CHAPTER 6

Improving Airport Curbside and Terminal Area Roadway Operations

This chapter presents examples of commonly occurring airport curbside and roadway operational problems and potential improvement measures.

Analyses and evaluations of airport curbside and terminal area roadways generally involve the following steps:

1. Identify the problem(s). Problem identification includes determining the causes of existing congestion, delays, imbalances in demand, and/or whether the existing (or proposed) roadway network can accommodate anticipated future requirements.
2. Document goals and objectives. Documenting the relevant goals and objectives of airport management (and other stakeholders) with respect to roadway operations is a key step in the analysis and evaluation process. The relevant objectives may include such broad categories as the following:
   • Provide safe and secure operations for airport users.
   • Provide desired levels of customer service for airline passengers, visitors, employees, and other airport users.
   • Accommodate existing and future requirements.
   • Accommodate regional mobility needs/encourage the use of public transportation.
   • Support local, regional, and/or state air quality goals.
   • Support the airport’s ability to maintain or enhance airfield capacity by ensuring that changes to roadways and curbsides do not negatively affect airfield operations or capacities.
   • Maintain and enhance the net revenues generated by the airport.
   • Ensure accessibility for those with disabilities.

   Detailed descriptions and definitions of goals will allow the development of airport-specific objectives that can be used to compare and evaluate alternative improvement measures.

3. Identify and develop potential improvements. The potential improvement measures described in this chapter can serve as a starting point for improvements that address commonly occurring airport curbside and terminal area roadway operations. The following sections present commonly occurring problems and potential improvement measures for terminal area roadways and curbsides, respectively.
4. Evaluate the potential improvements. The alternative analytical methods, described in previous chapters, can be used to quantify the changes expected to result from the potential improvements, assess their advantages and disadvantages, and identify the preferred improvement(s).
5. Reach consensus on the preferred improvement. A key step in the implementation process is to build consensus supporting the selection and implementation of the preferred alternative. An evaluation process that quantifies the extent to which the potential improvement would support the stated goals and objectives of airport management (and other stakeholders) provides a foundation for achieving consensus.

6. Implement the preferred solution. This step could involve design and construction activities, operational improvements, or changes in airport management policies.

6.1 Typical Terminal Area Roadway Problems

Operational and physical problems can adversely affect the ability of terminal area roadways to accommodate traffic efficiently and safely. In this section, 10 types of deficiencies that may occur in an airport environment are identified. These deficiencies can typically result in queues or delays; many airport roadways exhibit one or more of the deficiencies described below. Possible strategies to address these problems are presented in Chapter 7.

6.1.1 Insufficient Roadway Capacity

A roadway has insufficient capacity if, during the analysis period, the roadway operates at “under capacity” or worse (see Chapters 4 and 5 for an explanation of sufficiency categories). “Under capacity” refers to congested roadways and is an unacceptable basis for planning airport roadways. Specific implications of insufficient roadway capacity include (1) congested roadway sections with queues extending to upstream roadways, (2) motorists experiencing frequent congestion and significant delays, and (3) a generally unsatisfactory airport experience.

6.1.2 Insufficient Merging Capacity

Insufficient merging capacity results when a roadway does not provide sufficient capacity at points where two or more streams of traffic combine into a single stream. This deficiency results in roadway delays, congestion, and traffic queues extending back from the merge point. Merge segment capacity is determined by (1) the volume of entering traffic, (2) the operating speeds, and (3) the number of lanes upstream and downstream.

6.1.3 Inadequate Weaving Distance

Inadequate weaving distance results when a roadway does not provide sufficient length or travel lanes to accommodate the traffic volumes at the point where two or more streams of traffic traveling in the same direction cross or merge, causing vehicles to decelerate (or stop) while waiting for adequate gaps in the traffic stream. This deficiency results in (1) vehicle delays and queues, (2) higher accident rates, and (3) slower speeds and flow rates. Factors influencing required weaving distances are operating speeds, traffic volumes (merging, weaving, and flowing through the segment), and the number of lanes that vehicles must cross to complete the desired maneuver.

6.1.4 Lane Imbalance

Lane imbalance results when a roadway segment, before a diverge or after a merge, contains two (or more) fewer lanes than the combined total number of lanes entering or exiting the segment. For example, at a point where two three-lane roadways merge, the downstream segment must consist of at least five lanes, or a lane imbalance will result. At a point where a roadway diverges into two two-lane roadways, the upstream segment (prior to the diverge) must consist of at least three lanes. A lane imbalance can cause (1) increased delays, (2) sudden diverge or weave maneuvers, (3) increases in the required roadway weaving distances (e.g., the number of lanes to be crossed), and (4) higher accident rates. Proper lane balance helps reduce or avoid forced merges, weaves, and sudden maneuvers and is typically accomplished by providing a lane that allows motorists access to both exit routes (e.g., an “either-or” lane) or by extending a lane downstream

past the merge/diverge point and then dropping the lane using design guidelines appropriate for the roadway speed (e.g., taper distances).

6.1.5 Directional Information Overload

Directional or wayfinding information overload occurs when more information (or decisions) is presented to a motorist than the motorist can read, comprehend, and react to in the available time (and distance). This overload causes drivers to weave suddenly, miss exits, make sudden or erroneous movements, or, in extreme cases, stop in the roadway (or on the shoulder) to read the signage.

It is desirable to avoid presenting more than two decisions or more than four lines of text on each directional sign. If more than four lines of text must be used on one sign at an airport, it is necessary to prioritize the information and avoid using unfamiliar or inconsistent terms.

6.1.6 Insufficient Decision-Making Distance

Insufficient decision-making distance is defined as an insufficient distance (or time) for motorists to read, comprehend, and react to information regarding a decision that must be made. This situation causes drivers to weave suddenly, miss exits, make wrong turns, or, in extreme cases, stop in the roadway to read the message or back up to the decision point. Factors contributing to providing the necessary decision-making distance include (1) travel speed, (2) message content, (3) visibility of the decision point, and (4) visibility of the directional signage.

6.1.7 Insufficient Queuing Space

Queuing space represents the area required to accommodate vehicles stopped at an entrance (or exit) to a parking lot or other facility, traffic signal or turn lane, or vehicle inspection area so that vehicles in the queue do not interfere with traffic flow on the adjacent roadway or travel lanes. For example, a parking facility entrance should have sufficient space to accommodate vehicles queuing at the ticket-issuing machines without having the queue extend onto the adjacent roadway.

6.1.8 Unexpected Lane Drops/Inadequate Taper Lengths

Unexpected lane drops and inadequate taper lengths (the distance required to introduce a new lane or drop an existing lane) result when a through lane unexpectedly ends and motorists are required to unexpectedly merge quickly into an adjacent lane. Required taper lengths, which vary according to roadway operating speeds, are intended to allow sufficient distance for lane channelization and vehicle merging. Unexpected lane drops reduce roadway capacity and travel speeds, as motorists who become “trapped” in a lane are required to merge quickly (interfering with the flow of other vehicles in adjacent lanes).

6.1.9 Unexpected Transition from High-Speed to Low-Speed Roadway Environment

Some motorists do not realize they need to slow down as they exit from a regional roadway (which may operate at more than 55 mph) and approach a terminal area roadway (which may operate at less than 30 mph) until they encounter a sharp curve at the entrance to the terminal or vehicles stopped in the roadway. This situation is particularly true at airports where a limited-access highway, designed to freeway standards and capable of accommodating freeway speeds, connects the regional roadway network with the terminal area roadways (see Figure 6-1).

Motorists may be provided few visual clues that the driving environment is changing and requires them to decelerate. In addition, speed limit signs may get lost among the many other signs and distractions associated with roadways approaching an airport terminal.

This transition is compounded by the reduction in roadway capacity that accompanies the speed reduction: a three-lane access roadway operating at 55 mph (or more) has more capacity than a three-lane curbside roadway operating at 30 mph (or less). If the traffic volume on the access roadway is the same as that on the curbside roadway, it is necessary to provide additional travel lanes on the curbside roadway to compensate for the reduction in travel speed. Often, the volumes are not constant, as some traffic exits for non-terminal area destinations, such as parking and rental car facilities.

6.1.10 Missing Movements

Missing movements are defined as a desired travel path or traffic movement that is not provided on an airport roadway network. If a movement is missing, motorists may need to exit and re-enter the airport or travel extra distance. For example, at most major airports, motorists can proceed directly (1) from the enplaning curbside to short-duration parking and (2) from short-duration parking to the deplaning curbside without leaving the terminal area. The absence of roadway segments providing these direct movements increases traffic demand on the return-to-terminal roadways and vehicle miles of travel.

6.2 Typical Curbside Roadway Problems

Operational and physical problems can adversely affect the ability of airport curbside roadways to accommodate traffic safely and efficiently. Typical problems include those listed below. Possible strategies to address these problems are presented in Chapter 7.

6.2.1 Insufficient Curbside Roadway Capacity

Insufficient curbside roadway capacity exists when curbside requirements (lengths) are greater than 1.3 times the usable curbside length and/or the through lanes on a curbside roadway operate at LOS C or worse. When curbside demand exceeds available capacity, motorists experience

significant delays and queues, as evidenced by high levels of double- and triple-parking throughout the entire curbside, which, in turn, reduces the capacity and travel speeds of the curbside roadway through lanes. As noted previously, curbside roadways must provide both adequate curbside length (stopping space) as well as adequate throughput capacities. Any deficiencies in one area will adversely affect the other. Factors that contribute to a lack of curbside roadway capacity are described in the following paragraphs.

6.2.2 Imbalances in Demand

Imbalances in curbside demand occur when the total length of curbside space available is sufficient to accommodate curbside demand, but most of the demand occurs at and overloads the capacity of one segment of the total curbside area. For example, if the airline(s) on one concourse serves most of the peak-hour airline passenger activity, then curbside traffic will be concentrated at the doors leading to the portions of the terminal building occupied by this airline(s), leaving the remainder of the curbside areas empty or underutilized. It is generally not feasible to relocate the assigned airline ticket counter or baggage claim area locations solely to balance curbside demand.

6.2.3 Insufficient Number of Travel Lanes

A curbside roadway that does not provide sufficient capacity to accommodate existing or future requirements at LOS C or better typically has an insufficient number of travel lanes. Generally, curbside roadways with four lanes or more provide sufficient capacity because two travel lanes remain available even when double-parking occurs. Congestion and delays may occur frequently on curbside roadways having three lanes or fewer as any double-parking severely restricts through traffic. Similar restrictions also occur when vehicles are allowed to stop on the inner and outer lanes of a four-lane curbside, leaving only the two center lanes for through traffic.

6.2.4 Pedestrian Crosswalks and Pedestrian Activity

Pedestrians crossing a curbside roadway restrict the volumes of through traffic that can be accommodated. Delays caused by crosswalks are related to (1) the volume of pedestrians walking across a curbside roadway, (2) the proportion of time that pedestrians occupy a crosswalk (properly or improperly), and (3) the number of crosswalks located at curbside. Traffic flows and safety can also be adversely affected by pedestrians stepping into the roadway to avoid columns or other obstacles, hail vehicles, or board/alight from a vehicle stopped in a through lane.

6.2.5 Driveways Serving Adjacent Land Uses

Driveways serving adjacent land uses (e.g., parking lots or rental car ready/return areas) may impede the flow of curbside traffic when vehicles in the lane farthest from the terminal decelerate (or accelerate) as they enter (or exit) the driveways serving the adjacent land uses. Vehicle queues formed at the entrances to these land uses may extend back onto the curbside roadways.

6.2.6 Insufficient Curb Length

Insufficient curb lengths result from curbside demand that is greater than 1.3 times the usable curbside length, which also occurs when there is significant double-parking.

6.2.7 Inefficient Allocation of Curb Space

Inefficient allocation of curb space results where the total available space is adequate to accommodate demand, but the available space has been divided into (or allocated among) many

categories of ground transportation services such that some categories are allocated more curb space than required while others are not allocated enough. This situation may occur when curb space is allocated to vehicles that rarely serve the airport (e.g., charter buses), demands have changed as a result of the introduction of new services, or the space has been broken into small segments that do not correspond to the operational or maneuverability needs of the assigned class of ground transportation service.

Similarly, inefficient allocation of curb space results when the amount of curb associated with a specific airline does not match the relative share of passenger traffic served by that airline.

6.2.8 Unusable Curbside Roadway Geometry

Unusable curbside roadway geometries exist when vehicles cannot stop to load or unload passengers because of the curved alignment of the roadway, narrow sidewalks, or other physical obstructions. Many terminals have curved curbside roadways, but generally, the radii of these roads are very large and motorists do not perceive that they have stopped along a curvilinear section. However, some curbside roadways have small radii or tight curves that hinder a motorist’s ability to park parallel to the sidewalk or to enter or exit this space. Motorists may be unable to park adjacent to curbsides having narrow sidewalks (e.g., the ends of island curbside areas) or columns (or other obstacles) adjacent to the roadways. Large bollards, which are sometimes placed on terminal building sidewalks to protect motorists and the adjacent terminal, may interfere with the ability of motorists to open/close their doors or enter/exit their vehicles.

Narrow sidewalks may also force pedestrians to step into the roadway (with their baggage) to bypass columns, queues of passengers formed at skycap positions or benches, or other obstacles.

6.2.9 Excessive Dwell Times

Excessive dwell times result when vehicles (either private or commercial vehicles) are allowed to remain at the curbside when not actively loading or unloading passengers. In the case of some commercial vehicle providers, excessive dwell times are permitted by airport rules and regulations. Excessive dwell times may reflect insufficient police presence or visibility, or permissive airport policies, and may occur even if the dwell times of most vehicles are within reasonable limits, and fewer than 10% of vehicles remain at the curbside for excessive periods.