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20 Chapter 4 Performance Measurement of APM Systems at Airports: The Current Situation Research of several industry documents shows that current 18.104.22.168 System Dependability Method performance measurement of both airport and non-airport The classical measurement of performance for systems in APMs is primarily focused on traditional measures of op- general, as well as in the APM industry, is the System Depend- erating system performance (i.e., reliability, maintainability, ability Method, as presented in ASCE 21-05, American Society and availability). Other APM performance measures related of Civil Engineers, Automated People Mover Standards-- to economic efficiency, comfort, and convenience, among Part 1, Chapter 4. This method incorporates three measures others, have received significantly less attention in the lit- of overall system performance: reliability, or mean time be- erature, if any at all. Some of these measures are applied in tween failure (MTBF); maintainability, or mean time to restore other industries, however, and have been considered in the (MTTR); and availability (the ratio of MTBF to the sum of development of the performance measures set forth in this MTBF and MTTR). This method allows for the consideration guidebook. of grace periods for downtime incurred as a result of an inci- dent or failure, and it also allows for downtime credit during 4.1Historical Performance partial service operations. Capacity is not considered as part Measurement of APM of this method. Systems at Airports The documented methods of system performance mea- 22.214.171.124 Contract Service Dependability Method surement for airport APMs can be broadly divided into two The Contract Service Dependability Method was developed classes: applied methods and theoretical methods. These clas- by U.S. consulting firm JKH Mobility and has been imple- sifications are described in the following subsections. mented at some APM systems. The method is very similar to the System Dependability Method in that it incorporates 4.1.1 Applied Methods the same three performance measures: reliability, maintain- ability, and availability (RAM). While the older literature In general, there are four applied methods used in air- revealed that this method previously relied on three sets of port APM performance measurement: the System De- the RAM measures (one set called "absolute" RAM, one called pendability Method, the Contract Service Dependability "design/operational" RAM, and another called "contract ser- Method, the System Service Availability Method, and the vice" RAM), it has today generally evolved into two measure Paris Airport Authority Method. These methods are pri- sets--one RAM set where all failures are taken into account marily distinguished from one another by the number of and where failures that are considered exceptions are not factors measured, grace period durations, whether credit is taken into account. This method generally allows for a allowed for partial service operations during failures, and grace period of 3 min or less for downtime resulting from whether capacity is a consideration in any of the measures. incidents/failures. The methods and characteristics of each are summarized Concerning the method's treatment of partial service credit in Table 1. and capacity considerations, most of the examples of this Each of the applied methods is described in detail in the method revealed that these are not incorporated as part of following. the method. There were two exceptions, however. The first
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21 Table 1. APM performance measurement, applied methods. Partial No. of Grace Capacity Method/Measures Service Measures Period Considered Credit System Dependability Method Reliability Maintainability 3 yes optional no Availability Contract Service Dependability Method Contract service reliability 3 Contract service maintainability 3 no* no* min Contract service availability System Service Availability Method Service mode reliability Service mode maintainability 1 Service mode availability 6 head- yes yes Fleet availability way Station platform door availability System service availability Paris Airport Authority Method Contract service availability 1 no yes yes** *In most cases of the literature reviewed. **During degraded mode operations. is the method as applied to the pinched-loop APM system system service (i.e., train stoppages), other failures that affect at Chicago's O'Hare International Airport. There, the system passenger service without interrupting system service are not has the capability to operate around many types of failures captured. For example, station platform door failures that because its numerous switches and routing combinations, deny passengers access to the vehicles affect passenger service as well as its bidirectional capability, provide a high degree and may not be reflected in the measures of the other meth- of flexibility in maintaining service during failures. As such, ods. This method incorporates measures of service mode avail- partial service credit is allowed, and system capacity is con- ability, fleet availability, station platform door availability, and sidered only so far as to make the calculation of the credit. system service availability. The additional availability measures The formula is complicated by the fact that various train related to fleet and station platform doors ensure that all fail- lengths may be operating at the same time, which forces the ures affecting passengers (not just those that interrupt service) consideration of both transportation capacity and headway are reflected in the overall service availability measure. as well as a corresponding set of specific rules. This is not so The System Service Availability Method also tracks the in the case of the Paris Airport Authority Method that will be number of service mode failures, or downtime events, which discussed later. allows measures of service mode reliability and maintainabil- The second exception is the method as applied to the dual- ity to be easily made. These two measures, along with the four lane shuttle APM at Orlando International Airport. Although availability measures described previously, make up the six capacity is normally not considered in this exception at all, a measures unique to this method. type of partial service credit is allowed in one specific case-- This method allows an equivalent of one headway dura- during a failure of the scheduled single train/lane operation tion or less for a grace period for both incidents/failures and when the standby train/lane is undergoing maintenance and schedule transitions. It also allows for the consideration of is unavailable. downtime credit for partial service operations provided dur- ing failures, and it considers capacity as part of its normal measure set rather than during partial service credit only. 126.96.36.199 System Service Availability Method The System Service Availability Method has been advocated 188.8.131.52 Paris Airport Authority Method and used by U.S. consulting firm Lea+Elliott since 1994. As a result, it is in wide usage at airport APMs worldwide. The The Paris Airport Authority (Aeroports de Paris) Method is method is distinguished from the other methods by measures a variation on the System Dependability Method discussed pre- that record the performance of subsystems that are most viously. It was introduced by Aeroports de Paris and ALONEX likely to affect passengers. Because the other methods con- for Line 1 of the APM system at Roissy Charles-de-Gaulle centrate only on performance as affected by interruptions to (CDG) Airport. Unlike the other methods, it calculates con-