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

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

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

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

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

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

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56 1400 1200 1000 Time in Queue (sec) Max for LOS E 800 Max for LOS D Max for LOS C 600 Max for LOS B Max for LOS A 400 200 0 60 120 300 600 900 1800 Maximum Tolerable Time in Queue (sec) 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).