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OCR for page 69
69
Table A-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
Method, the Contract Service Dependability Method, the implemented at some APM systems. The method is very
System Service Availability Method, and the Paris Airport similar to the System Dependability Method in that it incor-
Authority Method. These methods are primarily distinguished porates the same three performance measures: reliability,
from one another by the number of factors measured, grace maintainability, and availability. While the older literature
period durations, whether credit is allowed for partial service revealed that this method previously relied on three sets
operations during failures, and whether capacity is a consider- of the RAM measures (one set called "absolute" RAM, one
ation in any of the measures. The methods and characteristics called "design/operational" RAM, and another called "con-
of each are summarized in Table A-1. tract service" RAM), it has today generally evolved into two
Each of the applied methods is described in detail in the measure sets--one RAM set where all failures are taken into
following. account and another RAM set where failures that are consid-
ered exceptions are not taken into account. This method gen-
erally allows for a grace period of 3 min or less for downtime
2.2.1.1 System Dependability Method
resulting from incidents/failures.
The classical measurement of performance for systems Concerning the method's treatment of partial service
in general, as well as in the APM industry, is the System credit and capacity considerations, most of the examples of
Dependability Method, as presented in ASCE 21-05, Ameri- this method revealed that these are not incorporated as part
can Society of Civil Engineers, Automated People Mover of the method. There were two exceptions, however. The first
Standards Part 1, Chapter 4 [2.2.1]. This method incorporates exception is the method as applied to the pinched loop APM
three measures of overall system performance: reliability, or system at Chicago's O'Hare International Airport. There, the
mean time between failure; maintainability, or mean time system has the capability to operate around many types of
to restore; and availability (the ratio of MTBF to the sum of failures because its numerous switches and routing combi-
MTBF and MTTR). This method allows for the consideration nations, as well as its bidirectional capability, provide a high
of grace periods for downtime incurred as a result of an inci- degree of flexibility. As such, partial service credit is allowed,
dent or failure, and it also allows for downtime credit during and system capacity is considered only so far as to make the
partial service operations. Capacity is not considered as part calculation of the credit [2.2.3 and 2.3.4]. The formula is
of this method. complicated by the fact that the Chicago system can operate
with various train lengths, which forces the consideration of
both transportation capacity and headway as well as a cor
2.2.1.2Contract Service
responding set of specific rules. This is not so in the case of the
Dependability Method
Paris Airport Authority Method that will be discussed later.
The Contract Service Dependability Method was devel- The second exception is the method as applied to the shut-
oped by U.S. consulting firm JKH Mobility and has been tle APM at Orlando International Airport [2.2.10]. Although
