IEEE Circuits and Systems Magazine - Q4 2019 - 63

is still needed in developing application-oriented network
analysis so that results produced from network theory can
be readily translated to useful practical information and
more desirably at the operational level.
Robustness analysis is another important area. Evaluating the resilience of PTNs improves understanding of
various criteria of network breakdown under different attack strategies. Future research topics may also include
the study of the passenger migration process, the application of integrated multiple transport modal analysis to analyze real-world complexity of passenger route
selection, effects of polarization of stops and routes on
the demand flow in the network, etc. Furthermore, while
research efforts have been devoted to the spatial dynamics of PTNs in the past, the temporal dynamics reflecting
the topological variation of a PTN at different times of
the day should deserve serious attention. Another major area of research is dealing with the integration of the
multiple transport networks to form a coordinated and
complimentary transport system that can significantly
enhance the traffic carrying capacity and efficiency of
the entire system. In the past, very little contribution has
been made through multi-layer analysis where individual transport networks are treated as independent topologies, and understanding the interaction among these layers should deserve more research attention in view of
the practical relevance of integrated PTNs.
Finally, we would like to emphasize that applying graph
theory to the analysis of public transport behavior offers
an effective and convenient way to understand the network operation at both the local and global levels. The
various spaces of network representation provide the fundamental network representation framework for analyzing
PTNs. The incorporation of practical network parameters
and the emphasis of the dynamic spatio-temporal behavior of the network can offer a broader and more practical
view of the network functionality relevant to the network
operators. Alongside with offering these advantages, the
network-based analysis also raises a few technical challenges as a consequence of increased computational time
with increasing network size and the lack of real-world
datasets. In closing, we believe that PTN analysis from a
graph theory perspective will continue to uncover important network properties and to serve as a solid foundation
on which to develop performance optimization strategies, network planning, service deployment, maintenance
schedules, etc. for achieving better and more sustainable
transport services and eventually smarter cities.
Acknowledgment
We would like to thank Prof. John W. Polak of Imperial
College London for his insightful suggestions in organizing this survey, and for shedding light on the areas of
FOURTH QUARTER 2019

future work. We also thank Xingtang Wu of Beijing Jiaotong University for his contribution towards sharing
information on metro network analysis. This work was
supported in part by the National Natural Science Foundation of China (Project 61401384) and the Hong Kong
Polytechnic University (Project 4-BCCH).
Tanuja Shanmukhappa received the B.E.
degree in Electronics and Communication Engineering from the Kuvempu University in 2010, and the M.Tech. degree
in Telecommunication Engineering from
Visveswaraya Technological University
(VTU) in 2013. She was awarded with the Ph.D. degree in
Electronic and Information Engineering from the Hong
Kong Polytechnic University, Hong Kong, in 2019. She
was the recipient of university gold medal in her master's degree in 2013. Tanuja completed her exchange program at Imperial College London, UK, in 2018. Her current research interests include graph theory and network
science, transportation network analysis, and vehicular
ad-hoc networks (VANET). Tanuja also had industry experience working as an intern and trainee at Infineon
Technologies and NXP semiconductors, India, respectively. She is a student member of IEEE.
Ivan Wang-Hei Ho (M'10-SM'18) received
the B.Eng. and M.Phil. degrees in information engineering from The Chinese
University of Hong Kong, Hong Kong,
in 2004 and 2006, respectively, and the
Ph.D. degree in electrical and electronic
engineering from the Imperial College London, London,
UK, in 2010. He was a research intern with the IBM Thomas J. Watson Research Center, Hawthorne, NY, USA, and
a Postdoctoral Research Associate with the System Engineering Initiative, Imperial College London. In 2010, he
co-founded P2 Mobile Technologies Ltd, where he served
as the Chief Research and Development Engineer. He is
currently an Assistant Professor with the Department of
Electronic and Information Engineering, The Hong Kong
Polytechnic University, Hong Kong. His research interests include wireless communications and networking,
specifically in vehicular networks, intelligent transportation systems, the Internet of Things, and complex network analysis of transportation and communication networks. He primarily invented the MeshRanger series
wireless mesh embedded system, which received the
Silver Award in Best Ubiquitous Networking at the Hong
Kong ICT Awards 2012. He is currently an Associate Editor of the IEEE Access and the IEEE Transactions on Circuits and Systems II, and served as the TPC Co-Chair
of the CoWPER Workshop in conjunction with IEEE
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