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  <front>
    <journal-meta />
    <article-meta>
      <title-group>
        <article-title>Decision-making in Urban Trajectories of Bike Users: a Preliminary Study</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>Merlin Raud</string-name>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Amnir Hadachi</string-name>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Rajesh Sharma</string-name>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Flavio Bertini</string-name>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <aff id="aff0">
          <label>0</label>
          <institution>Department of Mathematical, Physical and Computer Sciences, University of Parma, Parco Area delle Scienze 53/A 43124 Parma</institution>
          ,
          <country country="IT">Italy</country>
        </aff>
        <aff id="aff1">
          <label>1</label>
          <institution>Institute of Computer Science, University of Tartu</institution>
          ,
          <addr-line>Narva mnt 18, 51009 Tartu</addr-line>
          ,
          <country country="EE">Estonia</country>
        </aff>
      </contrib-group>
      <abstract>
        <p>Developed countries have invested considerable eforts in promoting sustainable transportation modes, identifying bicycle use as a more environmentally friendly alternative. Nevertheless, this transition necessitates a deeper understanding of bicycle user behaviour to facilitate the process. This study investigates bike users' route selection behaviour based on real-world data. Data collected over six months from Bologna, Italy, were analysed to understand the flow and choices of bike users in a medium-small historical city. We employed a tessellation algorithm combined with Open Street Map street tags to examine bike users' preferences regarding urban trajectories. The dataset comprises of 290,117 unique trips consisting of 60,414,481 Global Positioning System (GPS) points. The results indicate that bicycles are predominantly used for short- to medium-distance trips. Specifically, in suburban regions, bike users tend to use larger roads leading to the city centre, whereas, in the city centre, they prefer routes that bypass the narrow streets of the historic area. These findings ofer insights into route choice factors and can guide improvements to cycling infrastructure for a safer, more eficient urban environment.</p>
      </abstract>
      <kwd-group>
        <kwd>eol&gt;Mobility data analysis</kwd>
        <kwd>cycling mobility</kwd>
        <kwd>urban mobility</kwd>
        <kwd>real-world data mining</kwd>
      </kwd-group>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>1. Introduction</title>
      <p>
        In response to climate change, energy crises, fossil fuel
depletion, overpopulation, and trafic congestion, sustainable
living has garnered increased attention. In densely
populated urban areas, promoting sustainable transportation is
vital. Encouraging cycling can reduce the use of motorised
vehicles and decrease trafic volumes. Cycling is a
sustainable, healthy, and economical transport mode, particularly
suitable for short-distance trips in historic and narrow urban
spaces. Facilitating bicycle use for commuting and leisure
as a sustainable transport option requires a thorough
understanding of urban mobility and travel behaviour. The role of
data mining in mobility research and urban cycling studies is
crucial. To assist in this cause, mobility studies can uncover
patterns in daily and routine human movements [
        <xref ref-type="bibr" rid="ref1">1</xref>
        ]. This
data is vital for urban planning, the development of
transportation models, and the promotion of healthy lifestyles
[
        <xref ref-type="bibr" rid="ref2">2</xref>
        ], and it supports trafic managers and policymakers in
making targeted decisions at various levels [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ]. A key
research area is bike users’ route choice behaviour. Analysing
the factors that influence bike users’ route selection can
lead to improvements in the transport network, thereby
encouraging urban cycling. The recent increase in mobile
phone records, GPS data, and other datasets have facilitated
more accurate human mobility analyses [
        <xref ref-type="bibr" rid="ref4">4</xref>
        ]. Particularly,
the use of data mining methods on GPS data provides
essential information on the movement patterns and behaviours
of bike users.
      </p>
      <p>Although various models for analysing bike users’
behaviour have been proposed, a detailed investigation of
route selection between two locations and multiple
alternative trajectories is still lacking. Moreover, despite the
precision ofered by GPS data, it is crucial to preserve users’
privacy. This paper addresses this gap by utilising
mobility data from the Bella Mossa initiative, provided by the
Public Transport Authority SRM Reti e Mobilità Srl, and the
Open Street Map (OSM) data to examine cycling patterns
in Bologna, a historic university city with narrow streets
in northern Italy. We conducted an analysis of bicycle
usage based on 290,117 self-reported unique trips, consisting
of 60,414,481 GPS points, spanning six months, from April
2017 to September 2017. Specifically, we applied
tessellation and clustering techniques to analyse mobility flows in
urban areas based on origin-destination tiles and to study
the trajectory selections of bike users.</p>
      <p>This study aims to investigate how cycling
infrastructure influences bike users’ route choices by utilising OSM
street-type tags while preserving users’ privacy. To achieve
this, the exact routes from GPS tracks are transformed into
coarser shifts between origin and destination, retaining
useful information for analysis. The following are the
highlights of this study. Firstly, we investigate the utilisation of
various types of infrastructure, including urban highways,
diferent bike lane configurations, and streets, to understand
bike users’ preferences regarding route choice. Secondly,
we identify the most frequently used flows and routes for
transportation purposes in Bologna, shedding light on
preferred routes. Lastly, we examine how road types and their
characteristics influence bike users’ route choices, providing
insights into the factors influencing route selection.</p>
      <p>The obtained results reveal that cyclists tend to favour
streets with lower trafic volumes and dedicated cycling
infrastructure. Furthermore, cyclists prefer to avoid narrow
streets in the old town when possible. Understanding these
patterns helps identify opportunities to improve
infrastructure and create a safer urban environment. For instance,
identifying the most frequently used origin-destination tiles
and the preferred paths between them can help guide
infrastructure development and promotion. Also, the findings
will guide recommendations to promote cycling as a viable
urban transportation option, and the proposed approach,
despite the conclusions being specific for the dataset, the
pipeline can be applied in similar urban contexts.</p>
    </sec>
    <sec id="sec-2">
      <title>2. Related Work</title>
      <p>
        Cycling ofers a sustainable, eco-friendly, cost-efective, and
inclusive solution for urban mobility [
        <xref ref-type="bibr" rid="ref5">5</xref>
        ]. Compact cities
support active transport but face challenges in designing
eficient cycling infrastructure due to space constraints [
        <xref ref-type="bibr" rid="ref6">6</xref>
        ].
Urban areas have diverse infrastructure for diferent users,
with dedicated bike lanes significantly promoting bicycle
use [
        <xref ref-type="bibr" rid="ref7">7</xref>
        ].
      </p>
      <p>
        The pervasive collection of tracking data has enabled
extensive trajectory data collection for applications like
intelligent transport systems, urban management, and
environmental protection [
        <xref ref-type="bibr" rid="ref8">8</xref>
        ]. However, challenges persist due to
privacy issues, commercial concerns, and data inaccuracies
[
        <xref ref-type="bibr" rid="ref9">9</xref>
        ]. GPS trajectory analysis then categorises trajectories or
uses data mining to uncover movement patterns and predict
future behaviours [
        <xref ref-type="bibr" rid="ref10">10</xref>
        ].
      </p>
      <p>
        Trajectory analysis is essential for understanding route
selection in urban environments. This process involves
choosing a specific path from an origin to a destination based
on various characteristics [
        <xref ref-type="bibr" rid="ref11">11</xref>
        ]. A deeper insight into route
choice can enhance the comprehension of infrastructure
usage and facilitate the cycling mobility promotion [
        <xref ref-type="bibr" rid="ref12">12</xref>
        ].
      </p>
      <p>In this paper, we propose a method based on tessellation
and flow analysis algorithms to study the decision-making
process of urban bike users. Specifically, we leveraged
information from OSM and addressed privacy concerns related
to the use of GPS data through a clustering algorithm.</p>
    </sec>
    <sec id="sec-3">
      <title>3. The Bella Mossa Dataset</title>
      <p>The Bella Mossa1 data was collected from the municipal
area of Bologna, a historical city in northern Italy. The
Bella Mossa initiative was a 6-month program to promote a
healthy lifestyle and sustainable mobility from 01/04/2017
to 30/09/2017. Around 15,000 unique participants recorded
895,000 trips for a total of 3.7 million travelled kilometres.
Participants earned redeemable points for cycling, walking,
and using public transport by using a GPS-enabled
smartphone app that recorded trips and anonymously sent the
data to a database. Each dataset entry includes a unique
activity ID, a user-selected activity type descriptor, and
details about the timestamp, GPS position, and accuracy. The
activity ID enables trip reconstruction without being
traceable to the participant. In this study, we specifically focus
on data points labelled as cycling activities. The dataset is
anonymised; individual user data has not been analysed,
and only aggregated analysis results are presented.</p>
      <p>We conducted pre-processing to clean and correct data,
addressing incomplete or inaccurate values. Preliminary
analysis identified extremely short or long activities. Short
activities with fewer than two GPS points were removed.
Long activities with pauses longer than six minutes or
where the bike user stayed in one place for over six
minutes were split into multiple segments. Activities longer
than two hours or over 30km after segmenting were
excluded, as they likely included multiple segments or
nonurban activities (e.g., sports). Activities under 100m or less
than three minutes were also removed. Finally, activities
with GPS points outside Bologna or timestamps outside the
study period were excluded. The initial dataset of 320,109
unique activities with 72,396,179 GPS points was reduced
1Due to Italian legislation restrictions, we are unable to publicly release
the datasets. Any requests can be submitted to SRM Reti e Mobilità Srl.
to 290,117 unique activities consisting of 60,414,481 GPS
points, recorded every 3-10 seconds.</p>
    </sec>
    <sec id="sec-4">
      <title>4. The Proposed Method</title>
      <p>In this section, we outline the proposed method using the
Bella Mossa dataset and the OSM street network data. First,
we employed a map-matching algorithm to refine the bike
users’ trajectories, converting sequences of GPS points into
sequences of road segments. Next, we applied tessellation
and clustering algorithms for trajectory and road type
analysis, while preserving users’ privacy.</p>
      <p>
        The map-matching algorithm assigns original GPS
coordinates to the most plausible road network segments,
improving the accuracy of GPS data and linking these coordinates
to the corresponding road network information. In practice,
we used the Open-Source Routing Machine (OSRM) project
and the Hidden Markov Model (HMM) approach with the
Viterbi path-finding algorithm [
        <xref ref-type="bibr" rid="ref13">13</xref>
        ]. This makes it possible
to check all combinations of nodes and transitions (i.e.,
intersections and road segments) to determine the optimal route
between two origin-destination GPS points, representing
it through road segments (Figure 1). Furthermore, we took
into account the time intervals between consecutive GPS
points and the typical speed of the transportation mode to
ascertain the most eficient route. The algorithm also
eliminates outliers that cannot be matched and divides traces
when there are substantial gaps in timestamps indicating
unlikely transitions [
        <xref ref-type="bibr" rid="ref14">14</xref>
        ]. The OSM street network data -a
directed graph where edges refer to road segments and nodes
refer to intersections- was acquired from Geofabrik, with a
timestamp set to January 1st, 2018. To handle anomalous
behaviours, such as bike users travelling in the opposite
direction on one-way streets, we added reversed edges to
facilitate the map-matching algorithm. The resulting road
network consists of 106,552 edges with a total length of
3,545.12km.
      </p>
      <p>
        We used a spatial tessellation algorithm to subdivide the
city area into tiles according to the GPS points densities
[
        <xref ref-type="bibr" rid="ref15">15</xref>
        ]. In particular, we first applied the K-means algorithm
using the origin GPS points of the bike user’s trajectories.
Then the identified clusters’ centre was used to create the
Voronoi diagrams (i.e., the tessellation) using the Tesspy
library. Experimentally, the ultimate -value chosen was 300.
A lower -value produces larger tiles, particularly in
suburban areas, where distinct trajectories might erroneously be
deemed similar. Conversely, a higher -value yields clusters
with too few trajectories for meaningful analysis. A
tessellation incorporating both origin and destination points was
evaluated but did not produce a significant alteration in the
resulting tile topology. This irregular tessellation method
using the clusters’ centre as points of interest (POI) to drive
the subdivision of areas results in more realistic tiles
compared to regular tessellation [
        <xref ref-type="bibr" rid="ref15">15</xref>
        ].
      </p>
      <p>Combining the representation of users’ trips with road
segments –coarser than GPS points– and map tessellation –
which identifies areas rather than precise points– makes it
possible to protect users’ privacy. Moreover, as shown in
Figure 2, the irregular tessellation enables a more focused
analysis of the city’s most frequently used areas by
increasing the density of the tiles.</p>
      <p>Flow analysis was utilised to explore the decision-making
process of bike users regarding urban trajectories. We
examined cyclists’ trajectories from an origin Voronoi tile to a
designated destination one, with the origin and destination
tiles determined using the initial and final GPS points. This
approach resulted in a comprehensive table summarising
all movements between all Voronoi tile pairs. Then detailed
trajectory analysis was conducted on the top twenty most
frequent flows, merging flows from opposite directions to
simplify distance calculation and grouping.</p>
      <p>
        Given the complexity of the road network, multiple routes
exist between origin-destination pairs. To identify the most
common paths, we performed a trajectory clustering
analysis using the Fréchet distance [
        <xref ref-type="bibr" rid="ref16">16</xref>
        ] as the clustering metric
and Density-based Spatial Clustering of Applications with
Noise (DBSCAN) as the clustering method. The Fréchet
distance, which measures the similarity between two curves,
can be intuitively explained using the analogy of a
person walking a dog on a leash: both move independently
along their respective paths from start to finish, adjusting
their speeds but without retracing their steps. Formally, the
Fréchet distance   (, ) represents the minimum leash
length required for the two to complete their paths
simultaneously and can be formalised as follows
  (, ) =  ∈ (,  ())
(1)
where A and B are the two curves, () denotes the
Euclidean distance, and  () is a continuous bijective mapping
from points on curve A to points on curve B. DBSCAN,
a widely used density-based method, was chosen for its
ability to determine the number of clusters autonomously,
handle clusters with varying densities, and identify outliers
as noise, making it particularly suitable for analyzing urban
travel patterns.
      </p>
      <p>The clustering process divided all trajectories within a flow
into distinct clusters based on the routes taken, with
cluster sizes ranging from 1 to over 200 trajectories. Clusters
containing fewer than 5 trajectories were deemed less
significant for the final analysis. Finally, leveraging the OSM
street tags, the road type analysis allows us to explore the
road infrastructure primarily used by cyclists. For
computational eficiency, the road type analysis focused on data for
the month of April, while the entire dataset was utilised for
lfow analysis. We specifically computed the road type usage
proportion by dividing the lengths of all road types in the
activity by the total activity length. Similarly, we extended
the road type analysis to the trajectory clusters to ascertain
whether street type influences bike users’ route selection.</p>
    </sec>
    <sec id="sec-5">
      <title>5. Experimental Result</title>
      <p>In this section, we briefly present the results discussing the
main outcome of the route choices and road type analysis.</p>
      <p>Highlight 1: Road Network Usage - Figure 1 depicts
the result of the map-matching process. Notably, the
cleaning procedure enables the extraction of noise-free
trajectories represented as sequences of road segments. This
preprocessing activity is of the utmost importance to
reifne subsequent analyses and obtain meaningful results. In
particular, the origin GPS points of the cleaned trajectories
were used to tessellate the city area into tiles according to
the GPS points densities. The resulting irregular tessellation
with Voronoi diagrams is shown in Figure 2. The tiles with
the highest number of activity GPS points were located in
the city centre.</p>
      <p>Highlight 2: Frequent Flows - Flow analysis utilised
tessellation tiles, assigning each activity an origin and
destination tile. Activities with the same origin-destination pair
were grouped and counted as one flow. We performed
trajectory analysis on the 20 most frequent flows, employing
trajectory clustering to identify diferent routes between
locations. Figure 3 shows the most popular routes among
the 20 top flows.</p>
      <p>Highlight 3: Route Choices - Each flow was analysed
to identify various routes between tile pairs. Trajectories
were clustered into similar route groups using the DBSCAN
algorithm, and a street-type analysis was conducted –based
on the OSM road type labels– to assess its influence on route
selection. For instance, Figure 4a illustrates the diferent</p>
    </sec>
    <sec id="sec-6">
      <title>6. Conclusion</title>
      <p>Due to environmental concerns and urbanisation, there has
been a growing emphasis on alternative modes of
transportation, such as cycling. This paper presents a framework
for analysing mobility flows within urban settings,
examining the route choices between pairs of origin-destination
tiles. An in-depth analysis of the top 20 flows showed that
route choices were notably afected by one-way streets.
According to the OSM road type labels and the results, cyclists
typically avoid travelling against the designated direction,
even when permitted. Furthermore, streets with cycling
infrastructure are preferred, while narrow ones are generally
avoided.</p>
      <p>For future work, we plan to compare the real trajectories
with potential shortest and quasi-shortest paths to better
understand why cyclists choose specific routes. Additionally,
we intend to investigate whether the efectiveness of the
clustering algorithm may impact the final inference. Also,
we plan to investigate the generalisability of the proposed
framework to other transportation modes, exploring
diferent tessellation strategies or clustering techniques to extract
the sub-network of each mode.</p>
    </sec>
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