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<article xmlns:xlink="http://www.w3.org/1999/xlink">
  <front>
    <journal-meta />
    <article-meta>
      <title-group>
        <article-title>Towards Runtime Detection of Novel Trafic Situations</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>Ishan Saxena</string-name>
          <email>ishan.saxena@dlr.de</email>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Dominik Grundt</string-name>
          <email>dominik.grundt@dlr.de</email>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Eike Möhlmann</string-name>
          <email>eike.moehlmann@dlr.de</email>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Bernd Westphal</string-name>
          <email>bernd.westphal@dlr.de</email>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <aff id="aff0">
          <label>0</label>
          <institution>German Aerospace Center (DLR) e.V., Institute of Systems Engineering for Future Mobility</institution>
          ,
          <addr-line>Oldenburg</addr-line>
          ,
          <country country="DE">Germany</country>
        </aff>
      </contrib-group>
      <pub-date>
        <year>2025</year>
      </pub-date>
      <abstract>
        <p>Automated Vehicles developers need to define an Operational Design Domain (ODD) where such vehicles can operate safely. In order to extend the defined ODDs, the developers base their decision after detailed analysis of recorded data from multiple data collection drives. For the acquired data, it is important to know whether it is known trafic situation information (inside the automated vehicle's ODD) or novel information that can be used to expand the ODD. The large amount of data that is generated by a modern vehicle's sensors makes data storage and eficient analysis for expanding ODDs hardly feasible (most of the current approaches record all sensor data and then post-process the data using AI-based methods and finally perform manual checks in order to find the novel data). Hence, there is a need to classify trafic situations as novel at system runtime for an appropriately abstract notion of novelty so that the conceptually same trafic situation, e.g. on two similar days, is not considered novel only because of the diferent date. We propose a new methodology for detection of novel trafic situations at system runtime. The methodology is based on a trafic catalogue that consists of abstract trafic situation descriptions, which are a formalized representation of sets of concrete trafic situations. Continuous, automatic checks for satisfaction of the current trafic situation against the trafic catalogue provides verdicts about the novelty of the current trafic situation. Using an example, we show how domain experts can utilize the detected novelties to create such a trafic catalogue such that the novelties are classified as known in the future. The proposed method doesn't require any pre-training of an AI-based classifier and is human understandable, explainable and traceable.</p>
      </abstract>
      <kwd-group>
        <kwd>eol&gt;Novel Trafic Situation Detection</kwd>
        <kwd>Data Recording</kwd>
        <kwd>Trafic Situations</kwd>
        <kwd>Formal Specification</kwd>
        <kwd>Runtime Monitoring</kwd>
      </kwd-group>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>1. Introduction</title>
      <p>
        In the automotive domain, ensuring the safe operation of automated vehicles is a topic of great interest.
One of the ways in which Automated Driving Function (ADF) developers can ensure safe operation of
automated vehicles involves allowing such vehicles to only drive while inside their Operational Design
Domain (ODD). The ODD of an automated vehicle may be defined as the set of operating conditions,
such as environmental factors, trafic conditions, etc., for which the vehicle has been designed and
tested rigorously and has proven capable of safe operation [
        <xref ref-type="bibr" rid="ref1 ref2 ref3 ref4">1, 2, 3, 4</xref>
        ].
      </p>
      <p>
        ADF developers continuously analyse the ODD of their automated vehicles to pursue their expansion
in order to enable safe operation of such vehicles in additional operating conditions. The usual process
for expanding the ODD involves manual identification of operating conditions by experts that are
not yet covered by the ODD, carrying out training data collection drives aiming to encounter the
desired operating conditions, filtering of the collected data, training the ADFs on the filtered data and
ifnally testing whether the automated vehicle is now capable of safe operation for the new operating
conditions [
        <xref ref-type="bibr" rid="ref5">5</xref>
        ]. This process of data collection, data filtering, ADF training and testing should be
continued even after delivery to further improve the safe operation of automated vehicles.
      </p>
      <p>
        This process has certain drawbacks. Data collection is currently carried out by recording all sensor
data during the entire drive. A vehicle equipped with RADAR sensors, LiDAR sensors and cameras
generates around 5 GB of data per second [
        <xref ref-type="bibr" rid="ref6">6</xref>
        ], which requires a large amount of on-device storage.
      </p>
      <p>Ofline identification of novel operating conditions (i.e. conditions not yet present inside the ODD)
from such a large dataset is a cost-, time- and resource-intensive process. This is because the data is
available as unorganized and unlabelled collection of sensor data and recordings. This large amount of
data must be post-processed, clustered, and then manually checked by experts to determine presence of
novel operating conditions.</p>
      <p>
        In this paper, we propose a methodology for automatic identification of novel operating conditions
at system runtime. This allows targeted recording of novel sensor data during data collection. In detail,
our approach proposes the use of runtime monitoring to classify the current trafic situation based on a
trafic catalogue. The proposed trafic catalogue would consist of abstractly specified trafic situations
representing operating conditions that experts have determined to be already present in the ODD.
Concretely, we use the Spatial View (SV) formalism of the Trafic Sequence Charts (TSCs) [
        <xref ref-type="bibr" rid="ref7">7</xref>
        ] language.
SVs allow a visual yet formal specification of abstract trafic situations, especially the spatial relations
between various road users. This classification at system runtime would allow recording of only novel
data, leading to a saving of storage space, time and compute resources. We have exemplarily applied
the approach in a simulation-based environment for the first steps towards a trafic catalogue.
      </p>
      <p>
        A number of approaches are present in literature dealing with identification of novelties in the
automotive domain. For us, approaches that deal with novelties arising in a trafic situation due to
interaction of trafic participants with each other are of interest. The approaches introduced in [
        <xref ref-type="bibr" rid="ref8">8</xref>
        ]
and [
        <xref ref-type="bibr" rid="ref9">9</xref>
        ] encode their inputs using autoencoder and CLIP respectively. Finally, the encoded information
is clustered based on diferent parameters to detect novelties. The authors in [
        <xref ref-type="bibr" rid="ref10">10</xref>
        ] propose a proprietary
novelty metric called Unexpectedness Index that measures how unexpected the driving scenario is
from perspective of the system under test. They use this novelty metric for the generation of
unknownunsafe scenarios in simulation as per SOTIF [
        <xref ref-type="bibr" rid="ref11">11</xref>
        ]. These methods require embedding of data into an
AI-generated latent space for detection of novelties. Hence, they sufer from the known issues occurring
due to the black-box behaviour of AIs. Additionally, they are only suitable for ofline tasks and cannot
directly be used to detect novelties at system runtime.
      </p>
      <p>
        The research closest to this work is [
        <xref ref-type="bibr" rid="ref6">6</xref>
        ], where the authors propose a method for real-time identification
and recording of novel dynamic behaviour using single-variate time-series signal classification. The
authors propose construction of a Behaviour Forest based on continually arriving data points to discover
dynamic behaviour. Once a novel dynamic behaviour is found which has not been encoded in the
Behaviour Forest yet, the leaf nodes are extended and the corresponding time-series data is recorded.
Our proposed approach allows for detection of novelties from multidimensional sensor data, and allows
detection of novelties occurring due to interaction of multiple objects at system runtime.
      </p>
    </sec>
    <sec id="sec-2">
      <title>2. Novel Trafic Situation Detection</title>
      <p>In this section, we present our concept for novel trafic situation detection at system runtime. First,
we provide definitions for the terminology used in the concept. On the basis of these definitions, we
ifrst define a novel trafic situation. Further, we introduce a method for detection of such novel trafic
situations at vehicle runtime and recording of novel data. Finally, we present how a trafic catalogue
can be created and extended by domain experts on the basis of the recorded novel data. The concept
overview is presented in Figure 1.</p>
      <p>A trafic situation consists of trafic environment and trafic participants. A trafic environment is
defined as the context in which trafic participants operate, e.g. roads, lanes, etc. A trafic participant is
an entity that interacts with trafic environment according to a set of behavioural and physical rules
and contains attributes, e.g. vehicles, pedestrians, etc. We use an Object Model  to model trafic
participants and trafic environment. Let  = (,  ,  ,  ), where  is a set of classes,  is a
set of basic types,   is a set of typed predicate symbols and   is a set of typed function symbols.
() is a finite set of typed attributes for each object class. A concrete trafic situation is a spatial
arrangement of trafic participants, at a particular point of time, within the trafic environment along
with their state. Concrete trafic situations, over the Object Model  , are defined as a function 
over a finite set of object identities ID (pertaining to the objects present in the situation) along with a
type-consistent valuation of their attributes.  : ID ↛ (() ↛ ), where ID is the set of object
identities provided to class instances,  is the domain set of attribute types. Hence,  ()( : ) ∈ ().</p>
      <p>
        Trafic situation specifications formally describe desired state and spatial properties of concrete trafic
situations. They are defined as a set of well-typed predicate logic formulae over  . Examples of
trafic situation specification include Spatial Views [
        <xref ref-type="bibr" rid="ref7">7</xref>
        ], Abstract Scene Graphs [
        <xref ref-type="bibr" rid="ref12">12</xref>
        ], etc. Let  represent
the valuation of variables present in predicates derived from the attribute values of a specific concrete
trafic situation. We define that this specific concrete trafic situation  will satisfy a trafic situation
specification , i.e.  ⊨  ⇐⇒  ⊨  (), where  () are predicates present in specification . Let Σ
represent a set of all concrete trafic situations that can exist, then the specific concrete trafic situations
that are specified by the specification  can be represented as Σ ⊆ Σ. It is possible for a concrete trafic
situation to satisfy more than one trafic situation specifications. Finally, a trafic catalogue is a finite
set of trafic situation specifications. For the case of Novelty Detection, we assume that the concrete
trafic situations represented by the specifications have already been seen by the domain experts and
are no longer of interest for data recording. A trafic catalogue is represented as   = (1, 2, . . . ),
where  is the number of trafic situation specifications present in the catalogue.
      </p>
      <p>
        We define a novelty or a novel trafic situation as a concrete trafic situation which satisfies none of
the trafic situation specifications present in a trafic catalogue. Formally, if ∀ ∈   :  N ⊭ , then
 N is a novelty. We define novel data as the sensor values contained in the concrete trafic situation
which satisfies none of the formalized situations present in a trafic catalogue. This is the data that
should be recorded and is of interest to domain experts. For detection of novelties at system runtime,
we require a method that can provide us continuous verdicts about whether a concrete trafic situation
satisfies any of the trafic situation specifications present in a trafic catalogue. Such trafic situation
specifications, occurring in the automotive domain, are usually quite complex. The complexity arises
from the need to specify interactions between multiple trafic participants, the trafic environment
and their attributes. In the field of Scenario-based Testing [
        <xref ref-type="bibr" rid="ref13">13</xref>
        ], Runtime Monitoring (RM) has already
been used for continuous checking of complex system requirements for system runs in the automotive
domain [14]. These complex system requirements are specified using abstract scenario specifications
and concrete system runs are monitored for satisfaction against them. We also require a similar check
for trafic situations, and since a scenario consists of finitely-many trafic situations, we conclude that
we can use RM similarly for our purpose. RM for a concrete trafic situation is performed using runtime
monitors which are software components that continuously take as input (processed) sensor signals and
provide an immediate verdict regarding satisfaction with a trafic situation specification. We generalize
the runtime monitoring definition for a complete trafic catalogue as follows:
      </p>
      <p>Mon(,   ) :=
{︃
⊤
⊥
if ∃ ∈   :  ⊨ ,
otherwise
(1)
When Mon(,   ) = ⊤, this implies that the current concrete trafic situation is an already known
situation and satisfies at least one of the trafic situation specifications present in the trafic catalogue.
When a novelty is encountered i.e. Mon(,   ) = ⊥, then the data recording mechanism is triggered
to record the corresponding sensor data. The recording of data should be continued till the next
Mon(,   ) = ⊤ verdict is received.</p>
      <p>Once the novel data recordings are available to the domain experts, they are able to analyse and
recognize the trafic situations occurring in the recordings. Formalization of a subset of the identified
trafic situations into specifications allows them to discuss and decide, by including them in the trafic
catalogue, for which set of trafic situations suficient data is present and hence should be filtered out
during future data recording.</p>
    </sec>
    <sec id="sec-3">
      <title>3. Application Example: A Catalogue of 2-Lane Highway Situations</title>
      <p>In this example, we assume that the domain experts want to start from scratch and intend to build
their trafic catalogue along the way. Their Data Collection Vehicle (DCV) starts collecting data while
driving on a two-lane highway. Since initially, there are no situation specifications present in the trafic
catalogue (  = ∅), hence all data is collected as novel data. After the first day of data collection, the
domain experts check the collected data and identify certain trafic situations and decide to include
them as trafic situation specifications in the trafic catalogue.</p>
      <p>
        For creation of our example trafic catalogue, we use the Spatial View (SV) formalism from the Trafic
Sequence Charts (TSCs) [
        <xref ref-type="bibr" rid="ref7">7</xref>
        ] specification language. SVs enable the specification of spatial relations
between trafic participants and trafic environment, as well as the constraining of attributes, such as the
distance between objects or the acceleration of an object. The semantics of a SV is a logical formula over
the object model  and respective attributes specified. The SVs shown in Figure 2 contain four object
symbols that are assigned to objects in the object model  (see Table 1). We assume the following
assignment with (symbol, unique object identity, Class): (blue car, , Car), (green car, ℎ, Car),
(right lane, , Lane), and (left lane, , Lane). Furthermore, nowhere-boxes (light grey boxes with red
borders and dashed crosses) are used, which prohibit the existence of the class specified therein. In the
case of Figure 2b,  is located on the right lane, and no other object instance of the class Car should
be located behind or in front of , nor on the left lane. In this example, the nowhere-boxes present in
the Spatial Views have been mapped to the  attribute of . This attribute returns a list of
objects which are present in the range of , which can be used to evaluate the logical sub-formula
related to nowhere-boxes. Hence, the logical formula derived from the SV in Figure 2b is:
2
      </p>
      <p>= .. &gt; . ∧ .. &lt; . ∧ . = ∅Car
where  is an abbreviation for the projection of the positional anchor to its second component.</p>
      <p>The three trafic situation specifications identified by the domain experts and specified as Spatial
Views are added to the trafic catalogue   = {1, 2, 3}. The corresponding SVs are presented in
d&lt;100[m]
(a) 1: Ego vehicle on the left lane
of a two-lane highway
(b) 2: Ego vehicle on the right
lane of a two-lane highway
(c) 3: Ego vehicle with other
vehicle on left lane at a distance
of at least 50 m behind it</p>
    </sec>
    <sec id="sec-4">
      <title>4. Conclusion and Future Work</title>
      <p>We have presented a methodology to detect novel trafic situations based on a trafic catalogue that
consists of formally specified known trafic situations. This method is useful for developers of Automated
Driving Function (ADF) who want to ensure safe operation of their vehicles by only allowing them to
operate within their Operational Design Domain (ODD). The method enables a structured construction
of the ODD by recording sensor data only when the operating conditions of the vehicle do not correspond
to those present in the trafic catalogue. The lack of AI-based components in our approach makes
it explainable, traceable, and understandable to humans. We showed how to apply the concept for
creating a trafic catalogue by domain experts on the example of 2-lane highway situations.</p>
      <p>Future work is to test the approach rigorously on larger simulation and real world datasets (similar
to [24], where runtime monitoring using TSCs is demonstrated for a research vessel), and to implement
the monitors on automotive-grade hardware. Further eforts are needed to extend the methodology to
detect novel trafic scenarios (i.e., sequences of situations), for tool-support for completeness
argumentations for the catalogue, and for adapting the technique for use in other transportation domains such
as maritime.</p>
      <p>(a) DCV simulation run with empty trafic catalogue
(b) DCV simulation run with extended trafic catalogue</p>
      <p>Figure 3: Simulation results from the prototypical implementation of our proposed concept</p>
    </sec>
    <sec id="sec-5">
      <title>Acknowledgments</title>
      <p>The research leading to these results is funded by the German Federal Ministry of Education and
Research under grant agreement No 16MEE044 (EdgeAI-Trust) and by the Chips Joint Undertaking
under grant agreement No. 101139892 (EdgeAI-Trust).</p>
    </sec>
    <sec id="sec-6">
      <title>Declaration on Generative AI</title>
      <p>During the preparation of this work, the author(s) used LanguageTool in order to: Grammar and spelling
check. After using these tool(s)/service(s), the author(s) reviewed and edited the content as needed and
take(s) full responsibility for the publication’s content.
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DEvelopment (ASYDE), Berlin, Germany, 26th and 27th of September 2022, volume 371 of Electronic
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    </sec>
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