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45 Table 5-2. Level of service criteria for airport curbside roadways. 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. hotel/motel courtesy vehicles to stop while actively board- terminal or concourse during the peak period, or (3) the ing passengers. number of aircraft gates served by each concourse. Separate estimates of traffic volumes for each terminal building or concourse. The peak periods of activity for each If the data are available, it is preferable to estimate the traf- airline serving an airport may occur during different hours of fic volumes generated by each terminal curbside area (by type the day. At airports with multiple terminals or large con- of vehicle) separately, as the demographic and/or travel mode course(s) dominated by a single airline, the largest traffic vol- choices of the passengers on each airline may differ. For umes (and curbside area requirements) may occur during a example, the curbside operations at a terminal primarily serv- different hour (or different 15-minute period) at each termi- ing international passengers will differ from curbside opera- nal or near each concourse. In addition, motorists prefer to tions at a terminal serving regional aircraft or short-haul stop at the curbside area nearest the doors (or skycap podi- domestic flights. However, as stated in Chapter 3, such airline ums) serving their airline (or that of the passenger they are passenger data require surveys of airline passengers and are transporting). Thus, demands are not distributed uniformly available at few airports. along the length of a curbside--particularly at airports with multiple terminals or large concourses--but are concen- Estimating Airport Curbside trated at the curbside areas corresponding to the airlines serv- Roadway Capacity and ing the largest volume of passengers during the peak period. Level of Service As a result, at airports with several terminals or multiple concourses, the traffic volumes and curbside area require- Estimating airport curbside roadway capacities and levels ments that correspond to (or are generated by) each termi- of service requires analyses of both the curbside lanes and the nal or concourse should be estimated. These estimates can through lanes because the numbers of vehicles parked in the be prepared by allocating the total peak-hour traffic vol- curbside lanes affect the flow of vehicles in the through lanes; umes to each curbside area according to the percentage of as curbside lanes approach capacity, the capacity of the adja- total demand served by each area during the peak hour. cent through lanes is reduced. The percentage of total demand served by each area can be The capacity of a curbside roadway is defined as the smaller estimated by analyzing (in decreasing order of reliability) of (1) the number of vehicles that can be accommodated in the proportion of (1) peak period originating (or terminat- the curbside lane(s) designated for loading or unloading or ing) passengers served by each terminal building or con- (2) the volume of through vehicles that can be accommo- course, (2) the number of scheduled aircraft seats served by dated in the through lanes.

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46 Establishing Curbside Lane Capacity senger drop-off or pickup, or where enforcement policies allowing double parking have been established. Curbside lane capacity is typically estimated in terms of the On roadways where double parking is allowed, if the road- area (and the number of lanes) that the stopped vehicles may way were operating at full capacity, the stopped vehicles would occupy while loading or unloading. Since vehicles stop in a not be evenly distributed along the length of the two curbside nose-to-tail manner at most airports, this area is described as lanes, and some motorists would choose to triple park next to the effective length of curb measured in linear feet. Effective the most desirable doorways or other locations. 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 Additional Considerations or public buses) and (2) space located beyond the ends of the At airports with inner and outer curbside areas available terminal building or adjacent to columns or other physical bar- for use by private vehicles, these areas have different effective riers that discourage its use by motorists because passengers capacities, even if they are the same length. Motorists prefer cannot easily open their doors or easily enter/exit a vehicle. to stop at the most convenient space available (e.g., the inner The number of stopped vehicles that can be accommo- curbside lane), even if they observe downstream congestion dated in the curbside lane(s) (i.e., the capacity of the curb- or delays on this roadway. Thus, it is necessary to "discount" side lanes) varies depending on the number of lanes in which airport operators allow vehicles to routinely stop to load the capacity of the outer, less convenient curbside area if both or unload passengers and their baggage. Airport operators areas are allocated to private vehicles. If one curbside is allo- establish specific policies concerning double parking that cated to private vehicles and the second is allocated to com- reflect the width of their curbside lanes, enforcement policies mercial vehicles, such discounting is not required. and capabilities, customer service, and use by private and/or For example, motorists approaching the departures curbside commercial vehicles. 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- Airports Where Double Parking Is Prohibited native curbside are provided with a grade-separated path to/ At airports where double parking is prohibited, the num- from the terminal building and are offered skycap service on ber of vehicles that can be accommodated in the curbside lane Delta Air Lines. Notwithstanding the good access, good direc- is equal to the effective length of a single curbside lane. Some tional signage, and amenities available, motorists are reluctant airport operators restrict curbside parking or standing to a to use the curbside area within the parking garage, even when single lane for operational reasons (e.g., a narrow curbside the curbside area adjacent to the terminal is congested. roadway or curbsides used exclusively by commercial vehicles Consequently, it is suggested that, when calculating the where double parking is prohibited). capacity of a similar curbside configuration at other airports, This description of the number of vehicles that can be it is necessary to adjust (or discount) the actual length of curb accommodated in the curbside lane also applies to curbside space within a garage (or other supplemental location) to roadways with a maximum of three lanes. This is because on determine its effective capacity. This adjustment is necessary a curbside roadway with three lanes only a single through lane because, if both the primary and supplemental curbsides are would be available if double parking were to occur, which allocated for private vehicle use, the supplemental curbside would lead to frequent bottlenecks (e.g., when a double- will provide less capacity (even though it may be the same parked vehicle or an open door of such a vehicle intrudes into length) than curb space adjacent to the terminal building the third lane). Thus, a single through/maneuvering lane for because it attracts fewer passengers. This discount factor is a significant portion of the curbside length is considered similar to operational factors, presented in the 2000 HCM, unacceptable and double parking is generally not tolerated on used to calculate roadway capacity and account for population curbside roadways with a maximum of three lanes. 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 Airports Where Double Parking Is Allowed queues caused by downstream congestion, local enforcement At airports where double parking is allowed on the curb- policies, availability of skycap service and dynamic signage, side roadways, the number of vehicles that can be accommo- and the demographics of the passenger market (e.g., the pro- dated at the curbside is equal to twice the effective curbside portion of frequent travelers or those traveling primarily with length. At airports where double parking is regularly allowed, carry-on baggage). It is suggested that analyses be guided by pavement markings typically have been installed designating field observations of existing conditions, which would reflect the lane next to the sidewalk plus the adjacent lane for pas- the unique characteristics of the airport and its passengers. If

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

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48 Table 5-3. Estimate of terminal building curbside requirements--sample calculation. Average Vehicle Existing Curbside Hourly curbside Required Required stall Design curb utili- volume dwell time curbside design stalls length length length zation Mode (vph) (minutes) stalls (a) (feet) (feet) (feet) 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. 7. Determine curbside design length that is equal to the and the total capacity of the curbside lane. The macroscopic number of design stalls times the average vehicle stall method (QATAR) described in the upcoming section on Ana- length lytical Framework Hierarchy for Airport Curbside Roadways 8. Calculate the utilization factor that is equal to the curbside uses queuing analysis to estimate curbside capacity. design length divided by the existing curb capacity (or The following subsections describe the calculations of effective length) considering whether double parking is through-lane capacity and curbside capacity. allowed by the airport operator. As defined previously in this chapter, a curbside utilization factor equal to or less Calculating Through-Lane Requirements than 1.3 is considered acceptable for a new design, while a utilization factor equal to or less than 1.7 is considered The requirements for curbside roadway through lanes acceptable for existing curbside roadways. 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 Macroscopic Method at the curbside. As discussed in previous chapters, factors that Alternatively, the curbside lane can be considered a series of may result in higher volumes of traffic in the through lanes processing points (or servers) and traditional queuing analy- include vehicles bypassing a curbside area (1) that does not ses can be used to calculate the capacity of individual servers serve their airline (e.g., a different terminal building or major

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