) that does not serve their airline (e.g., a different terminal building or major 48 Mode Hourly volume (vph) Average curbside dwell time (minutes) Required curbside stalls Required design stalls (a) Vehicle stall length (feet) Design length (feet) Existing curb length (feet) Curbside utili- zation factor Enplaning level, north Private vehicles 621 3 31.0 40 25 1,000 Taxicabs 52 2 2.0 5 25 125 Limousines 9 2.5 0.4 2 30 60 Door-to-door vans (b) 38 3 1.9 3 30 90 Courtesy vans (b) 24 4 1.6 3 30 90 Scheduled buses (b) 10 5 0.8 1 50 50 Total 754 1,415 600 2.36 Enplaning level, south Private vehicles 363 3 18.0 25 25 625 Taxicabs 35 2 1.0 3 25 75 Limousines 6 2.5 0.3 1 30 30 Door-to-door vans (b) 38 3 1.9 2 30 60 Courtesy vans (b) 24 4 1.6 3 30 90 Scheduled buses (b) 10 5 0.8 1 50 50 Total 476 930 830 1.12 Deplaning level, north Private vehicles 580 5.2 50.0 62 25 1,550 Limousines 5 5.2 0.4 1 30 30 Total 585 1,580 535 2.95 Deplaning level, south Private vehicles 345 5.2 30.0 39 25 975 Limousines 4 5.2 0.3 1 30 30 Total 349 1,005 780 1.29 Deplaning level courtesy vehicle lane Courtesy vehicles (b) 223 1 4 8 30 240 300 0.80 (a) Represents calculated stall requirements adjusted to reflect random arrival of vehicles and nonuniform distribution of traffic volumes and demands using Poisson statistical probability factors. (b) Assumes that this mode makes a single stop at the curbside. Source: LeighFisher, November 2009. Table 5-3. Estimate of terminal building curbside requirements—sample calculation.

concourse), (2) that is reserved for other classes of vehicles (e.g., authorized commercial vehicles), or (3) to enter or exit parking, rental car, or other land uses not related to curbside activities. As noted, bypass traffic proceeding to another terminal (as opposed to through traffic proceeding to a downstream portion of the curbside lane) may represent a significant portion of the total curbside roadway traffic vol- ume. When these conditions occur, it is necessary to use the methods described in Chapter 4 to estimate the volume of traffic associated with the alternative land uses and/or to assign traffic volumes to each curbside roadway section (or airline) and class of vehicle. The capacity of a curbside roadway through lane is mea- sured using methods similar to those described in Chapter 4 for other airport terminal area roadways, adjusted to account for the presence of double- or triple-parked vehicles. As noted previously, double- and triple-parked vehicles block or delay the movement of vehicles in through lanes, because through traffic must decelerate and maneuver around these stopped vehicles. As a result, through-lane capacity decreases when curbside lane demand exceeds the available capacity of a spe- cific curbside segment (as opposed to the entire curbside length), and vehicles are double or triple parked. The reduction in through-lane capacity resulting from increased curbside lane demand can be estimated using com- mercially available microsimulation models capable of simu- lating airport curbside roadways or using QATAR (discussed later in this chapter). Alternatively, the approximations shown in Table 5-2 can be used to estimate curbside roadway lane capacities. Curbside roadway capacity must also be reduced when at- grade pedestrian crosswalks are present. The extent of the capacity reduction is a function of the volume of pedestrians crossing the roadway since the amount of time motorists must wait for pedestrians increases with pedestrian traffic. For example, if a crosswalk is controlled by a traffic signal, and if the signal allocates 25% of the green time during each hour to pedestrians, then capacity of the curbside roadway would be 25% less than if there were no crosswalk. If, instead of a signal, crosswalk operations are controlled by a traffic control officer, then a similar approximation can be made by observing curbside roadway operations. If the crosswalk is uncontrolled, then the behavior of motorists (do they stop when a pedestrian enters a crosswalk?) and the volume of pedestrians need be considered. Additional Considerations in Estimating Commercial Ground Transportation Vehicle Curbside Requirements The analytical methods used to estimate curbside traffic volumes presented in Chapter 4 are applicable to private vehicles and commercial ground transportation vehicles, the volumes of which can be directly correlated to airline passenger demand (e.g., limousines, taxicabs, and door-to- door vans dropping off passengers). However, these analyt- ical methods are not applicable to vehicles that are allowed to remain at the curbside for extended periods (e.g., taxicabs and door-to-door vans standing in queues waiting to pick up passengers) or that operate on a scheduled or de facto scheduled basis (e.g., courtesy vehicles that generally oper- ate on fixed headways regardless of the number of passen- gers transported). Allocation of Curb Space Generally, airport operators do not reserve space for com- mercial ground transportation vehicles dropping off airline passengers, with the exception of vehicles, such as public buses, that drop off and pick up passengers at the same curb- side space. The amount of space allocated to commercial ground transportation vehicles picking up passengers is gen- erally determined by airport management considering such factors as • Customer expectations. Deplaning airline passengers gen- erally expect taxicabs to be available immediately adjacent to the baggage claim area, or visible from the exit doors. Passengers who have reserved luxury limousines expect a higher level of service than those choosing public trans- portation (e.g., baggage assistance, shorter walking times, minimal wait time). • Operational needs. To minimize the wait times of deplan- ing passengers, taxicabs are generally allowed to wait at the deplaning curbside area in queues of 3 to 10 vehicles. The number of taxicabs in the queue is a function of airport policy, the proximity of a taxicab hold area (where addi- tional taxicabs may wait until dispatched to the curb), and the availability of curb space. Similarly, door-to-door vans are generally allowed to wait at the deplaning curbside, with the number of vans a function of the number of regional destinations served, number of van companies, airport policies, and available curb space. • Space requirements. In analyzing the amount of space to be allocated to each class of commercial vehicle operator (e.g., hotel/motel courtesy vehicles), the number of vehi- cles that will use the space concurrently (which is based on the number of operators and the frequency with which they serve the airport), and the permitted vehicle dwell times and vehicle sizes must be considered. • Vehicle maneuverability. In determining the amount of curb space to be allocated to each class of commercial vehi- cle operator, consideration should be given to the maneu- verability requirement of the vehicles used (e.g., vans, 49

minibuses, or full-size buses) and, if appropriate, require- ments of access to baggage compartments or baggage trucks. For example, a 45-foot-long full-size bus requires about 60 feet to stop parallel to a curb space. If a bus has an under-the-floor baggage storage compartment, curb spaces should be configured so that columns, sign poles, or other obstacles do not interfere with the opening of the baggage compartment. • Vertical clearances. The ability of a full-size bus or other large vehicle to use a curbside area may be limited by the vertical clearance available (including low-hanging signs or drainage structures). For example, the minimum vertical clearances required are 13 feet for a full-size bus, 11.5 feet for the shuttle buses used by rental car companies, and 9 feet to 10 feet for courtesy vans serving hotels/motels. These dimensions can vary for those vehicles using com- pressed natural gas, having rooftop air conditioners, or having rooftop antennae. Some multilevel roadways can not accommodate full-size buses or over-the-road coaches used by charter bus operators. • Competition. Commercial vehicle operators compete with private vehicles, other operators providing the same service, and operators providing services that are per- ceived as being similar (e.g., taxicab and door-to-door van operators). Each commercial vehicle operator gener- ally wishes to be assigned space nearest the busiest termi- nal exit doors or space that is equivalent to or near the space provided to their competitors to maintain a “level playing field.” • Airport management policy. Some airport operators have policies that encourage the use of public transportation and, thus, assign public transit vehicles the most conve- nient or most visible curb space. • Revenues generated by commercial vehicle operations. Airport operators receive significant revenues from public parking and rental car concessions. As such, the courtesy vehicles serving on-airport parking lots and rental car facil- ities may be assigned higher priorities than other courtesy vehicles, including those serving privately operated park- ing or rental car facilities located off airport. Number of Curbside Stops Made by Commercial Vehicles An additional factor to be considered when estimating the curbside roadway lane requirements of commercial vehicles is the number of stops each vehicle makes. For example, a sin- gle courtesy vehicle or public bus may stop two or more times along a terminal curbside, depending on the length of the curb and airport policies. The calculation of curbside lane requirements for each courtesy vehicle, for example, must be adjusted to account for the number of stops. Analytical Framework Hierarchy for Airport Curbside Roadways Airport curbside roadway operations—particularly the reduction in through-lane capacity that results from increased curbside lane demand—can be analyzed using the quick- estimation method described below, the macroscopic method (QATAR) described in subsequent sections, or commercially available microsimulation methods used to simulate airport curbside roadways. Quick-Estimation Method The quick-estimation method is used to measure both the curbside utilization factor (i.e., the ratio between curbside demand and curbside capacity) and the maximum through- put rate for five-, four-, and three-lane curbside roadways. The level of service for a curbside roadway is defined as the worst result of these two measures. Estimates of the maximum flow rates (i.e., service flow rates) on curbside roadways at each level of service can be determined using the data provided in Table 5-2. These data were established from observations of curbside traffic flows conducted as part of this research project and analyses of curb- side roadway traffic flows conducted using microsimulation of airport roadway traffic. Figure 5-2 depicts the relationship between curbside roadway traffic flow rates and utilization factors for five-, four- and three-lane curbside roadways. Since as used in Table 5-2, “capacity” varies depending on whether an airport operator allows vehicles to double or single park, the policy of the airport being analyzed should be reviewed. To establish the level of service for a given curbside demand and traffic volume, the data in Table 5-2 should be used as follows: 1. Calculate the curbside utilization factor. 2. Select the corresponding utilization factor for the curbside lane as shown in Table 5-2, rounding up to the next near- est value, and note the corresponding level of service. For example, for a four-lane curbside roadway with a calcu- lated ratio of 0.6, the level of service is C. 3. Calculate the level of service for the through lanes by (1) selecting the maximum service flow rate row in the table corresponding to the appropriate number of lanes on the entire curbside roadway (include all curbside lanes and through lanes), and (2) comparing this rate to the volume of traffic on the curbside to calculate the volume/capacity ratio. For example, the roadway capacity is 2,680 vehicles per hour for a four-lane roadway with curbside lanes oper- ating at LOS C. If this roadway were serving 2,500 vehicles per hour, it would have a v/c ratio of 2,500/2,680 or 0.93. 50

4. Use Table 5-2 to determine the level of service that corre- sponds to the calculated v/c ratio for the through lanes. A v/c ratio of 0.93 corresponds to LOS E. 5. The level of service for the entire curbside roadway (sys- tem) is determined by the component—either the curb- side lane or the through lanes—with the poorest level of service. Considering the above example, if the curbside utilization factor corresponds to LOS C and the peak hour traffic volume corresponds to LOS E, the level of service for the curbside roadway is LOS E. The maximum service flow rates shown in Table 5-2 apply to all vehicles on the curbside roadway, including those stopped in the curbside lane. These flow rates need not be adjusted for heavy vehicles or driver familiarity because they were developed from observations of traffic operations on airport curbside roadways. Macroscopic Model—Quick Analysis Tool for Airport Roadways Developed through this research project QATAR allows airport planners and operators to determine the ability of a curbside roadway to accommodate changes in traffic volumes, airline passenger activity, vehicle mix, curbside allocation plans, and curbside enforcement levels. QATAR also allows the user to observe how airport curbside roadway levels of service are expected to vary as these input factors change. Appendix G presents additional information on the method- ology and mathematics used in QATAR. In the analysis procedure used in QATAR, it is assumed that (1) vehicles begin to double park and potentially triple park, if allowed, as the number of vehicles stopping in a zone approaches the zone’s capacity (or length), and (2) the capacity of the adjacent maneuver and travel lanes decreases as the number of double- and triple-parked vehicles increases. The propensity of arriving vehicles to double park (reflect- ing the percentage of occupied curbside spaces) can be modified by the QATAR user to reflect local conditions and policies. Using a multiserver (or multi-channel) queuing model, QATAR calculates • The number of vehicles stopping in each curbside zone to drop off or pick up passengers. The number of spaces occupied simultaneously (assuming a 95% probability), 51 Source: Jacobs Consultancy, November 2009. Figure 5-2. Curbside roadway capacity reduction curves.

when compared to the number of available spaces, defines the level of service for the curbside lane. • The number of bypass vehicles proceeding to/from adjacent zones. The number of bypass vehicles, when compared to the capacity of the bypass lanes, defines the level of service for the bypass lanes. The capacity of the bypass lanes is determined by the number of travel lanes and the level of service of the curbside lane. As described previously, a reduction in curbside level of service (i.e., an increase in the amount of double and triple parking) causes a reduction in the capacity of the bypass lanes. • The peaking characteristics of the roadways, assuming that the volumes will not be exceeded 95% of the time during the analysis period. Traffic volumes on curbside roadways are not uniform throughout an hour-long period, or other analysis period, and peak periods of activity or microbursts of traffic occur frequently. Inputs Figure 5-3 presents an example of a QATAR input sheet (including the suggested default values for dwell times and vehicle stall lengths). As shown, the following information is required to use QATAR: • Curbside geometry—The physical characteristics of the curbside, including length, number of lanes, and number of roadway lanes approaching the curbside area. If the user 52 Figure 5-3. Example of QATAR input sheet.

wishes to divide the curbside into zones, the length of each zone must be defined first. • Hourly traffic volumes—The existing hourly volume of vehicles entering the curbside. If a future curbside condi- tion is to be analyzed, the traffic volumes should be adjusted to reflect future growth. QATAR allows the user to apply a growth factor to existing traffic volumes. • Through vs. curbside traffic volumes—The proportion of vehicles using the roadway that stop at the curbside. If the user has divided the curbside into zones, the propor- tion (or volume) of vehicles stopping in each zone is required. • Vehicle mix—The mix (i.e., classification) of vehicles in the traffic stream entering the curbside (either the actual volume or the percent of vehicles by vehicle classification). If the user has divided the curbside into zones, the propor- tion (or volume) of vehicles by classification stopping in each zone is required, or the user can determine that the proportion is constant in each zone. • Dwell times—The user can accept the default values in QATAR or enter vehicle dwell times by vehicle classification. • Vehicle stall length—The user can accept the default val- ues in QATAR or enter vehicle stall lengths by vehicle classification. • Adjustment factors—The user can enter adjustment fac- tors in QATAR to reflect the effect of pedestrian cross- walks, regional conditions/driver behavior, and a weight- ing/calibration factor. Outputs Figure 5-4 presents an example of a QATAR output sheet. As shown, QATAR yields the following outputs: • Level of service—A graphic depicting the levels of service for the curbside areas and roadway through lanes in each zone. • Volume/capacity ratio—A tabular presentation of the volume/capacity ratio for the through lanes in each zone. • Curbside utilization ratio—A tabular presentation of the curbside utilization ratio for the curbside area in each zone. In some cases, the capacity of the roadway approaching the curbside may dictate the capacity of the curbside roadway seg- ment. For example, the capacity of a five-lane curbside section with a two-lane approach roadway is governed by the ability of the approach roadway to deliver vehicles to the curbside. Limitations of the Analysis Tool QATAR is used to analyze the macroscopic flow of vehicles but not the operation of individual vehicles (as would a road- way traffic microsimulation model). As such, QATAR does not 53 Figure 5-4. Example of QATAR output sheet.

• Replicate or analyze operations, such as individual vehicles maneuvering into or out of curbside spaces, improperly parked vehicles, vehicle acceleration/deceleration character- istics, or how these characteristics vary by vehicle size or type. • Analyze how roadway congestion or queues affect traffic operations in the zones located upstream of those being analyzed, or meter (i.e., restrict) the flow of vehicles into downstream zones. • Represent pedestrians crossing a curbside roadway (prop- erly or improperly) or vehicle delays caused by pedestrian activity other than to allow the user to estimate the approx- imate decrease in roadway capacity. • Evaluate the potential capacity decreases of specific curb- side geometries. Rather, a single, continuous, linear curb- side roadway is assumed in the model. If the curbside roadway consists of one or more parallel curbside road- ways, QATAR should be used to analyze each parallel curb- side roadway separately. • Consider any upstream or downstream congestion; rather, each zone is treated separately. In reality, a very congested section or loading zone could affect adjacent zones both upstream and downstream. The model does not capture any interaction between zones. As such, QATAR produces an approximation of airport curbside roadway operations. If more detailed analyses are desired, the user is encouraged to use a microsimulation model capable of simulating airport curbside traffic operations. Interpreting the Results Certain vehicles (e.g., courtesy vehicles or door-to-door vans) may make multiple stops along the terminal curbside area, especially at large airports. Vehicles making multiple stops can be represented properly (using Option C—one of the available input sheet options in QATAR) because the total volumes of vehicles stopping in each zone need not equate to the total curbside roadway traffic. However, with Option C, QATAR requires percentages of vehicles to sum to 100% and vehicles making multiple stops may not be accurately repre- sented, particularly if they account for a significant percent- age of the total vehicles entering the roadway. Use of Microsimulation Models Chapter 4 provides guidance on the use of microsimula- tion models for analysis of airport roadways. Based on research team reviews of commercially available microsimulation soft- ware packages commonly used (as of 2008), it was determined that all are capable of adequately modeling the noncurbside terminal area roadways and low-speed weaving and merging maneuvers typically found on airports. However, not all soft- ware packages available at the time of the research team’s review were capable of modeling parking maneuvers or inter- actions between vehicles entering and exiting curbside parking spaces and adjacent through vehicles, or permitted vehicles to double or triple park. It is suggested that the capability of a software package be confirmed prior to considering its use in analyzing airport curbside roadway operations. The following guidance is provided on calibrating a microsimulation model for airport curbside roadways: • If double or triple parking is allowed, verify that the model correctly predicts the average number of double and triple parkers during the peak hour (compare one-hour model simulation to one-hour field counts). • If queuing occurs on the existing curbside roadway, count the throughput in the through lanes and the number of vehicles processed per hour in the curbside lanes under such congested conditions. – Validate through-lane flow rates. Enter demands into the simulation model and verify that the maximum through- lane flow rate for the peak hour predicted by the model matches the field counts. Adjust mean headways in the model until the model through-lane volumes match the field counts. A difference of 5% to 10% between model through-lane volumes and field counts is acceptable. – Validate curbside processing capacity. Enter demands in the simulation model and compare the curbside pro- cessing rate to field counts. Adjust average dwell times in the model until the processing rate over the peak hour matches the field counts. This guidance is in addition to guidance published elsewhere (see FHWA guide on microsimulation model validation). Curbside Performance Measures for Analyses Performed Using Microsimulation The performance measures presented in Table 5-1 are intended to help select the appropriate curbside analysis method. When curbside roadways are analyzed using micro- simulation methods, the performance measures presented in Table 5-2 can be used to compare curbside roadway alternatives in the context of level of service. The measures listed in Table 5-1 do not directly corre- spond to quantitative values equaling a specific level of ser- vice. For example, duration of queuing is a potentially useful measure in the context of comparing alternatives (e.g., if one curbside roadway alternative would result in 2 hours of queu- ing, while another would result in 1 hour of queuing), but the 54

magnitude of the queuing itself could be relatively minor, so reporting an LOS C result for one alternative and an LOS D result for the other could be misleading. Similarly, the queue length measure can provide an easy way to compare alterna- tives, but a relatively long queue could be a better condition than a relatively short queue if the rate at which vehicles are served at the curbside is relatively high for the alternative with the longer queue. Together, length of vehicle queues and average speed— two measures that are typically microsimulation software outputs—can provide a time in queue measure that can be used to compare and evaluate analyses of curbside roadway prepared using microsimulation models. Because of the wide range of motorist expectations regarding traffic conditions when they arrive at an airport curbside, a range of thresholds for time in queue between acceptable and unacceptable oper- ations were identified, with unacceptable operations corre- sponding to the threshold between LOS E and LOS F. For the lowest of these thresholds, the time in queue was identified as 60 seconds. This time (60 seconds) is consistent with the LOS E/F threshold for unsignalized and signalized intersections and considered to be a reasonable lower threshold. For con- text, consider a small-hub airport, such as Billings Logan International Airport. Most of the time, there is no queue leading to this airport’s curbside, even during peak periods in bad weather. If a queue did develop such that motorists would have to be in the queue for 60 seconds, it would seem unacceptable in that context. For the upper bound of acceptable/unacceptable thresh- olds, a comment expressed in at least one focus group con- ducted for this research project—moving is acceptable, not moving is not acceptable—was used. From a motorist’s per- spective, it would seem as if a queue were not moving if a per- son could walk faster than the vehicles were moving. Using an arbitrary queue length of one mile and brisk walking speeds of 3 to 4 mph, the time spent in such a queue would be 20 and 15 minutes, respectively. The 20-minute time in queue appears to be a reasonable upper bound for a threshold between accept- able and unacceptable (anecdotal experience suggests that queues of this length likely occur at large airports somewhat regularly). This time in queue is not intended to represent the longest queue time during the busiest days of a year, when delays may be even greater. Also, higher values of time in queue could be used by airport operators who observe higher thresh- olds at their locations. Service thresholds corresponding to LOS A have also been defined. It is suggested that time in queue should not be zero, but should seem to a motorist as if it were nearly zero. A simple way to identify an LOS A value would be to take 10% of the LOS E/F value, which is close to the LOS A/B threshold for delay at signalized intersections defined in the HCM. For the LOS E/F threshold of 60 seconds, a time in queue of 6 seconds or less would correspond to LOS A— from a practical perspective, that would essentially mean no queue or perhaps one vehicle waiting, which is consistent with the original basis for this threshold. With an LOS E/F threshold set at 20 minutes, the LOS A time in queue would, therefore, be 120 seconds. Although 120 seconds in a queue seems high compared to, for example, a signalized intersection delay, for a motorist approaching a curbside anticipating a wait of up to 20 minutes, a 2-minute wait would seem remark- ably short. Once the upper and lower level-of-service bounds are identified, the values for the other LOS values can be calcu- lated using a straight-line projection between the two points. The results of these estimates, assumptions, and calculations are presented in Table 5-4. The information can also be pre- sented in graph form, as shown on Figure 5-5. As noted, the values of the time in queue can easily be extrapolated upward from the 20-minute level to any value. 55 Small-hub and smaller medium- hub airports (a) Large medium-hub and large-hub airports (a) Given maximum acceptable time spent in queue in seconds (a) Level of service 60 120 300 600 900 1,200 Maximum for LOS E 60 120 300 600 900 1,200 Maximum for LOS D 47 93 233 465 698 930 Maximum for LOS C 33 66 165 330 495 660 Maximum for LOS B 20 39 98 195 293 390 Maximum for LOS A 6 12 30 60 90 120 Notes: *Input data are to be taken from microsimulation modeling output. (a) Analyst must first select a value for the maximum acceptable time spent in queue for the subject airport. Then, using queue length and average speed outputs from the microsimulation model, the level of service can be identified. Table 5-4. Time spent in queue for levels of service.*

56 0 200 400 600 800 1000 1200 1400 60 120 300 600 900 1800 Maximum Tolerable Time in Queue (sec) Ti m e in Q ue ue (s ec ) Max for LOS E Max for LOS D Max for LOS C Max for LOS B Max for LOS A Note: Analyst must first select a value for the maximum acceptable time spent in queue for the subject airport. Then, using queue length and average speed outputs from the microsimulation model, the level of service can be identified. Figure 5-5. Time spent in queue for levels of service, large medium-hub and large-hub airports (input data to be taken from microsimulation modeling output).

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TRB’s Airport Cooperative Research Program (ACRP) Report 40: Airport Curbside and Terminal Area Roadway Operations includes guidance on a cohesive approach to analyzing traffic operations on airport curbside and terminal area roadways.

The report examines operational performance measures for airport curbside and terminal area roadway operations and reviews methods of estimating those performance measures. The report includes a quick analysis tool for curbside operations and low-speed roadway weaving area, highlights techniques for estimating traffic volumes, and presents common ways of addressing operational problems.

Appendix A, Glossary, to ACRP Report 40 is included in the printed report. Appendices B through G, are available online and listed below:

Appendix B: Bibliography

Appendix C: Summary of Terminal Area Roadway Traffic Volume Surveys

Appendix D: Summary of Curbside Roadway Characteristic Surveys

Appendix E: Summary of Focus Group Surveys

Appendix F: A Reproduction of Portions of TRB Circular 212

Appendix G: Overview of QATAR Curbside Analysis Methodology

Link to QATAR Curbside Analysis Methodology

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