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81 For more information on conducting an O&D survey, please imbedded loops to provide the share of traffic by private refer to ACRP Report 26: Guidebook for Airport-User Survey automobiles and other vehicles not tracked by the AVI sys- Methodologies, which is the guidebook developed in support of tem, which includes maintenance vehicles, rental cars, and ACRP Project 03-04. (21) "nontenant" commercial vehicles. Traffic counters and AVI readers should be located in the same areas to ensure that the data are comparable. Vehicle Activity and Vehicle Numbers and types of commercial vehicles can be estimated Occupancy Counts through other tracking mechanisms, such as taxicab and For airports with congested roadway and curbside systems, limousine dispatch counts and HOV schedules, if an AVI the airport operator may want to understand if parking system is not available. strategies have caused a mode shift that resulted in a diversion Manual vehicle classifications by mode can be obtained. Per- of vehicle traffic from the curbside (i.e., passenger pickup and sonnel with handheld computer devices or clipboards would drop-off ) to the parking facilities or vice versa. Although be stationed at different points on the roadway and terminal some airport operations personnel may have an intuitive feel curbsides to count vehicles by a variety of classifications. for this information, supporting data are derived either through an O&D passenger survey, as described in the previ- These methods to capture mode distribution do not allow ous section, or estimated from a variety of data sources. The for the classification of rental cars and private automobiles. latter approach will require the distillation of data from dif- Activity at a terminal curbside that appears to be generated by ferent sources and time periods, and supplemental data from private automobile will typically include (1) rental car cus- manual or automated traffic counts. Vehicle count data by tomers dropping off members of their travel party at the curb- mode and data on the number of occupants by mode are nec- side prior to returning the rental car, (2) long-term parkers and essary for estimating airline passenger mode share. short-term parkers dropping off members of their travel party Although some airports use automatic vehicle identifica- prior to parking the automobile, (3) recirculating vehicles that tion (AVI) systems to collect detailed activity data associated make multiple passes of the curbside in advance of meeting with commercial vehicle traffic using the airport curbsides, passengers for pickup, and (4) bypassing vehicles accessing an these systems track only those vehicles that are mounted with adjacent terminal that drive past the terminal while traveling to a radio-frequency-based transponder. However, these AVI or from the adjacent terminal. An O&D survey is more effec- data, in combination with roadway traffic counts of all vehi- tive at estimating the share of parking customers versus those cles accessing the airport, have been used to obtain estimates that are picking up and dropping off passengers, and estimat- of private automobiles and other vehicles that are not tracked ing the share of rental cars versus private automobiles. by the AVI system. Finally, nonpassenger vehicles at the terminal curbsides, such as enforcement personnel, employees, airport mainte- nance, and delivery vehicles, will be captured in the non-AVI Vehicle Traffic Generated by Mode automatic traffic counts and will need to be separated from the Automatic traffic recorders (ATRs) can be temporarily vehicle traffic related to airline passengers. Only some of this installed on the airport roadway system, including the termi- vehicle traffic can be identified through a manual classification nal curbsides, parking access roadways, recirculation road- count. ways, and in the vicinity of cell phone lots to collect vehicle counts for time periods before and after implementation of Vehicle Occupancy Counts a strategy. Permanent count stations using imbedded loop detectors or other technology also have been installed by some Vehicle counts may provide a distribution of vehicles by airport operators interested in obtaining an ongoing database vehicle type or mode, but vehicle occupancy is necessary to of traffic activity. These traffic counting systems can be config- estimate a passenger mode-share distribution. If not estimated ured to estimate vehicle classification based on the number of through an O&D survey, manual counts can be conducted axles per vehicle, but are limited in their ability to identify spe- before and after implementation of a strategy. Manual vehicle cific modes. Other means can be used to collect mode-specific occupancy counts can be conducted through observations-- distribution to supplement the vehicle counts as follows: personnel with handheld computer devices or clipboards stationed at different points on the roadway and terminal An AVI system tracks trips by commercial vehicles that have curbsides, counting occupants or numbers of passenger entries been mounted with a radio-frequency-based transponder and exits per vehicle by vehicle classification. This count should (e.g., toll tag) and can provide the commercial vehicle dis- be conducted as part of the vehicle classification count. Com- tribution by mode for all vehicles affixed with transpon- mercial vehicle operators could be recruited to keep a log of ders. Commercial vehicle trips can be subtracted from the the numbers of passengers per vehicle during the same time total traffic counts obtained using ATRs or permanent period.