SUMMARY

Airport Curbside and Terminal Area Roadway Operations: New Analysis and Strategies, Second Edition

ACRP Research Report 266: Airport Curbside and Terminal Area Roadway Operations: New Analysis and Strategies, Second Edition (the Guide) is intended to assist airport operators, planners, consultants, and individuals tasked with analyzing airport terminal area roadway and curbside operations and to select strategies to mitigate congestion. The Guide, which is an update of ACRP Report 40: Airport Curbside and Terminal Area Roadway Operations, presents guidelines for estimating airport roadway requirements and capacities, recommended performance measures, valid and useful analytical methods, and innovative strategies to reduce traffic demands and mitigate congestion on terminal area and curbside roadway operations.

Operating Characteristics of Airport Roadways

Airport access and circulation roadways, curbside roadways, and service roads are used by a wide variety of vehicles. Vehicles using airport roadways include private vehicles, rental cars, commercial ground transportation vehicles [e.g., taxicabs, transportation network company (TNC) vehicles, limousines or town cars, shared-ride vehicles, courtesy vehicles, and charter and scheduled buses and vans] and service and delivery vehicles, with autonomous vehicles (AVs) expected in the future.

The operating characteristics of airport terminal area roadways differ from those of non-airport roadways because of the high proportion of motorists who are unfamiliar with the airport (as well as the presence of many professional drivers who use the airport frequently). The relatively complex wayfinding, closely spaced decision points, and high proportion of large vehicles add significant stress for a motorist. The operation of weaving and merging areas on airport roadways differs from the operation of these areas on non-airport roadways because these operations occur at slower speeds on airport roadways than they do on freeways and arterial streets.

The operating characteristics of airport terminal curbsides differ significantly from those of most other roadways because of the interactions between vehicles maneuvering into and out of curbside spaces and vehicles traveling in the through or bypass lanes. Compared to vehicles parked on city streets, vehicles remain stopped at the curbside for less time, occupy longer spaces to ensure they can easily exit, frequently double-park or park in an orientation not parallel to the curb, and tend to stop near specific doors. Curbside and terminal area roadway traffic peaking is influenced by airline schedules and the length of time passengers arrive prior to their scheduled departure and leave after their flight has landed. Curbside spaces are frequently reserved for specific uses such as commercial ground transportation vehicles. See Chapter 2 of the Guide for further details about the unique operating characteristics of airport terminal area and curbside roadways.

Estimating Airport Roadway Requirements

Estimates of traffic volumes or requirements for terminal area and curbside roadways can be prepared using the traditional four-step approach, commonly used by transportation planners, or the growth factor method. The four-step process yields separate estimates of the traffic volumes generated by airline passengers, visitors, employees, air cargo handlers, and other major airport land uses. However, this method requires extensive input data describing the characteristics of each of these traffic generators. The growth factor method yields acceptable, but less precise, results while requiring much less input data. However, this simpler method is less sensitive to changes in future conditions or travel patterns. Both methods rely upon observations of existing vehicular activity—traffic volumes, vehicle mix, dwell times, and other data that can be gathered using traffic recording devices, video cameras, Bluetooth sensors, data from connected vehicles, vehicle detectors, and other sources.

Estimates prepared using the traditional four-step approach begin with trip generation (the first step). Estimates of trip generation require data on the (1) number of originating and terminating airline passengers (existing and forecast) and their trip purposes, places of residence, choice of travel modes, circulation patterns, and peaking characteristics; (2) the number of persons employed by the airport, airlines, and other tenants (existing and forecast) and their work schedules, choice of travel modes, and circulation patterns; (3) trips generated by trucks transporting air cargo and persons working at air cargo facilities; and (4) traffic generated by service and delivery vehicles bringing goods and materials to/from the terminals, airport operations and maintenance vehicles, and other sources. The second step (trip distribution) yields an estimate of the proportion of airport-generated traffic using each airport access point and the regional paths these vehicles follow. The third step (trip assignment) results in estimates of the airport-generated traffic volumes on each segment of the airport roadway network, by time of day and type of vehicle. The fourth step compares the estimated traffic volume (airport plus non-airport) on each roadway segment with the capacity of the segment.

Estimates prepared using the growth factor method can apply the ratio between the existing and forecast annual (or peak month or peak hour, as available) airline passenger volumes (originating plus terminating passengers) to the traffic volumes on each roadway segment. The growth factor method can further potentially adjust these volumes to reflect anticipated changes in vehicle mix (resulting from the introduction of transit service or use of AVs, for example) or circulation patterns (resulting from regional transportation improvements or expected congestion).

Chapter 3 provides further detail on estimating airport roadway traffic requirements.

Analyzing Airport Terminal Area Roadway Operations

Airport roadways, weaving sections, and curbside areas can be analyzed using

• Microsimulation, a method that uses sophisticated computer programs to simulate the operation of individual vehicles on simulated roadway networks. Each vehicle and roadway network segment is assigned characteristics reflecting performance capabilities, driver behavior, number of lanes, operating speeds, and pedestrian activity. As each simulated vehicle travels through the computerized network, its performance can be recorded based on its interaction with other vehicles and traffic controls. Of the three methods listed, microsimulation is the most complex and requires the most effort and a specialized set of skills on the part of the user; however, this method provides the most detailed and reliable results. Chapter 4 presents guidelines on the use of microsimulation on airport roadways.

• Macroscopic methods, which consider the flow of vehicle streams rather than the operations of individual vehicles. These methods approximate the interactions between individual vehicles, the behavior of individual drivers, and detailed characteristics of the roadways (or other facilities). Adjustment factors are used to account for atypical vehicles or driver characteristics, traffic flow constraints, or other operational characteristics. These methods produce results that are considered acceptable and more accurate than quick-estimation methods, and macroscopic methods can be used with less effort and training than microsimulation methods. Macroscopic methods are best for determining the refinements to a proposed design (or existing facility) that would eliminate capacity and congestion problems but are less satisfactory for evaluating operations under heavy congestion conditions or on atypical configurations. Chapter 4 reviews macroscopic methods for analyzing airport roadway weaving areas.
• Quick-estimation methods, which can be used to produce preliminary analyses of roadway operations (or other facilities) simply and rapidly. They generally consist of look-up tables, simple formulas using regression analysis of databases, or principles based on experience or practice and are built on broad-based assumptions about the characteristics of the facility being analyzed. Quick-estimation methods are ideal for quickly sizing a roadway or other facility and providing a first test of the facility’s ability to properly accommodate the estimated requirements (existing or future) or the adequacy of a potential improvement measure.

Table 4-1 of the Guide presents the maximum service flow rate and adjusted flow rates for multilane airport roadways with uninterrupted flows. Chapter 4 describes the assumptions used to prepare this table, limitations to its use, and its application. Methods for analyzing signalized intersections and airport roadway weaving sections are also described.

Estimating Roadway Capacities

Roadway capacities are a function of the roadway characteristics and the vehicles and drivers using the roadway. Knowing the characteristics 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. It is not possible or desirable for a roadway to operate at its capacity for sustained periods, as any minor disruption will cause congestion and undesirable levels of safety and driver comfort. Also, demand is rarely sustained at a constant level over an hour.

Roadway operations are characterized in terms of quality-of-service measures and service flow rates—the maximum flow rates that can be accommodated while maintaining a desired quality of service. Quality of service reflects how travelers perceive the performance of roadways and other facilities. While quality of service is often stratified quantitatively into levels of service indicated using the acronym “LOS” (e.g., LOS A to LOS F), the concept is broader and includes system-oriented metrics such as the sufficiency of the roadway to provide adequate capacity.

On airport roadways, a sufficiency of “under capacity” is typically considered to be the minimum “acceptable” level of performance because of the lack of alternative travel paths, the significant negative consequences resulting from travel delays (e.g., passengers missing their flights), and the ability to accommodate higher volumes during short periods and unusually busy days (such as during holidays) without reaching failure. In comparison, on regional freeways and arterials and in densely developed urban areas, a sufficiency of “near capacity” is often considered “acceptable” because motorists traveling on these roads can select alternative travel paths if desired. Chapter 4 presents further details on quality-of-service and sufficiency metrics.

Evaluating Airport Curbside Operations

Evaluations of airport curbside roadway operations require analyses of both the curbside lanes (where motorists pick up or drop off passengers) and the adjacent through lanes. The recommended performance measure for airport curbside roadways is curbside utilization—the ability of a roadway to accommodate vehicles loading or unloading at the curbside during the design hour that indicates a curbside roadway’s level of service. LOS C (illustrated in Figure 5-1 and presented in Table 5-2) is the suggested planning target.

Curbside roadway traffic volumes can be estimated using the same methods as those used for estimating airport terminal area roadway traffic, allowing for separate estimates of through traffic, vehicles dropping off and picking up passengers (by type of vehicle), vehicle dwell times, and pedestrian crossings.

Chapter 5 presents procedures for calculating curbside roadway requirements and factors influencing the requirements. It also describes the use of the Quick Analysis Tool for Airport Roadways (QATAR) for analysis of airport curbside roadway operations and testing how variations in input assumptions affect level of service. Appendix C provides an overview of the curbside analysis methodology in QATAR. QATAR and a user guide for QATAR are available on the National Academies Press website (nap.nationalacademies.org) by searching on ACRP Research Report 266: Airport Curbside and Terminal Area Roadway Operations: New Analysis and Strategies, Second Edition.

Improving Airport Terminal Area and Curbside Roadway Operations

Roadway operations can be adversely impacted by numerous deficiencies, including insufficient roadway length or merging capacity, lane imbalances, wayfinding challenges, insufficient decision-making distances and queuing space, insufficient curbside capacity (i.e., insufficient curb length or travel lanes), unusable curb space, and excessive dwell times. These deficiencies are detailed in Chapter 6.

Chapter 7 presents innovative strategies to improve airport terminal area and curbside roadway operations. These strategies are grouped into three primary categories and four complementary categories (see Figure S-1). The three primary categories are

1. Enforcement strategies, which underpin all other strategies. Without effective enforcement, it is difficult to implement other strategies efficiently and effectively. Enforcement strategies include the appropriate use of enforcement officers, crosswalk controls, regulatory signs, and other strategies.
2. Traffic demand management strategies, which include promoting the use of alternative passenger drop-off and pickup locations, promoting transit use, and charging motorists fees for curbside use.
3. Congestion management strategies, which are intended to improve curbside capacities and traffic flows, improve roadway operations, and control traffic flows.

Four strategy categories complement the three primary strategy categories:

1. Customer service strategies include providing customers with comfortable waiting areas and transit information and having staff available to help at drop-off and pickup areas.
2. Sustainability strategies, which reduce carbon emissions by encouraging the use of long-duration parking rather than drop-off and pickup alternatives and promoting the use of electric vehicles.

3. Accommodating TNCs, which includes operational measures that can be implemented by the TNCs (use of geofences, pooling, and dispatching procedures) and by the airport (providing subzones to help customers find their driver and alternative/remote boarding areas).
4. Accommodating AVs, which includes separating AVs from non-AVs and updating airport regulations and infrastructure in anticipation of the widespread adoption of AVs.

Furthermore, numerous supporting technologies are available to enhance these primary and complementary strategies. These supporting technologies can monitor traffic volumes and locations (by type of vehicle or individual vehicle), automatically dispatch taxicabs and other on-demand services, support curbside enforcement by directing officers to vehicles needing attention, guide motorists by displaying changeable directional or parking information, and provide other capabilities.