National Academies Press: OpenBook

Airport Curbside and Terminal Area Roadway Operations (2010)

Chapter: Chapter 2 - Framework for Analysis of Airport Roadways and Curbsides

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Suggested Citation:"Chapter 2 - Framework for Analysis of Airport Roadways and Curbsides." 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 2 - Framework for Analysis of Airport Roadways and Curbsides." 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 2 - Framework for Analysis of Airport Roadways and Curbsides." 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 2 - Framework for Analysis of Airport Roadways and Curbsides." 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 2 - Framework for Analysis of Airport Roadways and Curbsides." 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 2 - Framework for Analysis of Airport Roadways and Curbsides." 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 2 - Framework for Analysis of Airport Roadways and Curbsides." 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 2 - Framework for Analysis of Airport Roadways and Curbsides." 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 2 - Framework for Analysis of Airport Roadways and Curbsides." 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 2 - Framework for Analysis of Airport Roadways and Curbsides." 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 2 - Framework for Analysis of Airport Roadways and Curbsides." 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 2 - Framework for Analysis of Airport Roadways and Curbsides." 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 2 - Framework for Analysis of Airport Roadways and Curbsides." 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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3On-airport roadways are a unique class of roadways. Un- familiar drivers mix with significant numbers of professionally driven large vans and buses; entrances and exits at major air- ports operate at near-freeway conditions, while curbside road- ways operate at much slower speeds, as drivers attempt to maneuver into and out of curbside spaces. Double and triple parking and jaywalking frequently occur on curbside roadways despite the visible presence of traffic enforcement officers. Standard highway capacity analysis procedures can address some aspects of these conditions, but not the full spectrum of operating conditions that exist on airport terminal area and curbside roadways. The various users and types of airport roadways and curbsides, and their unique operating character- istics are described in this chapter. Overviews of (1) the hierar- chy of methods for analyzing airport roadway and curbside operations and (2) roadway capacity and level-of-service con- cepts also are presented. Users of Airport Roadways Airport roadways provide access to and from the multi- ple land uses on an airport. These roadways serve vehicles transporting airline passengers and visitors (in this Guide, “visitors” refers to meeters, greeters, and well-wishers accom- panying or greeting airline passengers), employees of the airlines and other airport tenants, air cargo and mail, as well as vehicles used for the delivery of goods and services, main- tenance, to support airport operations or construction, and other purposes. A multitude of vehicle types use airport roadways. They include private vehicles, rental cars, on-demand and pre- reserved taxicabs, prearranged and on-demand limousines or Town Cars, door-to-door vans, courtesy vehicles, charter buses, scheduled buses, and service and delivery vehicles. Each vehicle/user type has its own special characteristics and affects airport roadway operations differently, as described below. 1. Private vehicles. Privately owned and operated vehicles consist of automobiles, vans, pickup trucks, and motor- cycles used to transport airline passengers, visitors, and employees of the airport operator, airlines, and other air- port tenants. Motorists transporting airline passengers in private vehicles may use the curbside areas, parking facili- ties (including cell phone lots), or both. 2. Rental cars. Rental vehicles, including automobiles and vans, used to transport airline passengers or visitors, are rented by passengers or visitors from rental car compa- nies doing business on or near the airport for the duration of the passengers’ or visitors’ trips. Rental car customers may use the curbside areas, rental car ready and return areas, or both. 3. On-demand taxicabs. Taxicabs provide door-to-door service without prior reservations, which is typically exclu- sive (i.e., for a single party) and provided in vehicles capa- ble of transporting five passengers plus their baggage. These vehicles are typically licensed and regulated by a municipal taxicab authority. Typically, on-demand taxi- cabs wait for deplaning passengers at a taxicab stand (or in a taxicab queue) at the curbside area next to the bag- gage claim area. At large airports, taxicabs may wait in a remotely located taxicab holding or staging area until they are dispatched to the curbside taxicab stand in response to customer demand. 4. Pre-reserved taxicabs. Pre-reserved taxicab service is exclusive, door-to-door transportation provided in vehi- cles capable of transporting up to five customers plus their baggage. Rather than being provided on demand, as tra- ditional taxicab service, pre-reserved taxicabs are pro- vided in response to prior reservations made by airline passengers seeking to be picked up by a specific company or driver, including suburban taxicabs not regulated by the municipal taxicab authority. Passengers with special needs, such as those with skis, golf clubs, large amounts of C H A P T E R 2 Framework for Analysis of Airport Roadways and Curbsides

baggage, disabilities, or passengers using a credit card to pay the fare, may request service by specific vehicles or companies. Typically, pre-reserved taxicabs or taxicabs requested specially are not allowed to wait at the curbside taxicab stand, but are assigned curb space at nearby or alternative locations. 5. Prearranged limousines. Prearranged limousine ser- vice is exclusive door-to-door transportation provided in luxury vehicles capable of transporting a single party consisting of up to five customers (or more in stretch limousines) regulated by a local or state agency. Gener- ally, limousine service is only available to customers who have made prior reservations (i.e., prearranged) and are greeted (or picked up) by a driver having a way- bill or other evidence of the reservations. Some airport operators allow limousine drivers to park at the curb- side and wait for customers; others require that the drivers park in a parking lot or other designated zone and accompany their customers from the terminal to the parking area. 6. On-demand limousines or Town Cars. Privately operated on-demand door-to-door transportation is also provided by exclusive luxury vehicles or “Town Cars” capable of transporting up to five passengers and their baggage. These services are similar to on-demand taxicab services, but are provided in luxury vehicles with higher fares than those charged for taxicab services. 7. Door-to-door vans. Door-to-door or shared-ride van services are typically provided in vans capable of trans- porting 8 to 10 passengers and their baggage. The service is available on both an on-demand and prearranged basis. Passengers, who may share the vehicle with other passen- gers, are provided door-to-door service between the air- port and their homes, offices, or other locations, but may encounter several (typically four or fewer) en route stops. Typically, door-to-door vans wait for deplaning passen- gers at the curbside next to the baggage claim area. Similar to taxicabs, vans may be required to wait in hold or stag- ing areas until they are dispatched to the curbside in response to customer demand. 8. Courtesy vehicles. Door-to-door courtesy vehicle service is shared-ride transportation provided by the operators of hotels, motels, rental car companies, parking lot operators (both privately owned and airport operated parking lots), and others solely for their customers. Typically, no fare is charged because the cost of the transportation is consid- ered part of, or incidental to, the primary service being provided. Courtesy vehicle service is provided in shuttle vehicles, including 8- to 12-passenger vans (e.g., those operated by small motels), minibuses, and full-size buses (e.g., those operated by rental car companies at large air- ports). Typically, courtesy vehicles pick up customers at designated curbside areas that have been reserved or allo- cated for their use. 9. Charter buses. Charter bus service (also referred to as tour bus or cruise ship bus service) is door-to-door service pro- vided to a party (or group of passengers) that has made prior reservations or arrangements for the service. Char- ter bus and van service is provided using over-the-road coaches, full-size buses, minibuses, and vans seating more than five passengers. Since charter bus service is sporadi- cally provided at most airports, curb space (or other passenger pickup areas) is either not allocated for char- ter buses or is shared with other transportation modes. Exceptions include airports serving large volumes of char- ter or cruise ship passengers on a regular basis. Typically, charter buses are required to wait in a remotely located hold area until the arrival or assembly of the party being provided the service. 10. Scheduled buses. Scheduled buses provide shared-ride service at established stops along a fixed route and oper- ate on a scheduled basis. Typically, scheduled buses are operated by a public agency and make multiple stops along a designated route, but in some communities express or semi-express service is operated by a private operator or public agency. The location and amount of curb space allocated to scheduled buses depends on the volume of such service and the policy of the airport operator. 11. Service and delivery vehicles. Service vehicles include a wide range of trucks, vans, and semi-trailers, and other delivery vehicles used to transport goods, air cargo and mail, contractors, and refuse to and from the airport. Generally, deliveries are made at designated loading docks or warehouses, not at the terminal curbside. However, the pickup and drop-off locations for airline-operated small package delivery services, which are provided by small vans and light trucks, are at the terminal curbside at some airports. Types of Airport Roadways Although the airport passenger terminal building and sur- rounding area (the terminal area) is the most prominent location on an airport, depending on the size, type, and distri- bution of airport land uses, less than half of all traffic on an air- port may be associated with passengers and visitors proceeding to/from the terminal area; the remaining traffic is generated by nonairline passenger activities, including employees. Regard- less of airport size, the variety of land uses found on an airport requires a network of roadways to provide for inbound and outbound traffic, and the internal circulation of traffic between land uses. The roadway network consists of the types of road- ways depicted on Figure 2-1. 4

Access Roadways For purposes of this Guide, airport access roadways are defined as the roadways linking the regional highway and road- way network with the airport terminal and other areas of the airport that attract large volumes of airline passenger-generated traffic, such as parking and rental car facilities. Access road- ways provide for the free flow of traffic between the regional network and the passenger terminal building or other major public facilities, and typically have a limited number of deci- sion points (i.e., entrances or exits). At large airports, access roadways are often limited-access roadways with both at-grade intersections and grade-separated interchanges. At smaller airports, access roadways often have at-grade intersections that may be signalized, stop-sign controlled, or have round- abouts (yield-sign controlled). Curbside Roadways Curbside roadways are one-way roadways located immedi- ately in front of the terminal buildings where vehicles stop to pick up and drop off airline passengers and their baggage. Curbside roadways typically consist of (1) an inner lane(s) where vehicles stop or stand in a nose-to-tail manner while pas- sengers board and alight, (2) an adjacent maneuvering lane, and (3) one or more through or bypass lanes. Curb space is often allocated or reserved along the inner lane for specific vehicles or classes of vehicles (e.g., taxicabs, shuttle buses, or courtesy vehicles), particularly at the curbside areas serving baggage claim or passenger pickup. As shown on Figure 2-2, depending on the configuration of the adjacent terminal building, curbside roadways may include one, two, or more vertical levels and/or one, two, or more parallel roadways separated by raised medians (often called islands). At airports with dual-level curbsides, the upper level curbside area is at the same level as airline passenger ticketing and check-in facilities inside the terminal and is intended for passenger drop-off. The lower level curbside area is at the same level as the baggage claim area and is reserved for passenger pickup. At airports with multiple terminals where one of the parallel roadways serves as a bypass roadway, cut-through 5 Figure 2-1. Hierarchy of airport roadway classifications.

roadways may be provided to allow vehicles to circulate between the inner and outer parallel roadways (and curb- side roads). Circulation Roadways Circulation roadways generally serve a lower volume of traf- fic and are less direct than the roadways served by access road- ways. Circulation roadways often provide a variety of paths for the movement of vehicles between the terminals, parking, and rental car facilities. Examples include return-to-terminal road- ways that allow motorists to proceed to parking after having dropped off airline passengers (or proceed from parking to the terminals) and allow courtesy or other vehicles to return to the terminal (e.g., after having dropped off enplaning airline pas- sengers and returning to pick up deplaning passengers on a 6 Figure 2-2. Typical airport curbside configuration.

different curbside roadway). Compared to access roadways, circulation roadways typically operate at lower speeds and allow for multiple decision points. The above roadways—access roadways, curbside road- ways, and circulation roadways—are considered “curbside and terminal area” roadways and are the focus of this Guide. Other airport roads include service and access roads, as described below. Service Roads Service roads link the airport access roadways with on- airport hotels, employee parking areas, and employment centers (e.g., aircraft maintenance facilities or hangars), air cargo/air freight buildings and overnight parcel delivery services, loading docks/trash pickup areas, post offices, fixed- base operators (FBOs) or general aviation areas, airport maintenance buildings and garages, military bases, and other nonsecure portions of the airport that generate little airline passenger traffic. The traffic generated by these land uses differs from that gen- erated by the passenger terminal building in several respects. First, the traffic on service roads includes a higher proportion of trucks, semi-trailers, and other heavy vehicles than the traf- fic on curbside and terminal area roadways, which rarely serve trucks or delivery vehicles. Second, most drivers on the service roads (e.g., employees and drivers of cargo vehicles) use these roads frequently and are familiar with the roads and their des- tinations, unlike drivers using the curbside and terminal area roadways. For purposes of operational analyses, the service roads are similar to those found in an industrial park. Typically, they consist of two- to four-lane roads with generous provision for the turning paths of large trucks and semi-trailers and for entering and exiting vehicles, including separate or exclusive turning lanes. Airfield Roads A separate network of roads located within the aircraft operating area or the airfield is used by ground service equip- ment, including vehicles servicing aircraft, towing aircraft, or towing baggage carts and vehicles used for runway mainte- nance or emergency response. Often these vehicles are not licensed to operate on public streets. Only drivers with air- field licenses are permitted to operate vehicles with aero- drome permits in secure or restricted areas. The design and operation of these roads is addressed in guidelines issued by the FAA Series 150 Advisory Circulars The remainder of this Guide addresses curbside and termi- nal area roadways only. Operating Characteristics of Airport Terminal Area Roadways The operating characteristics of airport terminal area road- ways differ from those of other public roads. This section describes the distinguishing operating characteristics of airport terminal area roadways, weaving sections, and curbside areas. What Makes Airport Roadway Operations Unique The main differences between the operating characteristics of airport terminal area access and circulation roadways and nonairport roadways include • A high proportion of unfamiliar motorists. Because most airline passengers fly infrequently (e.g., fewer than four times per year), they (and the drivers who are dropping them off/picking them up) are not familiar with the road- ways at their local airport(s), much less the roadways at their destination airport(s). Unlike commuters, who rarely need to refer to roadway signs, airline passengers rely upon signs (or other visual cues) to guide them into and out of an air- port and to/from their destinations on the airport. Picking up passengers may be particularly challenging for unfamil- iar motorists, who must follow the appropriate signs, be aware of all the traffic and pedestrian activity at the curbside areas, and also be able to identify their party among crowds of other passengers waiting to be picked up. • Large number of complex directional signs. Directional signs on airports often provide more information (i.e., more lines of text) than those on public roadways governed by the Manual of Uniform Traffic Control Devices (published by FHWA) because of the number of terminals, separation of departures and arrivals level roadways, airlines, parking options, and rental car companies that must be provided to motorists (see Figure 2-3). For example, the general policy at U.S. airports is to display the name of every airline serving an airport, even those operating only a few times a week. The signs often include colors, fonts, symbols, and messages not used on other public roadway signs. Because of the number, size, and complexity of these signs, motorists may not see regulatory or warning signs concerning height restrictions, parking rates, security reg- ulations, use restrictions (e.g., authorized vehicles only), and other messages. These signs may result in an overload of information and cause motorists to decelerate while attempting to read the signs. • Stressful conditions. Motorists operating on airport roadways are under more stress than typical motorists. This stress results from the knowledge that minor delays or 7

wrong turns may cause a person to arrive too late to check baggage, claim a pre-reserved seat, or greet an arriving pas- senger, or in an extreme case, miss a flight entirely. Con- gested airport roadways, closely spaced decision points, and complex signs can add to this stress and discomfort. Factors adding to passenger stress at an airport include the need to connect from a car to a plane, from a car to a bus, find a parking place, find a passenger (“Where is Aunt Meg?”), find the correct place to drop off or pick up a pas- senger, locate the taxicab, courtesy vehicle, or city bus stop, and so forth. Passengers realize the importance of making correct decisions in an environment that is more compli- cated and anxiety-filled than a typical roadway situation so that they do not miss their flights or rides. Each action on an airport is part of a chain of events, any one of which can go wrong and disrupt or delay a vacation, business meet- ing, or other important event. • High proportion of large vehicles. More than 10 types of ground transportation services operate on airport road- ways. The characteristics of each service, the needs of the customers using the services, and the operating character- istics of the vehicles used to provide these services must be considered when developing physical and operational plans for airport curbside and terminal area roadways. Courtesy vehicles, door-to-door vans, scheduled buses, and other large vehicles may represent 10% to 20% of the traffic volume on a terminal area roadway. On a typical pub- lic street, less than 10% of the traffic consists of large vehi- cles. Standard Highway Capacity Manual (HCM) capacity calculation procedures reduce the capacity of a public high- way with a high percentage of truck, bus, and other large vehicle traffic to account for the slower acceleration/ deceleration characteristics of these vehicles. However, the use of a capacity adjustment factor may not be necessary on airport terminal area roadways because courtesy vehicles, vans, and buses operating on those road- ways do not interfere with the flow of other traffic to the extent that they do on public highways. On airport termi- nal area roadways, these large vehicles can operate at the range of prevailing speeds typically found on airport road- ways (i.e., 25 miles per hour [mph] to 45 mph) and have sufficient power to accelerate and decelerate at rates that are comparable to those of private vehicles—and do so unless they are transporting standing passengers—because most airport roadways are level or have gentle vertical slopes. Additionally, large vehicles such as courtesy vans or shuttle buses may obstruct motorists’ views of wayfinding signs and may interfere with the operation of passing vehicles as they enter or exit curbside areas. • Mix of experienced and inexperienced drivers. Although most private vehicle drivers use an airport infrequently, 20% to 30% of the vehicles on airport roadways are oper- ated by professional drivers who are thoroughly famil- iar with the on-airport roadways because they use them frequently—perhaps several times each day. This difference contributes to vehicles operating at a range of speeds on the same roadway segment—slow-moving vehicles (e.g., un- familiar drivers of private vehicles attempting to read signs or complete required turns and maneuvers) and faster vehi- 8 Figure 2-3. Complex airport roadway signs. Source: LeighFisher.

cles (e.g., taxicabs and limousines operated by professional drivers familiar with the airport roadways and who may ignore posted speed limits). • Recirculating traffic. Traffic officers often require motorists to exit the terminal area if they are not actively loading or unloading passengers, unable to find an empty curbside space, or waiting for an arriving passenger who is not yet at the curbside. Motorists exiting the curbside area may either wait in a cell phone lot until the passenger arrives (which is encouraged by airport operators) or recirculate around the airport and back to the curbside. Table 2-1 indicates the per- centage of roadway traffic that recirculates past the terminal more than once. These recirculating vehicles contribute to roadway conges- tion and represent unnecessary traffic volumes. Factors con- tributing to recirculating roadway traffic include (1) stricter enforcement procedures required by current security regula- tions, (2) motorists who may not understand the difference between the published flight arrival time and the time when a passenger arrives at the curbside, (3) motorists waiting for passengers whose flights have been delayed, and (4) drivers of commercial vehicles who, in violation of airport regula- tions, are improperly soliciting customers along the curbside roadway. What Makes Airport Roadway Weaving Section Operations Unique Weaving is defined as the crossing of two or more traffic streams traveling in the same direction along a length of highway without the aid of a traffic signal or other control device. A weaving maneuver occurs when vehicles enter a roadway segment from one side and exit the segment on the other while other vehicles do the opposite at the same time. The most common example of weaving occurs on freeways where an on-ramp is followed by an off-ramp a short dis- tance later, and those two ramps are connected by an auxil- iary lane. The weaving movement occurs when vehicles on the freeway move into the auxiliary lane to exit via the off- ramp, while vehicles from the on-ramp move from the aux- iliary lane onto the freeway. The operation of weaving and merging areas on airport roadways differs from the operation on nonairport roadways primarily because these operations occur at slower speeds on airport roadways than they do on freeways and arterial streets. Weaving analyses generally are conducted for freeways and arterial streets on which vehicles operate at higher speeds than those on most airport roadways. At high speeds, drivers require large gaps between successive vehicles in order to merge into, or weave across, a traffic stream. In the 2000 HCM, it was assumed that a free-flow speed of 35 mph on a weaving section represents level of service (LOS) E (i.e., operations at or near a roadway’s capacity—the HCM chapters on weaving and merg- ing were prepared for freeways). Thus, the metrics used in the HCM to establish satisfactory weaving conditions are not suit- able for analysis of airport roadways, which operate at lower speeds than freeways. Chapter 4 of this Guide presents alterna- tive metrics and analysis methods for use on airport roadways. Upon entering an airport, motorists typically encounter a series of exits or turns leading to nonterminal areas (e.g., econ- omy parking, air cargo, general aviation), close-in parking (hourly, daily, or valet) and rental car return (by company), and ticketing/departures vs. baggage claim/arrivals curbside areas. Upon exiting the airport, motorists may encounter a similar series of exits as well as roads leading back to the terminal and alternative regional destinations. Often, the distance between successive decision points is much less than that suggested by highway design standards established for limited access highways because of the relatively short distances available between an airport entrance and the terminal area. Unlike a regional highway where decision points may be separated by a mile or more, successive decision points on an airport may be separated by 500 feet or less. Even though motorists on airport roadways are traveling at speeds (e.g., 35 mph or less) that are slower than those on freeways or arte- rial roadways, the limited distances between decision points compromise the ability of motorists to recognize, read, and react to roadway guide signs, or do not allow adequate time to complete required merging and weaving maneuvers. What Makes Airport Curbside Operations Unique As noted in Chapter 1, curbside roadways consist of the inner curbside lane(s) where vehicles stop or stand typically in a nose-to-tail arrangement while passengers board and alight, an adjacent maneuvering lane that vehicles may occupy while decelerating or accelerating to enter or exit the curbside lane, and one or more “through” or bypass lanes. The operating characteristics of airport terminal curbsides differ significantly from those of most other roadways because of the interactions 9 Table 2-1. Percentage of private vehicles recirculating to the arrivals curbside. Airport Baltimore/Washington International Thurgood Marshall Airport San Francisco International Airport Seattle-Tacoma International Airport Dallas Love Field Reagan Washington National Airport Recirculating (%) 50% 43% 30% 26% 15% Source: Based on data provided by Ricondo & Associates, Inc., June 2009.

between vehicles maneuvering into and out of curbside spaces and vehicles traveling in the through or bypass lanes. The capacity of a curbside roadway is defined both by the number of vehicles that can be accommodated while stopping to pick up or drop off passengers and the number that can be accommodated while traveling past the curbside in the through lanes. The capacity of the through lanes is restricted by vehicles that are double parked (which is often tolerated on airport curbside roadways) or triple parked. These capacity restric- tions can cause traffic delays and the formation of queues that block vehicles trying to maneuver around stopped vehicles or attempting to enter and exit curbside spaces. (Additional infor- mation on the operating characteristics of curbside roadways is presented in Chapter 5.) The length (or capacity) of a curbside area must be in bal- ance with the capacity of the through lanes drivers use to enter and exit the curbside area. For example, a mile-long curbside served by only two lanes (one curbside lane and one through lane) would be imbalanced because, even though the curb length could accommodate a large number of vehicles, traffic flow in the single through lane would be delayed every time a vehicle maneuvers into and out of a curbside space or double parks waiting for an empty space. The reverse imbal- ance would occur with a very short curbside area and multi- ple through lanes. Other operating characteristics of airport curbside road- ways that differ from public roads, as further described in Chapter 5, include the following: • Dwell times. The length of time a vehicle remains stopped at the curbside area is referred to as “dwell time.” Generally, vehicles transporting a large number of passengers and bag- gage require a long dwell time. The number of vehicles that can be accommodated along a given curbside length is determined by the size of the vehicles (i.e., the length of the stall each vehicle occupies, including maneuvering space in front of and behind the vehicle) and the amount of time each vehicle remains at the curbside (i.e., the dwell time). Dwell times at a particular airport are affected by enforce- ment policies (i.e., strict enforcement leads to shorter dwell times) and local driver behavior (e.g., do drivers double park in a way that allows other motorists to easily enter and exit the lane adjacent to the terminal?). Motorists dropping off passengers typically have shorter dwell times than those picking up passengers (unless motorists are prohibited from waiting for the arrival of a deplaning passenger). Thus, since airports generally have equivalent volumes of originating and terminating airline passengers (and associated traffic volumes), the required capacity or length of an arrivals (pickup) curbside area is typically greater than that of the departures (drop-off) curbside area. • Maneuvering traffic and parking preferences. Unlike motorists on city streets, motorists parallel parking at air- ports rarely back into a curbside space. Motorists frequently stop with their vehicles askew to the travel lanes or sidewalk areas rather than maneuvering their vehicles into positions parallel to the curbside. By doing so, they may block or interfere with the flow of traffic in other lanes. Motorists leave space between successive vehicles to assure that they are not blocked and to allow access to the trunk or baggage storage area. Motorists using airport curbside roadways may stop in the second lane even if there is an empty space in the curb- side lane to avoid being blocked in by other motorists and to reduce the walking distances of passengers being dropped off (e.g., stop near a desired door or skycap position) or being picked up (e.g., stop at a point near where the person is standing). Thus, motorists frequently stop in the second lane in front of the door serving the desired airline even though there may be an empty curbside space located down- stream. The propensity to avoid inner lanes and double park reflects local driver behavior or courtesy. • Capacity of adjacent through lanes. Through-lane capacity is reduced by traffic entering and exiting curbside spaces, high proportions of vehicles double and triple parking, the use of the maneuver lanes, and other factors. As such, the capacity analysis procedures presented in the 2000 HCM are not applicable. Chapter 5 of this Guide presents suggested methods for calculating the capacities of curbside lanes and through lanes at airports. • Uneven distribution of demand. Curbside demand is not uniformly distributed during peak periods, reflecting (1) air- line schedules and (2) the uneven distribution of the times passengers arrive at the enplaning curbside prior to their scheduled departures (lead time) or the times passengers arrive at the deplaning curbside after their flights have landed (lag times). Furthermore, stopped vehicles are not uniformly distributed along the length of a curbside area, reflecting motorist preferences for spaces near specific doors and sky- cap positions and their aversion to spaces near columns or without weather protection, if weather-protected spaces are available. An aerial view of a busy terminal curbside area would show vehicles stopped adjacent to the door(s) serving major airlines. When a new terminal is opened, the airline with the largest market share frequently gets the first choice of ticket counter and baggage claim area locations. Often, this airline selects the most prominent location, which gen- erally is the area nearest the entrance to the curbside area. Thus, curbside demand is often heaviest at the entrance to the curbside area, causing double-parked vehicles and congestion in this area, while downstream areas remain unoccupied. 10

• Allocation of space for commercial vehicles and other uses. At most airports, curb space is allocated to commercial vehicles on the pickup curbside area. In the allocation of commercial vehicle curb space, multiple factors must be considered in addition to calculated space requirements, such as customer service, operational needs, airport poli- cies, revenues, and perceived or actual competition among ground transportation services. Curb space may also be allo- cated for disabled parking, police vehicles, airport vehicles, valet parking drop-off/pickup, tow trucks, and other users. • Allocation of traffic on inner and outer curbside areas. At airports having inner and outer curbside areas, one curbside area is generally allocated for private vehicles and the other curbside area(s) is (are) allocated for commercial vehicles. It may be difficult to direct private motorists—especially those unfamiliar with the airport—to multiple curbsides (or sup- plemental curbsides) and, as such, supplemental curbsides are rarely used. Conversely, it is fairly common to direct commercial vehicles to multiple curbside areas. • Crosswalk location, frequency, and controls. Crosswalks provide for the safe movement of pedestrians between the terminal building and center island curbside areas or a park- ing facility located opposite the terminal. The use of cross- walks can be encouraged and jaywalking discouraged by providing numerous crosswalks at convenient (i.e., closely spaced) locations and/or fences or other barriers to pedes- trians along the outer island. However, providing multiple crosswalks adversely affects the flow of through traffic. Motorists are often required to stop at more than one crosswalk because traffic controls at the crosswalks (whether traffic officers or signals) are rarely coordinated in such a way as to allow a continuous flow of through vehicles, such as commonly occurs on an urban street. Multiple crosswalks also reduce the available length of curb space. A single crosswalk has less impact on through traffic and available curb length than multiple, unsignal- ized crosswalks, although multiple crosswalks are more convenient. • Curbside lane widths. At most airports, curbside roadway lane widths are the same as those on public streets (e.g., 10 to 12 feet). Recognizing the tendency of drivers to double park, some airport operators have elected to delineate one double-wide (e.g., 20 to 24 feet) curbside lane rather than two adjacent 10- to 12-foot lanes. (See Figure 2-4.) • Availability of short-duration parking. Curbside demand can be influenced by the availability and price of conve- niently located, short-duration (e.g., hourly) parking. If such parking is readily available and reasonably priced, fewer motorists may choose to use the curbsides. Conversely, the perceived lack or high cost of available short-duration park- ing spaces can discourage motorists from parking and instead lead to increased curbside demand. Similarly, the availability of cell phone or call-and-wait lots can reduce curbside roadway traffic volumes. • Multiterminal airports. Large airports may have multiple terminals, each with separate curbside areas, or continuous curbsides that extend between terminal buildings. Curbside operations at each terminal may differ, reflecting the char- acteristics of the dominant passenger groups and airlines (e.g., international vs. domestic passengers, or legacy vs. low cost carriers). • Recirculating or bypass traffic. At many airports, there is a significant proportion of nonstopping or bypass traffic on the terminal curbsides. This bypass traffic includes (1) recir- culating traffic that, because of police enforcement or other reasons, passes the terminal curbside (particularly the deplaning curbside) more than once, (2) curbside traffic destined for another terminal or adjacent curbside section, which must bypass the curbside in question, and (3) non- curbside traffic traveling past the curbside (e.g., cut-through vehicles, employee vehicles, or airport service or mainte- nance vehicles). • Nonstandard curbside configurations. Although most air- ports have linear curbsides where vehicles stop bumper to bumper or nose to tail, a few airports have nonstandard curbside configurations. – Pull-through private vehicle spaces. As shown on Fig- ure 2-5, the curbside areas at some U.S. airports (e.g., Lambert-St. Louis International, Nashville International, and Little Rock National Airports), as well as many over- seas, have (or had) pull-through spaces arranged at 45-degree angles that allow motorists to pull through, similar to the way they would at a drive-through window. 11 Figure 2-4. Double-wide curbside lane at Washington Dulles International Airport. Source: LeighFisher.

– Angled commercial vehicle spaces. The commercial vehicle curbside areas at the airports serving Atlanta, Newark, and Orlando, among others, have angled spaces that require vehicles to back up to exit. – Driver-side loading. As shown on Figure 2-6, at a few air- ports (e.g., Bush Intercontinental Airport/Houston and Mineta San Jose International Airport), the deplaning curbsides are located on the driver’s side of the vehicle, requiring private vehicle passengers to open the door and enter or exit the vehicle on the side away from the termi- nal building while standing in a traffic lane. Driver-side loading is used at some airports for taxicabs because pas- sengers may enter the cab from either side of the vehicle. – Brief parking zones—pay for curbside use. Some Euro- pean airports do not provide free curb space, but instead provide parking areas adjacent to the terminals that motorists can use for a fee. These areas can be configured parallel to the curbside (see Figure 2-7) or in a traditional parking lot adjacent to the terminal building (see Fig- ure 2-8). In Europe, unattended vehicles are permitted in these zones, but in the United States, current security regulations prohibit unattended vehicles at the terminal curbsides. – Supplemental curbsides. Some airports provide sup- plemental curbsides in or near parking structures or at remotely located sites. Examples of airports with curb- side areas within parking structures include those at the airports serving New York (LaGuardia), St. Louis, and Salt Lake City (see Figure 2-9). 12 Source: LeighFisher. Figure 2-5. Pull-through curbside lanes at Brussels Airport. Figure 2-6. Driver-side loading at Mineta San Jose International Airport. Figure 2-8. Brief parking curbside zone at Munich Airport. Figure 2-7. Pay for curbside use at Paris Charles de Gaulle International Airport. Source: LeighFisher. Source: LeighFisher. Source: LeighFisher.

The analytical procedures described in this Guide are most relevant for airports with traditional curb spaces because of the differing dwell times and through-lane operations that occur with other configurations. Overview of Analytical Framework Hierarchy Subsequent chapters of this Guide present alternative meth- ods for analyzing airport roadways, weaving sections, and curbside areas, recognizing the unique characteristics of these facilities. The alternative analysis methods or hierarchy differ in terms of (1) the level of effort or time needed to conduct the analysis, (2) the expected level of accuracy or reliability of the results, and (3) the necessary level of user skill or experience. The three methods—quick-estimation methods, macroscopic methods, and microsimulation methods—are described in the following paragraphs. Quick-Estimation Methods Quick-estimation methods, as the name suggests, can be used simply and rapidly to produce preliminary analyses of roadway operations (or other facilities). They generally con- sist of look-up tables, simple formulas based on regression analysis of databases, or rules of thumb, and are based on broad assumptions about the characteristics of the facility being analyzed. As such, they provide a first test of the ability of a roadway or other facility to properly accommodate the estimated requirements (existing or future) or the adequacy of a potential improvement measure. Quick-estimation methods are ideal for quickly sizing a facility. The analyst can easily check which of many possible roadway design options is sufficient to serve the forecast demand. These methods, however, are less than satisfactory for estimating the operating performance of a given roadway or for refining a given design. If information on the actual per- formance of a given facility or how to refine a particular design is desired, then macroscopic methods (described below) should be used. Macroscopic Methods Macroscopic methods are used to consider the flows of vehi- cle streams, rather than the flows or operations of individual vehicles. The HCM is an example of a set of macroscopic meth- ods for evaluating roadway operations. As such, these methods approximate the interactions between individual vehicles, the behavior of individual drivers, and detailed characteristics of the roadways (or other facilities). Adjustment factors, typically developed through empirical observations or microsimulation methods, often are used to account for atypical vehicles or driver characteristics, traffic flow constraints, or other opera- tional characteristics. These methods produce results that are considered acceptable, more accurate than quick-estimation methods, and can be used with less training and experience than microsimulation methods. Macroscopic methods can provide reliable estimates of the steady-state performance of a roadway averaged over a given analysis period. They are best for determining the refinements to a proposed design (or existing facility) that would elimi- nate capacity and congestion problems. These methods are less satisfactory for quantifying facility operations under heavy congestion conditions. Macroscopic methods are generally unsatisfactory for com- paring alternative improvements that reduce but do not elim- inate congestion. Under heavily congested conditions (hourly demand exceeding capacity), queuing vehicles from one part of the roadway affect both upstream and downstream opera- tions in a manner that cannot be estimated easily using macro- scopic methods. Macroscopic methods also cannot be used for unusual facility types or situations for which they were not designed. In those situations, microsimulation methods must be used. Microsimulation Methods Microsimulation methods consist of the use of sophisti- cated computer programs to simulate the operation of indi- vidual vehicles on simulated roadway networks. Each vehicle is assigned characteristics, such as a destination, perfor- mance capabilities, and driver behavior. Each roadway net- work is defined using characteristics such as number, length, and width of lanes; operating speeds; traffic controls; and pedestrian activity. As each imaginary vehicle travels through the computerized roadway network, various aspects of its 13 Figure 2-9. Supplemental curbside at Salt Lake City International Airport. Source: LeighFisher.

performance can be recorded based on its interaction with other vehicles and traffic controls. These performance statis- tics can be summarized in many ways, including commonly used performance measures, such as travel time and delays, travel speeds, and queue lengths. Also, some microsimulation models produce a visual display of the simulated roadway operations, which can be helpful when evaluating operations or presenting results. Of the three methods for analyzing airport roadway condi- tions, microsimulation methods are the most complex and require the most effort and skill on the part of the user, but they also produce the most detailed and reliable results. The use of microsimulation methods is suggested when macroscopic methods do not yield reasonable results, do not provide suffi- cient detail, or when the conditions being analyzed are outside the ranges addressed by macroscopic methods. Additional information regarding the application of these three analysis methods is presented in subsequent chapters of this Guide. Overview of Capacity and Level-of-Service Concepts The concepts of capacity and level of service, as presented in the 2000 HCM, are fundamental to analyses of roadway and other transportation facilities and well understood by traffic engineers and transportation planning professionals. This sec- tion is intended to provide an overview of these concepts for users not familiar with the 2000 HCM. Capacity Concept The capacity of a rectangle or a box can be defined easily by its size (i.e., its area or volume) because the maximum amount the object can accommodate is fixed. This is not true with objects that serve as “processors,” such as roadways, ticket counters, or runways. The capacity of a roadway, for example, depends not only on its size (e.g., the number of lanes and other geometric design aspects), but also on the characteristics of the vehicles using the roadway (e.g., their size, performance, spacing, speed, and many other operating characteristics). If all the vehicles on a roadway were identical in size, distance apart, speed, driver characteristics, and other characteristics, then the capacity of the roadway (number of vehicles travers- ing a point or section during a unit of time) would be expected to be substantially higher than the capacity of the same road- way if it were serving a mix of vehicle sizes, speeds, and driver characteristics. Accordingly, the capacity of a roadway—even roadways with the same number of lanes—varies based both on the char- acteristics of the roadway (e.g., lane and shoulder widths, ver- tical grades, intersection and driveway spacing, and traffic control types) and the characteristics of the vehicles and driv- ers using the roadway (e.g., the proportion of trucks or heavy vehicles, daily and hourly variations in use, familiarity of the typical drivers with the roadway). With knowledge of the char- acteristics of a roadway section and the vehicles (and drivers) using the roadway, it is possible to calculate its capacity—the “maximum hourly rate” of vehicles flowing past a point. However, it is not possible or desirable for a roadway to operate at its capacity for sustained periods, because any minor disruption will cause congestion, which results in delays or lengthy queues and undesirable levels of safety and driver com- fort. Thus, roadway capacity, while stated in terms of “base” vehicles (e.g., passenger car equivalents) per hour, is sometimes computed for only the peak 15-minute flow rate within that hour. In addition, roadway operations are characterized in terms of level of service and “service flow rate”—the maximum flow rate that can be accommodated while maintaining a des- ignated level of service. Similar to capacity (maximum hourly vehicle flow rates), service flow rates vary according to the characteristics of a roadway section and the vehicles using the roadway. Level-of-Service Concept Level of service is a qualitative measure of roadway (or other transportation facility) operations. Six levels of service are defined in the 2000 HCM, with LOS A representing the highest (or best) level of service and LOS F representing the lowest (or worst) level of service. The 2000 HCM defines level of service as follows: . . . a quality measure describing operational conditions within a traffic stream, generally in terms of such service measures as speed and travel time, freedom to maneuver, traffic interrup- tions, and comfort and convenience. Levels of service are defined in terms of parameters that can be perceived by the users of a transportation facility and that can be measured and predicted. On roadways, each level of service corresponds to a specific maximum flow rate (i.e., the upper limit of the performance measure threshold (or flow rate)) for that level of service. The parameters or measures of effectiveness defining each level of service are (1) the density of the traffic flow (passenger cars per mile per travel lane) for a freeway or other unsignalized multilane roadway and (2) delay (seconds per vehicle) for signalized and unsignalized intersections. Commonly Used Level-of-Service Definitions for Airport Terminal Area Roadways As noted, the 2000 HCM defines six levels of service, as pre- sented below. (These definitions were taken from the 2000 14

HCM, but have been modified slightly for the benefit of airport planners and others not familiar with the HCM.) LOS A represents operations where free-flow speeds prevail. The ability of each driver to maneuver within the traffic stream, change lanes, merge, or weave is almost completely unimpeded by other vehicles because of low traffic densities. The effects of transient blockages or incidents (e.g., an accident, vehicle break- down, or other event that impedes the flow of traffic) are easily absorbed at this level of service. LOS B represents conditions in which free-flow speeds are maintained. The ability of each driver to maneuver within the traffic stream, change lanes, or weave is only slightly restricted by the presence of other vehicles. The general physical and psy- chological comfort of drivers is still high. The effects of minor incidents and point breakdowns (e.g., a breakdown in traffic flow where traffic enters, leaves, or crosses a roadway) are still easily absorbed. LOS C represents traffic flow with speeds at or near the free- flow speeds of the roadway. Freedom to maneuver within the traffic stream is noticeably restricted (by the presence of other vehicles) and lane changes may require more care and vigilance on the part of the driver because of high traffic densities. Minor blockages or incidents may still be absorbed, but the local dete- rioration in service will be substantial. Queues may be expected to form behind any significant blockage. On airport roadways, LOS C is generally considered to be the minimum “acceptable” level of service because of the lack of alternative travel paths and the significant negative consequences of travel delays. LOS D represents the level at which speeds begin to decline slightly with increasing flows, and density (on freeways and other roadways with uninterrupted flows) begins to increase somewhat more quickly. Freedom to maneuver within the traffic stream is more noticeably limited (because of the lack of gaps between successive vehicles), and the driver experiences reduced physical and psychological comfort. Even minor blockages or incidents can be expected to quickly create queues because the traffic stream has little space to absorb disruptions. LOS E represents operations at or near capacity. Opera- tions at this level are volatile because there are virtually no usable gaps in the traffic stream. Vehicles are closely spaced, leaving little room to maneuver (or allow for lane changes or weaving) within the traffic stream. Any disruption of the traf- fic stream, such as vehicles entering from a ramp or a vehicle changing lanes, can disrupt upstream traffic flows. At capac- ity, the traffic stream has no ability to absorb even the most minor disruptions, and any incident can be expected to pro- duce a serious breakdown with extensive queuing. Maneu- verability within the traffic stream is extremely limited and the level of physical and psychological comfort afforded the driver is poor. LOS F represents breakdowns in vehicular flow. Such con- ditions generally exist within queues forming behind bottle- neck points. Bottlenecks occur as a result of (1) traffic accidents or incidents, (2) typical traffic congestion areas, such as lane drops, weaving segments, or merges, (3) parking maneu- vers, or (4) traffic conditions when the projected hourly flow exceeds the estimated capacity of the roadway segment. Acceptable Levels of Service for Terminal Area Roadways As noted, levels of service are typically used to determine if a roadway can properly accommodate existing or future traf- fic operations or compare alternative improvement options. On regional freeways and arterials and in densely developed urban areas, LOS D is often considered acceptable because motorists traveling on regional roadway networks can select alternative travel paths should their preferred path be con- gested. However, on airport roadways, where only a single path is available (and the cost of delay to the traveler is great), LOS C is typically considered to be the minimum acceptable level of service because of the lack of alternative travel paths and the significant negative consequences resulting from travel delays (e.g., passengers missing their flights). 15

Next: Chapter 3 - Estimating Airport Roadway Traffic Volumes »
Airport Curbside and Terminal Area Roadway Operations Get This Book
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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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