ISO/TS 17444-1:2012

TECHNICAL ISO/TS
SPECIFICATION 17444-1
First edition
2012-10-01
Electronic fee collection — Charging
performance —
Part 1:
Metrics
Perception du télépéage — Performance d’imputation —
Partie 1: Métrique
Reference number
©
ISO 2012
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ii © ISO 2012 – All rights reserved

Contents Page
Foreword .iv
Introduction . v
1 Scope . 1
2 Normative references . 2
3 Terms and definitions . 3
4 Abbreviated terms . 7
5 Definition of charging performance metrics . 7
5.1 General . 7
5.2 Metric Identification . 11
5.3 End-to-End metrics . 11
5.4 User Account Metrics .12
5.5 Payment Claim Metrics .13
5.6 Billing Details Metrics .13
5.7 Toll Declaration Metrics .15
5.8 Charge Report Metrics .18
Annex A (informative) Defining Performance Requirements .21
Bibliography .24
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
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The main task of technical committees is to prepare International Standards. Draft International Standards
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International Standard requires approval by at least 75 % of the member bodies casting a vote.
In other circumstances, particularly when there is an urgent market requirement for such documents, a technical
committee may decide to publish other types of document:
— an ISO Publicly Available Specification (ISO/PAS) represents an agreement between technical experts in
an ISO working group and is accepted for publication if it is approved by more than 50 % of the members
of the parent committee casting a vote;
— an ISO Technical Specification (ISO/TS) represents an agreement between the members of a technical
committee and is accepted for publication if it is approved by 2/3 of the members of the committee
casting a vote.
An ISO/PAS or ISO/TS is reviewed after three years in order to decide whether it will be confirmed for a further
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Standard or be withdrawn.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO/TS 17444-1 was prepared by Technical Committee ISO/TC 204, Intelligent transport systems, and by
Technical Committee CEN/TC 278, Road transport and traffic telematics in collaboration.
ISO 17444 consists of the following parts, under the general title Electronic fee collection — Charging performance:
— Part 1: Metrics [Technical Specification]
1)
— Part 2: Examination framework
1) To be published.
iv © ISO 2012 – All rights reserved

Introduction
Electronic Tolling systems are complex distributed systems involving critical technology such as dedicated
short-range communication (DSRC) and global navigation satellite systems (GNSS) both subject to a certain
random behaviour that may affect the computation of the charges. Thus, in order to protect the interests of the
different involved stakeholders, in particular Service Users and Toll Chargers, it is essential to define metrics
that measure the performance of the system as far as computation of charges is concerned and ensure that
the potential resulting errors in terms of size and probability are acceptable. These metrics will be an essential
tool when establishing requirements for the systems and also for examination of the system capabilities both
during acceptance and during the operational life of the system.
In addition, in order to ensure the interoperability of different systems it will be necessary to agree on common
metrics to be used and on the actual values that define the required acceptable performances, although this is
not covered in this part of ISO/TS 17444.
Toll schemes take on various forms as identified in ISO/TS 17575 (all parts) and ISO 14906. In order to create
a uniform performance metric specification, toll schemes are grouped into two classes, based on the character
of their primary charging variable: Charging based on discrete events (charges when a vehicle crosses or
stands within a certain zone), and those based on a continuous measurement (duration or distance).
The following are examples of discrete (event-based) toll schemes.
— Single object charging: a road section, bypass, bridge, tunnel, mountain pass or even a ferry, charged per
passage; most tolled bridges belong to this category.
— Closed road charging: a fixed amount is charged for a certain combination of entry and exit on a motorway
or other closed road network; many of the motorways in Southern Europe belong to this category.
— Discrete road links charging: determined by usage of specified road links, whether or not used in their entirety.
EXAMPLE German heavy goods vehicle (HGV) charge.
— Charging for cordon crossing: triggered by passing in or out through a cordon that encircles a city
core, for example.
EXAMPLE Stockholm congestion charging.
The following are examples of continuous toll schemes.
— Charging based on direct distance measurement: defined as an amount per kilometre driven.
EXAMPLE Switzerland’s HGV charge; US basic vehicle miles travelled approach.
— Charging based on direct distance measurement in different tariff zones or road types: defined as an
amount per kilometre driven, with different tariffs applying in different zones or on different road types. This
is a widely discussed approach, also known as Time-Distance-Place charging, and is under consideration
in many European countries. The pilot programme in Oregon is an example from North America.
— Time in use charge: determined by the accumulated time a vehicle has been in operation, or, alternatively,
by the time the vehicle has been present inside a predefined zone.
In all these examples of toll schemes, tolls may additionally vary as a function of vehicle class characteristics
such as trailer presence, number of axles, taxation class, operating function, and depending on time of day or
day of week, so that, for example, tariffs are higher in rush hour and lower on the weekends.
With this degree of complexity, it is not surprising to find that the attempts to evaluate and compare technical
solutions for Service User charging have been made on an individual basis each time a procurement or study
is initiated, and with only limited ability to reuse prior comparisons made by other testing entities.
The identification of different types of schemes as proposed in ISO/TS 17575 (all parts) and their grouping in
the mentioned two classes is described in Table 1, which also identifies the examples mentioned above.
Table 1 — Tolling scheme designs grouped according to Scheme categories
Examples Scheme type ISO/TS 17575 category
Single object charging Discrete Sectioned roads pricing
Closed road charging Discrete Sectioned roads pricing
Discrete road links charging Discrete Sectioned roads pricing
Charging for cordon crossing Discrete Cordon pricing
Time in use charge Continuous Area pricing – time
Cumulative distance charge Continuous Area pricing – distance
Charging for cumulative distance (or time) in different zones Continuous Area pricing – distance
(or by road type)
No toll schemes are purely continuous. At the very least, a system must be able to stop accumulating charges
when it leaves a jurisdiction in which a charge is due, and resume charging when it returns or enters another.
Additionally, many Charging Schemes are set up so that the tariff is modified using discrete parameters, such
as spatial zones, time spans, vehicle classes, etc. Under those circumstances, each unit of distance or time
costs a different amount depending, for example, on whether it takes place inside or outside an area, such as
a city, whether a trip takes place in rush hour or at night, or depending on what type of vehicle is used. In this
part of ISO/TS 17444 references to a “continuous system” have to be understood as those systems having
some continuous behaviour even though they may also integrate some discrete nature. References to “discrete
systems” are limited to those systems that are purely discrete.
In these schemes, all the discrete parts (zones, cordons, events, time, vehicle class, etc.) that a system has
to identify are translated into a particular tariff (e.g. price per kilometre) that has to be applied to the measured
continuous variable (e.g. travelled kilometres) resulting in another continuous parameter, money.
Among the different Interoperability Application Profiles defined in CEN/TS 16331, only Section Road Tolling
has a purely discrete nature while the other four profiles have both discrete and continuous natures.
Some features of discrete and continuous toll schemes that are of relevance for the definition of metrics
proposed in this part of ISO/TS 17444 are analysed below.
Discrete toll schemes
In a discrete toll scheme, distinct events are associated with the identification of Charge Objects. It can be
that a vehicle crossed a cordon, passed a bridge, was present in an area, or in an area on a given day. An
event that takes place can either be correctly recorded by the system or can be missed. However, there is also
the possibility that an event is recorded even though it did not actually take place. This is summarized in the
following matrix in Table 2.
Table 2 — Theoretical event decision matrix for discrete schemes
System detects Chargeable Event
Event Matrix
Yes No
Missed Recognition
Correct
Yes
Charging
(Undercharging)
Chargeable Event takes
place
False Positive
Correct
No
Non-charging
(Overcharging)
In this matrix there are two successful scenarios (Correct Charging and Correct Non-charging), and two
unsuccessful (Missed Recognition and False Positive). The unsuccessful scenarios have very different
consequences. A Missed Recognition, i.e. a Chargeable Event that takes place but is not recorded by the
system, implies an undercharging, as the Service User is not charged.
vi © ISO 2012 – All rights reserved

In the case of False Positive, a vehicle that is not using the toll domain is being charged for an event which did
not take place. This implies an overcharging which is in violation of the legal rights of the Service User, and
ultimately risks eroding trust in the system.
This part of ISO/TS 17444 therefore makes a distinction between the two types of errors and defines associated
metrics to protect the interests of the Toll Charger and Service Users in terms of the allowed probabilities of
those events.
Continuous toll schemes
A continuous toll scheme is one where the charge is calculated using accumulated time or distance the base
tariff is applied to.
Note that a discrete scheme with a large number of Charge Objects would lead to charging incremental
variations, and is hence approaching a continuous scheme (the higher the number of events, the closer such
schemes are to a continuous scheme). In any case, this would still formally be a discrete scheme.
In discrete toll schemes errors are binary: either a Charge Event is correctly recorded or it is not. However, in
continuous schemes the errors are relatively small and they vary continuously, i.e. those errors are real (in the
mathematical sense) variables instead of logical variables. Figure 1 shows different levels of dispersion and
different directions of bias. The horizontal axis shows the size of the errors and the vertical axis the probability
density. The vertical line in each plot represents zero charging error. Note that it is possible to have small
dispersion (i.e. a small standard deviation) that still biases charging high or low (i.e. not accurate).
AB
Charging Error Charging Error
CD
Charging Error Charging Error
Figure 1 — Idealized plots of error distribution of four different result sets
In Figure 1 Chart A symbolizes the results from a Front End with more dispersion than that used for Chart B.
For all parties involved, B is preferable to A. Charts C and D show two Front Ends with the same standard
deviation, but where Chart C shows one that is consistently undercharging, and D one that is consistently
overcharging road usage.
Probability
Probability
Probability Probability
By defining an Accepted Charging Error Interval to the chart, with a lower and an upper bound, as shown in
Figure 2, it is possible to state that for a system to be accepted it must perform so that some minimum share of
the measurements fall inside the interval specified as accepted by the Toll Charger.
Accepted Error Interval
Charging Error
Figure 2 — Definition of Accepted Error Interval
Setting the upper and lower bounds far apart relaxes requirements on the equipment evaluated, while setting
them closer together would make the requirement to fulfil harder to pass. By setting the upper bound closer to
the correct charging value and the lower bound farther away, the Toll Charger can formalize exactly how much
more important it is to avoid overcharging than it is to avoid undercharging. By defining those bounds (Accepted
Charging Error Interval) together with the probabilities to be inside and above those bounds the Toll Charger can
define precisely its requirements distinguishing between overcharging and undercharging. In reality no scheme
is purely continuous and all foreseeable continuous schemes have some discrete components. The discrete
nature of real systems can be either associated to the physical border of a country (continuous measurements
take place only if vehicle is within the country) or to the identification of different urban zones or roads where
different tariffs (per unit of time or distance) are applied.
Thus, continuous schemes will have associated metrics that are specific to those continuous systems but the
ones identified for discrete schemes will also be applicable.
viii © ISO 2012 – All rights reserved
Probability Density
Lower Bound
Correct Charging
Upper Bound
TECHNICAL SPECIFICATION ISO/TS 17444-1:2012(E)
Electronic fee collection — Charging performance —
Part 1: Metrics
1 Scope
This part of ISO/TS 17444 defines metrics for the charging performance of electronic fee collection (EFC)
systems in terms of the level of errors associated with charging computation.
This part of ISO/TS 17444 is a toolbox standard of metrics. The detailed choice of metrics depends on the
application and the respective context.
This part of ISO/TS 17444 describes a set of metrics with appropriate definitions, principles and formulations,
which together make up a reference framework for the establishment of requirements for EFC systems and
their later examination of the charging performance.
The charging performance metrics defined in this part of ISO/TS 17444 are intended for use with any Charging
Scheme, regardless of its technical underpinnings, system architecture, tariff structure, geographical coverage,
or organizational model. They are defined to treat technical details that may be different among technologies
and vendors or vary over time as a “black box”.
They focus solely on the outcome of the charging process – i.e. the amount charged in relation to a pre-
measured or theoretically correct amount – rather than intermediate variables from various components as
sensors, such as positioning accuracy, signal range, or optical resolution. This approach ensures comparable
results for each metric in all relevant situations.
The metrics are designed to cover the information exchanged on the Front End interface and the interoperability
interfaces between Toll Service Providers, Toll Chargers and Road Users as well as on the End-to-End level.
Metrics on the following information exchanges are defined:
— Charge Reports;
— Toll Declarations;
— Billing Details and associated event data;
— Payment Claims on the level of user accounts;
— User Accounts;
— End-to-End metrics which assess the overall performance of the charging process.
The details on the rationale of this choice are described in 5.1.
The proposed metrics are specifically addressed to protect the interests of the actors in a toll system, such as
Toll Service Providers, Toll Chargers and Road Users. The metrics can be used to define requirements (e.g.
for requests for proposals) and for performance assessment.
This part of ISO/TS 17444 recognizes two types of situations where a performance assessment is necessary:
a) when an assessment is carried out during a limited time span, such as when formulating requirements and
assessing systems for acquisition purposes, conducting acceptance testing as part of the commissioning
process, or as part of a certification procedure. Any one of these types of assessment is referred to as
an evaluation;
b) when an assessment is needed as an ongoing supervision process, throughout the lifetime of a system, in
order to validate contracted service levels, to identify fraud or malfunction, or to support ongoing maintenance
and performance improvement processes. This type of assessment is referred to as monitoring.
NOTE 1 Definitions and metrics proposed in this part of ISO/TS 17444 are intended for both situations.
The following are not covered by this part of ISO/TS 17444.
— This part of ISO/TS 17444 does not propose specific numeric performance bounds, or average or worst-
case error bounds in percentage or monetary units. Those decisions are left to the Toll Charger (or to
agreements between Toll Charger and Service Provider), while providing a way to be sure that there
is a consistent framework for describing system requirements when writing Request for proposals, for
system comparisons during acquisition, for test results, for Service Level Agreements, and ongoing (post-
deployment) performance monitoring.
— This part of ISO/TS 17444 does not consider the evaluation of the expected performance of a system
based on modelling and measured data from trial at another place.
— This part of ISO/TS 17444 does not consider the specification of a common reference system which would
be required for comparison of performance between systems.
— This part of ISO/TS 17444 does not specify metrics on parts of tolling systems other than the charging
process chain, such as:
— enforcement system;
— security measures.
— This part of ISO/TS 17444 does not cover metrics on parts of the charging processing chain which are
considered an internal matter of one of the interoperability partners:
— equipment performance, e.g. for on-board equipment, road-side equipment or data centres such as
signal range, optical resolution or computing system availability;
— position performance metrics: The quality of data generated by position sensors is considered as an
internal aspect of the Front End. It is masked by correction algorithms, filtering, inferring of data and
the robustness of the Charge Object recognition algorithms.
Even though some of these aspects have a direct impact on charging performance, they are not considered
explicitly in this part of ISO/TS 17444.
NOTE 2 While the Front End interface is considered as internal to the Toll Service Provider domain of responsibility,
it is still covered by metrics. There are two reasons for this exception: firstly a set of standards [ISO/TS 17575 (all parts)]
exists on this interface and secondly the information exchanged on this interface is also part on the TSP-TC interface
(ISO 12855) and therefore metrics are needed.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced document
(including any amendments) applies.
ISO 14906, Electronic fee collection ― Application interface definition for dedicated short-range communication
ISO 17573, Electronic fee collection ― Systems architecture for vehicle-related tolling
ISO 12855, Electronic fee collection ― Information exchange between service provision and toll charging
ISO/TS 17575-1, Electronic fee collection ― Application interface definition for autonomous systems ―
Part 1: Charging
2 © ISO 2012 – All rights reserved

3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
Absolute Charging Error
difference between the measured charge (toll) value and the actual value (as measured by a reference system)
NOTE A positive error means that the measurement exceeds the actual one.
3.2
Accepted Charging Error Interval
interval of the Relative Charging Error varying from a negative (undercharge) to a positive (overcharge) value
that the Toll Charger considers as acceptable, i.e. correct charging
3.3
average relative charging error
ratio between the sum of computed charges associated to a set of vehicles during a certain period of time and
the actual due charge (for the same set of vehicles and the same period) minus 1
3.4
Billing Detail
for a given Transport Service, all necessary data required to determine and/or verify the amount due for
the Service User
NOTE 1 If the data is accepted by both the Toll Charger and the Toll Service Provider, then it is called a concluded
Billing Detail which can be used to issue a Payment Claim.
NOTE 2 For a given Transport Service, the Billing Detail is referring to one or several valid Toll Declaration(s). A valid
Billing Detail has to fulfil formal requirements, including security requirements, agreed between the Toll Service Provider
and the Toll Charger.
[ISO 12855:2012, definition 3.1]
3.5
Chargeable Event
event in which a vehicle passes through a Charge Object that implies that vehicle has to be charged or a
different rate (e.g. price per kilometre) applied
NOTE This event refers to the use of a certain object and not to the mechanisms by which detection is produced.
3.6
Charge Object
any object that is part of the toll context description that may be charged for its use under certain conditions
NOTE Adapted from ISO/TS 17575-1:2010.
3.7
Charging Period
period of time which is used to define the frequency of the Toll Declarations, when Charge Reports are
aggregated to form Toll Declarations
NOTE If the Charging Period is set to 24 hrs then in the Toll Context Data a single Toll Declaration is submitted for
each 24 hr period for each Service User.
3.8
Charge-Relevant Event
event occurring within a tolling system, which is relevant for charge calculation, but not for the detection of a
Charge Object itself
NOTE Examples of this type of event are changes in vehicle category or time zone.
3.9
Charge Report
data structure transmitted from the Front End to the Back End to report road usage data and supplementary
related information
NOTE In 2009/750/EC Charge Report is referred as “Toll Declaration”.
[ISO 12855:2012, definition 3.2]
3.10
discrete toll scheme
toll scheme where the charge is calculated based on distinct events associated with the identification of Charge
Objects such as crossing a cordon, passing a bridge, being present in an area, etc.
NOTE Each event is associated with a certain charge.
3.11
continuous toll scheme
toll scheme where the charge is calculated based on the accumulation of continuously measured parameter(s),
such as distance, time, etc.
3.12
Event Detection
element of the system responsible for detecting Chargeable Events associated with a Charge Object
NOTE The output of this element provides the key information to compute a charge in a discrete scheme, or act as
input for a function in a continuous scheme (e.g. for zones where distance tariffs apply).
3.13
evaluation
process applied for measuring a specific metric or set of metrics during an evaluation phase
3.14
Front End
part(s) of the toll system where road usage data for an individual Road User are collected, processed and
delivered to the Back End
NOTE The Front End comprises the on-board equipment and an optional proxy.
[ISO/TS 17575-1:2010, definition 3.13]
3.15
False Positive Event
Chargeable Event that did not take place but is recorded by the system
3.16
Missed Recognition Event
Chargeable Event that takes place but is not recorded by the system
3.17
monitoring
process within a distributed system for collecting and storing state data
NOTE This can be used to observe metrics during operation.
3.18
overcharging
situation where the calculated charge is above the Accepted Charging Error Interval
4 © ISO 2012 – All rights reserved

3.19
Payment Claim
recurring statement referring to concluded Billing Details made available to the Toll Service Provider by the Toll
Charger who indicated and justified the amount due
NOTE The Payment Claim is used by the Toll Service Provider to issue financial objects to its customers (e.g. invoices
on behalf of the Toll Charger). A given toll Payment Claim is referring to concluded Billing Details and takes into account
any specific commercial conditions applicable to a vehicle, a fleet of vehicles, a customer of a Toll Service Provider and/or
a Toll Service Provider. A valid “Payment Claim” has to fulfil formal requirements, including security requirements, agreed
between the Toll Service Provider and the Toll Charger.
[ISO 12855:2012, definition 3.14]
3.20
performance metrics
specific calculations used to describe the charging performance of a system
NOTE These calculations are technology and schema-independent.
3.21
Relative Charging Error
ratio between the Absolute Charging Error and the actual value, i.e. Relative Charging Error = Absolute
Charging Error/Actual Value
NOTE The topic of Actual Values and how to handle them will be dealt with in the examination framework.
3.22
representative trips
trips that are of a distance larger than a defined threshold and so have to be considered by the related metrics
NOTE 1 Only trips which exceed the threshold and cover the specific types of roads of the Toll Regime have to be considered.
NOTE 2 The threshold may be defined as zero.
3.23
Service User
User
customer of a Toll Service Provider, one liable for toll, the owner of the vehicle, a fleet operator, a driver, etc.,
depending on the context
[ISO 12855:2012, definition 3.29]
3.24
successful charging
situation where the User has been correctly charged according to the rules of the system
NOTE For discrete Charging Schemes this means that for a given chargeable journey the Chargeable Events have been
correctly identified and for continuous schemes that the Charge determined is within the Accepted Charging Error Interval.
3.25
Toll Charger
legal entity charging toll for vehicles in a toll domain
NOTE In other documents the terms operator or toll operator can be used.
[ISO 17573:2010, definition 3.16]
3.26
Toll Service Provider
legal entity providing customer toll services on one or more toll domains for one or more classes of vehicle
NOTE 1 In other documents the terms “issuer” or “contract issuer” can be used.
NOTE 2 The Toll Service Provider can provide the OBE or can provide only a magnetic card or a smart card to be used
with OBE provided by a third party (just as a mobile telephone and a SIM card can be obtained from different parties).
NOTE 3 The Toll Service Provider is responsible for the operation (functioning) of the OBE with respect to tolling.
NOTE 4 Adapted from ISO 17573:2010.
3.27
Toll Declaration
statement to a Toll Charger that confirms the presence of a vehicle in a toll domain in a format agreed between
the Toll Service Provider and the Toll Charger
[ISO 12855:2012, definition 3.19]
NOTE A valid Toll Declaration has to fulfill formal requirements, including security requirements, agreed between the
Toll Service Provider and the Toll Charger.
3.28
trip
part of space-time trajectory of a particular vehicle within a Toll Regime
NOTE The exact definition of the start and end of trip is dependent on the Toll Regime and technology approach.
3.29
undercharging
situation where the calculated charge is below the Accepted Charging Error Interval
3.30
User Account
assets, liabilities, income, expenses, and equity of a Service User in his relationship to his Toll Service Provider
3.31
User Complaint
complaints related to service provision received by the Toll Service Provider from its Users via contact channels
6 © ISO 2012 – All rights reserved

4 Abbreviated terms
CCTV Closed Circuit Television
DSRC Dedicated Short-Range Communications (ISO 14906)
E2E End-to-End
EFC Electronic Fee Collection (ISO 17573)
EETS European Electronic Toll Service (ISO 17573)
FE Front End (ISO/TS 17575-1)
GNSS Global Navigation Satellite System
NOTE A generic term used for a satellite localization system such as GPS and GALILEO.
ITS Intelligent Transport Systems
OBE On-Board Equipment (ISO 17573)
OBU On-Board Unit
RSE Roadside Equipment
SLA Service Level Agreement (ISO/IEC 20000-1)
TSP Toll Service Provider (ISO 17573)
TC Toll Charger (ISO 17573)
5 Definition of charging performance metrics
5.1 General
Charging performance metrics can be applied at different levels of the processing chain from the lowest
level where the basic charging information is measured to the final computation of charging information to be
provided to Toll Chargers and Service Users.
In practice, it is worth defining metrics for the information transmitted through the established (and standardized)
interfaces, plus those that can be defined at an overall Tolling Scheme Level, so call End-to-End Metrics.
ISO/TS 17575-3
- Context data
Proxy
Toll Service Provider
ISO/TS 17575-1
(back office)
OBE - Charge Reports
ISO 14906 ISO 12855
ISO 12855
- Charging identification & - Trust objects - Trust objects
Transfer Charging information - Exception list - Toll context data
- Transit information - QA parameters - Billing details
- User identification - Address data - Payment claims
ISO/TS 12813 for enforcement
- QA parameters
- OBE interrogation
ISO/TS 13141 - Toll declarations
- RSE localisation data (GNSS)
Other proprietary Toll Charger
specific configuration data
Toll Charger
RSE
Toll declaration (DSRC, video,
(back office)
vehicle measurements .)
Figure 3 — EFC Architecture and Interfaces
In accordance with ISO 17573, and with the associated interface standards ISO/TS 17575-1 and ISO 12855,
metrics shall be based on the following charging information exchanges highlighted in bold italics in Figure 3:
— Charge Reports as transmitted from the Front End to the Service Provider’s Back End
(ISO/TS 17575-1:2012, 6.2).
— Charging identification and Transfer Charging information as exchanged between the OBE and the RSE
for DSRC systems (ISO 14906).
— Toll Declarations as transmitted from the Service Provider to the Toll Charger for autonomous systems
(ISO 12855:2012, 5.2.7).
— Billing Details as transmitted from the Toll Charger to the Service Provider (ISO 12855:2012, 5.2.8).
— Payment Claims transmitted from the Toll Charger to the Service Provider (ISO 12855:2012, 5.2.9).
NOTE 1 Payment Claims form the basis for User Statements/Invoices as transmitted in the interface between Service
Provider and the User (User Account).
Charging Metrics defined at the level of Charge Reports and Toll Declarations focus on the ability of the Service
Provider Front End and associated back-office functions to correctly detect and report Charging Events. Charging
Metrics defined at the level of Billing Details and Payment Claims focus on the Toll Charger’s ability to correctly
determine the Charges incurred by Users based on the Toll Declarations received. Charging Metrics defined
at the level of User Statements/invoices cover the overall Charging Performance for an individual User, which
include other capabilities of the complete system (communications reliability, infrastructure availability, etc.).
In addition to the metrics that can be defined at the level of interfaces, it is often common practice to define
metrics which measure the overall Charging Performance in a toll scheme, in particular for procurements of
toll schemes where the roles of Toll Charger and Service Provider are provided by a single entity; these are
defined as End-to-End Metrics in this part of ISO/TS 17444. In toll schemes where the roles of Toll Charger and
8 © ISO 2012 – All rights reserved

Service Provider are performed by different entities then the E2E metrics measure the combined performance
of the Toll Charger and Service Provider.
For the purposes of this part of ISO/TS 17444 Charging Performance metrics are defined for the six levels
below and are independently presented in 5.3 to 5.8
— End-to-End Metrics;
— User Account Metrics;
— Payment Claim Metrics;
— Billing Details Metrics;
— Toll Declaration Metrics;
— Charge Report Metrics.
NOTE 2 The Charging Metrics defined in each subclause are not intended to be mutually exclusive and the decision as
to which Charging Metrics to use is out of the scope of this part of ISO/TS 17444.
Figure 4 shows the hierarchy of Charging Metrics as defined in this part of ISO/TS 17444 and illustrates how
the discrete and continuous nature of Tolling Schemes have an impact on the metrics that can be defined for a
particular scheme under consideration.
End-to-End Charging Metrics (5.3)
User Account Charging Metrics (5.4)
Payment Claim Charging Metrics (5.5)
Billing Details Metrics (5.6)
Toll Declaration Metrics Toll Declaration Metrics
(Discrete Schemes) (Continuous Schemes)
(5.7.2 & 5.7.3) (5.7.2 & 5.7.4)
Charge Report Metrics Charge Report Metrics
(Discrete Schemes) (Continuous Schemes)
(5.8.2 & 5.8.3) (5.8.2 & 5.8.4)
Figure 4 — Charging Metrics Hierarchy
For the purposes of this part of ISO/TS 17444 it is assumed that metrics defined at a level of Billing Details or
higher are independent of whether the Tolling Scheme is continuous or discrete and it is only metrics that are
defined at the Toll Declaration or Charge Report level that are dependent on the Scheme Type.
Figure 5 presents five different examples for defining options for measuring Charging Metrics in a particular
Tolling Scheme.
1) Measures charging performance at each information interface independently from each other
(with reference to the outcome of the previous stage). This is applicable for both DSRC and
Autonomous systems.
2) Measures charging performance at each information interface between Toll Service Provider and Toll
Charger. This is most applicable to Autonomous systems.
3) Measures the charging performance of the Toll Charger at the Billing Detail and Payment Claim
levels independently from the performance of the Toll Service Provider for allocating charges to User
Accounts. This is only recommended for scenarios where the Toll Charger is responsible for the
Usage Evidence (DSRC or CCTV tolling). Otherwise, the performance cannot be attributed to a single
responsible entity.
4) Measures the charging performance of the Toll Charger at the Payment Claim level independently
from the performance of the Toll Service Provider for allocating charges to User Accounts. This is only
recommended for scenarios where the Toll Charger is responsible for the Usage Evidence (DSRC or
CCTV tolling) and where there is no aggregation of Billing Details within Payment Claims.
5) Measures the End-to-End charging performance of the whole Tolling Scheme. This measurement
represents the User’s perception. It can further be recommended if all charging functions are
performed by the same monolithic entity.
Autonomous Systems Only
Charge Toll Billing Payment User
Usage
Usage Report Declaration Details Claim Account End
Evidence
ISO12855
ISO 17575 ISO12855 ISO12855 Charge(s)
1)
Service Provider Service Provider Toll Charger Toll Charger Service Provider
Charge Report Interface Toll Declaration Billing Detail Payment Claim Charges to User Accounts
Interface Interface Interface
2)
Service Provider Toll Charger Toll Charger Service Provider
Toll Declaration Interface Billing Detail Payment Claim Charges to User Accounts
Interface Interface
3)
Toll Charger Toll Charger Service Provider
Billing Details Interface Payment Claim Charges to User Accounts
Interface
4)
Toll Charger Service Provider
Payment Claim Interface Charges to User Accounts
5)
E2E
Charges to User Accounts
Figure 5 — Charging Metrics mapping to toll scheme Implementations
The reference value for the measurement is an important issue. Each black filled circle represents the reference
value for performance evaluation for the next stage (to the right).
NOTE The actual presence of a vehicle cannot be taken as a reference for performance measurement because it
is “unknown”. For every performance metric which involves comparison to the “real world” a tangible reference (“usage
evidence”) needs to be defined: the record generated to monitor the performance (CCTV, loop detection, manual auditor
log file, Enforcement Record.) will be elaborated in ISO/TS 17444-2.
10 © ISO 2012 – All rights reserved

5.2 Metric Identification
The metric’s unique identifiers are defined in the following manner: CM-xxx-aa
Where:
1) CM signifies “charging metrics”;
NOTE This is to allow distinctions in case of expansion to other performance metrics.
2) xxx identifies the level of the metric:
— “E2E” for “End-to-End”;
— “UA” for “User Account”;
— “PC” for “Payment Claim”;
— “BD” for “Billing Details”;
— “TD” for “Toll Declaration/Charge Report”, which is also subdivided into:
— “DTD”, signifying “Toll Declaration/Charge Report” for discrete systems, and
— “CTD”, signifying “Toll Declaration/Charge Report” for continuous systems;
— “CR” for “Charge Report”, which is also subdivided into:
— “DCR”, signifying “Charge Report” for discrete systems, and
— “CCR”, signifying “Charge Report” for continuous systems;
3) aa identifies the unique number within the level.
5.3 End-to-End metrics
End-to-End Charging Performance Metrics are defined at a level which determines the overall charging
performance of a toll scheme across all interfaces on the overall system level for a group of users.
Table 3 provides details of the metrics that have been defined for End-to-End Charging Metrics.
Table 3 — End-to-End Charging Metrics
Metric ID Metric Name Description Definition
CM-E2E-1 E2E Correct Metric that measures the overall The probability that for any set of
Charging Rate probability that Users are correctly representative trips travelled by a set of
Charged by a toll scheme. Users during a time span Δt the Average
Relative Charging Error is within the
Accepted Charging Error Interval.
CM-E2E-2 E2E Overcharging Metric that measures the overall The probability that for any set of
Rate probability that Users are overcharged representative trips travelled by a set of
by a toll scheme. Users during a time span Δt the Average
Relative Charging Error is above the
Accepted Charging Error Interval.
CM- E2E-3 E2E Metric that measures the overall The probability that for any set of
Undercharging probability that Users are undercharged representative trips travelled by a set of
Rate by a toll scheme. Users during a time span Δt the Average
Relative Charging Error is below the
Accepted Charging Error Interval.
CM- E2E-4 E2E Late Metric that measures the overall level of The probability that for any set of
Charging late charging within a toll scheme, i.e. representative trips travelled by a set of
the proportion of Charges that appear Users during a time span Δt the Charge
later than the
...