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78 their connecting flights. Similarly, passengers prefer adequate and anxious. Maximum wait time as a measure of passenger personal space on platforms and trains. Periodic monitoring service for airport APM systems is a reasonable extension of of the wait times and personal space allocations may be use- the IATA wait-time guidelines. ful to be sure that passengers have a comfortable experience Similarly, IATA recommends level-of-service and space stan- using the APM. dards for many airport facilities, such as check-in and baggage claim areas. Level-of-service standards can be defined for air- port APM platforms and vehicles as a means of comparing the 2.4.3 Other Airport Agency Measures level of service provided by different systems or for determining Agencies operating at airports, such as immigration ser- when additional trains are required. vices, have performance criteria they use to determine proper In addition, John J. Fruin's Pedestrian Planning and Design staffing levels and space requirements. International airport [2.4.7] provides recommendations for personal space alloca- organizations also have defined standards for performance to tion and has become a handbook for designers and planners. be used in the planning and monitoring of the immigration Fruin's level-of-service standards are based on a six-point services function. scale, with "A" being the best level of service and "F" being The International Air Transport Association (IATA) defines unacceptable service. level-of-service space requirements for passport control [2.4.8], while the International Civil Aviation Organization (ICAO) 2.5Highway Performance has standards for the processing of passengers from an arriving Measurement aircraft [2.4.9]. Immigration agencies have also set standards for how long passengers wait for immigration processing and This section is a summary of the key findings of perfor- how much space they should be allocated. mance measurement as it relates to the highway industry on As discussed in the previous section, the wait time and the national level. Three areas are discussed in this section: per- personal space allocation measures are relevant to airport formance measurement activities of the FHWA, the National APM systems. Just as the immigration services consider the Transportation Operations Coalition, and a review of NCHRP passenger wait times and space allocation in monitoring per- Project 3-68, "Guide to Effective Freeway Performance Mea- formance, airport APM system operators may benefit from surement" (the final report for which was produced as NCHRP applying these same types of performance measures. Web-Only Document 97: Guide to Effective Freeway Performance Measurement) [2.5.6]. 2.4.4Design Recommendations, Standards, and Levels of Service 2.5.1FHWA Performance Measurement Program Finally, there are level-of-service recommendations used by airport developers, planners, and designers that, while not The FHWA's Office of Operations supports a performance expressly intended as performance measures, can be used to measurement program focused on system (highway) perfor- gauge and compare the efficiency and performance of airport mance as it relates to mitigation of congestion. The program facilities. For example, the Airport Development Reference measures the sources and consequences of congestion, and Manual published by IATA is frequently used as a guide for the effectiveness of operations strategies to reduce that those planning new or expanding existing airport facilities. congestion [2.5.5]. While the manual presents recommendations, they have, Some examples of congestion performance measures in fact, come to be viewed as standards [2.4.8]. that can be used by highway agencies to monitor trends are Perhaps the most relevant recommendations presented in provided in Table A-2. the manual for airport APM applications are those pertain- While many of these metrics may be useful in the highway ing to walk distances, wait times, and space occupancy. For industry, one of the principles that the FHWA has established example, IATA recommends that the maximum unassisted for monitoring congestion is that meaningful congestion walking distance between major airport functions be 300 m. performance measures must be based on the measurement In assessing airport APM system designs or comparing one of travel time. The reason for this is that travel time is easily system to another, the maximum walk distance can be used as understood by a wide variety of audiences--both technical a measure of the level of passenger service provided. and nontechnical--and it can be used from both a user and The waiting time guidelines recommended by IATA for owner/agency perspective. In particular, the FHWA has various airport facilities are akin to passenger wait time for identified travel time reliability and its associated measures an APM train. The idea is to set a maximum wait time as a as the most effective measures of (highway) system perfor- standard so that passengers do not become uncomfortable mance from the user's perspective [2.5.5]. As a result, this

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79 Table A-2. Examples of congestion performance measures used by highway agencies. Performance Metric Definition/Comments Throughput Vehicle miles of travel (VMT) Vehicle miles of travel is the number of vehicles on the system times the length of highway they travel. Truck-vehicle miles of travel Person miles of travel is used to adjust for the fact Person miles of travel that some vehicles carry more than a driver. Average Congestion Conditions The average speed of vehicles measured between Average travel speed two points. The time it takes for vehicles to travel between two Travel time points. Both travel time and average travel speed are good measures for specific trips or within a corridor. Number and percent of trips with travel times > (1.5 average travel time) Thresholds of 1.5 and 2.0 times the average may be adjusted to local conditions; additional thresholds Number and percent of trips with may also be defined. travel times > (2.0 average travel time) Ratio of actual travel time to an ideal (free-flow) Travel time index travel time. Free-flow conditions on freeways are travel times at a speed of 60 mph. Total delay (vehicle hours and person hours) Delay is the number of hours spent in traffic beyond Bottleneck (recurring) delay (vehicle hours) what would normally occur if travel could be done at Traffic incident delay (vehicle hours) the ideal speed. Work zone delay (vehicle hours) Determining delay by source of congestion requires Weather delay (vehicle hours) detailed information on the nature and extent of events (incidents, weather, and work zones) as well Ramp delay (vehicle hours and person hours; as measured travel conditions. where ramp metering exists) Delay per person Delay per person and delay per vehicle require knowledge of how many vehicles and persons are Delay per vehicle using the roadway. Percent of VMT with average speeds <45 mph Percent of VMT with average speeds <30 mph Percent of day with average speeds <45 mph These measures capture the duration of congestion. Percent of day with average speeds <30 mph Reliability The 95th percentile of a distribution is the number above which only 5% of the total distribution Planning time (computed for actual travel time remains. That is, only 5% of the observations exceed and the travel time index) the 95th percentile. For commuters, this means that for 19 out of 20 workdays in a month, their trips will take no more than the planning time. Ratio of the 95th percentile (planning time) to the Planning time index (computed for actual travel ideal or free-flow travel time (the travel time that time and the travel time index) occurs when very light traffic is present--about 60 mph on most freeways). Represents the extra time (buffer) most travelers add Buffer index to their average travel time when planning trips. For a specific road section and time period: 95th percentile travel time average travel time Buffer index (%) = average travel time Source: [2.5.1]