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60 Figure 6-1. Insufficient queuing space at parking entry at Tulsa International Airport. roadway operating speeds, are intended to allow sufficient network. If a movement is missing, motorists may need to exit distance for lane channelization and vehicle merging. Un- and re-enter the airport or travel extra distance. For example, expected lane drops reduce roadway capacity and travel speeds, at most major airports, motorists can proceed directly from the as motorists who become "trapped" in a lane are required to enplaning curbside to short-duration parking and from short- merge quickly (interfering with the flow of other vehicles in duration parking to the deplaning curbside without leaving adjacent lanes). the terminal area. The absence of roadway segments provid- ing these direct movements increases traffic demand on the Unexpected Transition from High-Speed return-to-terminal roadways and vehicle miles of travel. to Low-Speed Roadway Environment Potential Terminal Area Roadway Some motorists do not realize they need to slow down as Improvement Measures they exit from a regional roadway (which may operate at more than 55 mph) and approach a terminal area roadway (which Potential improvements to terminal area roadway opera- may operate at less than 30 mph) until they encounter a sharp tions are presented in the following categories: curve at the entrance to the terminal or vehicles stopped in the roadway. This situation is particularly true at airports · Physical improvements, where a limited access highway, designed to freeway stan- · Operational measures, and dards and capable of accommodating freeway speeds, connects · Airport policies. the regional roadway network with the terminal area roadways (see Figure 6-2). Motorists may be provided few visual clues that the driving environment is changing and requires them to decelerate. Additionally, 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 reduction in speed: a three-lane access roadway operating at 55 mph (or more) has more capac- ity 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 addi- tional travel lanes on the curbside roadway to compensate for the reduction in travel speed. Often, the volumes are not con- stant, as some traffic exits for non-terminal area destinations, such as parking and rental car facilities. Missing Movements Figure 6-2. Transition from high-speed to low-speed Missing movements are defined as a desired travel path or airport roadways at Baltimore/Washington traffic movement that is not provided on an airport roadway International Thurgood Marshall Airport.
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61 A general planning principle for the design and operation listed in Appendix B, including those published by AASHTO, of airport roadways is to separate traffic generated by airline provide additional information on this topic. passengers and visitors from that generated by employees, · Adding exclusive left- or right-turn lanes. The capacity of air cargo, and services or deliveries. At airports with multi- at-grade intersections, particularly signalized intersections, ple entrances/exits, this can be accomplished by having one can be improved by providing exclusive left-turn lanes entry/exit serving airline passengers and the other serving non- (thereby eliminating conflicting traffic movements from a passenger traffic. At airports with one access road, this can be signal phase) or adding free-flow right-turn lanes. accomplished by having nonpassenger traffic exit the access roadway well in advance of the terminal area, and by provid- Reconfigure Roadways ing a separate service roadway for these vehicles. Appendix B (Bibliography) lists selected references regarding · Eliminating three-way decision points. It may be possible the design and improvement of roadways and intersections to eliminate a three-way decision point without requiring and relevant design standards and guidelines relevant to air- major roadway reconstruction, by moving one of the deci- ports. These references should be reviewed prior to implement- sion points upstream and thereby converting the three-way ing any roadway improvement, particularly those that require decision point into two separate two-way decision points, the design of new roadways or modification or reconfiguration which is preferable and easier for motorists. of the layout of existing roadways. · Lengthening weaving area. It may be possible to improve an unacceptable weaving operation by closing one exit from the weaving area and directing traffic to a subsequent down- Potential Physical Improvements stream exit leading to the same destination. For example, at to Enhance Roadway Operations Seattle-Tacoma International Airport, traffic operations on Widen Roadways a return-to-terminal roadway were improved by directing recirculating traffic toward the airport exit and then to a Additional roadway capacity can result from the following: path that leads back to the terminal, thereby extending the length of the weaving area. At Los Angeles International · Constructing new lane(s). Additional lanes can be con- Airport, a movable gate arm is used to close a roadway to structed if sufficient available right of way is clear (or if it can traffic on the busiest days of the year, requiring vehicles to be cleared) of obstacles, such as existing or proposed build- follow a slightly longer path, but extending the length of the ings, underground utilities, aviation limit lines (where FAA weaving area. Such improvements can be implemented for restrictions govern acceptable land uses), or other fixed minimal cost (e.g., replacing a roadway directional sign and obstacles. Construction costs and schedules are a function of installing a barrier, if necessary). the roadway alignment, extent and type of construction, · Improving queuing space. Queuing space can be improved obstacles to be relocated (if any), need to maintain and pro- by either providing additional storage space or increasing tect other vehicular and pedestrian traffic during construc- flow rates through the point of constraint. For example at tion, and other factors. the entry or exit of a parking facility, queuing space can be · Reconfiguring existing lanes. Additional lanes can be cre- increased (1) by relocating the gate arms at the entry or con- ated by reducing the widths of existing roadway lanes to trol booths at the exit plaza to provide additional storage form additional lanes. For example, five lanes can be cre- space or (2) by increasing traffic flow rates at the control ated on an existing four-lane roadway by reducing lane point by replacing the existing access control technology widths (e.g., from 13 feet or 12 feet to 11 feet or 10 feet) and (e.g., replacing an existing ticket issuing machine with a by simultaneously reducing the width of, or converting, card reader recognizing employee parking badges, or an roadway shoulders or paved gutter strips into travel lanes. automatic vehicle identification [AVI] transponder on Unless existing drainage structures must be replaced or commercial ground transportation vehicles). For example, relocated, the cost of such reconfiguration is very low. with use of a credit card in/credit card out parking access · Lengthening tapers/correcting lane imbalances. Roadway control system, more vehicles can be processed per lane construction is required to correct inadequate roadway than with a cashier, and the need to print and issue parking tapers or lane imbalances. The length of a roadway taper tickets may be reduced or potentially eliminated. depends on the posted speed. For example, a 250-foot-long taper is required on a 35 mph roadway to add (or end) a Improve Roadway Wayfinding Signs 12-foot-wide travel lane. Providing the required lane bal- ance may require construction of a full lane (upstream or It may be possible to improve roadway guide signs by downstream) for a longer distance. Highway design guides replacing complex, existing signs with simpler signs that can
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62 be more easily understood by motorists. This can be accom- of concrete pavement to create a warning signal (i.e., a rum- plished by attempting to simplify and prioritize the message ble strip) for motorists as they approach a slow-speed area. content, reviewing the text and font, and using standard It is possible to increase the frequency and volume of the phraseology where possible. The use of dynamic message signs warning signal by reducing the distance between successive may also be helpful in certain instances (e.g., parking controls strips. and space availability). · Dynamic warning signs. Radar-activated speed limit signs can be installed to detect the speed of approaching vehicles and indicate to drivers how fast they are traveling. For Construct and Operate Traffic Operations Center vehicles exceeding the posted speed limit, the display could At airports with complex roadway networks and multiple flash red. parking facilities, it may be possible to improve traffic flows by · Automatically activated pedestrian signals. Pedestrians constructing and operating a traffic operations center, simi- crossing a roadway can automatically activate signals embed- lar to those in many large urban areas (see Figure 6-3). Using ded in the roadway pavement. video cameras, traffic detectors, and other technologies, the · Enforcement. Police enforcement measures and tools that traffic operations center allows airport staff to monitor air- are commonly and frequently used in non-airport environ- portwide traffic operations, direct airport traffic officers to ments can be used to enforce posted speeds, including park- congestion points, close or open parking facilities or road- ing police vehicles in a visible location. ways, change advisory signs, and perform other operations to improve the flow of traffic. Transportation Demand Management When used in an urban or regional setting, transportation Potential Operational Measures to Enhance demand management (TDM) measures are used to discourage Roadway Operations single-occupant, private vehicle trips by promoting ride- Speed Reduction Measures sharing or the use of public transit, and to encourage motorists to drive outside peak hours. At airports, the most productive It may be necessary to encourage motorists to decelerate as application of TDM is to encourage airport employees to share they approach the terminal area, particularly at airports where rides or use public transit to reduce the number of vehicle trips. a limited access highway connects the regional roadway net- For example, some airport operators and other employers have work with the terminal area roadways. established work schedules that call for employees to work 9 Measures to encourage motorists to obey posted speed lim- out of every 10 days (e.g., take every other Friday off by work- its and slow down as they approach the terminal area include ing longer hours on other days). Other airport operators offer discounted transit passes or partially subsidize the commuting · Pavement texture. Contrasting pavement textures (e.g., expenses of employees who agree to use transit and forego the brick, cobblestone, or gravel textures) can be cast into strips use of parking facilities. Intelligent Transportation Systems A variety of intelligent transportation system (ITS) applica- tions are available to encourage the efficient and safe use of transportation facilities. At airports these applications include pricing mechanisms (increasing parking costs), the use of AVI and global positioning system (GPS) technologies to monitor the location and number of trips made by commercial vehi- cles or shuttle buses, and a variety of systems for distribut- ing traveler information to arriving motorists (e.g., airline schedules/delays and parking space availability). Traveler information can be distributed using the Internet, mobile tele- phones, highway advisory radios, flight information display systems (e.g., those located on deplaning curbsides or within cell phone lots), or dynamic signage presenting parking Figure 6-3. Transportation operations center at space availability information or warning overheight vehi- Frankfurt Airport. cles approaching areas with limited vertical clearance.