Evaluation of the extreme traffic load effects on the Forth Road Bridge using image analysis of traffic data

E. Alexandra Micu*, Abdollah Malekjafarian, Eugene J. OBrien, Michael Quilligan, Ross McKinstray, Ewan Angus, Myra Lydon, F. Necati Catbas

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

5 Citations (Scopus)
34 Downloads (Pure)


This paper proposes a novel technique to estimate site-specific characteristic maximum traffic load effects on the Forth Road suspension Bridge (FRB). Congestion represents a critical loading state for long-span bridges and congested traffic data such as car/truck mix, vehicle weights and inter-vehicle gaps are not generally simultaneously available. Most Weigh-in-Motion (WIM) systems used worldwide to collect traffic data are not reliable in congested conditions. A closed-circuit television camera and image processing techniques were used here to collect five months of bridge traffic data on the FRB. Frames extracted from videos are automatically analysed by applying standard image processing algorithms. Hence vehicle lengths and relative positions on the bridge are extracted. An on-site WIM database with free-flowing traffic data is used to establish a statistical correlation between vehicle lengths and their weights. This correlation is applied to infer weights from the vehicle lengths recorded on the bridge. Congestion is modelled for northbound traffic by collapsing the inter-vehicle gaps to minimum values. The axial force in the main cable of the bridge is calculated using the corresponding influence line. The characteristic maximum values for axial force are evaluated for 75-year and 1000-year return periods.

Original languageEnglish
Article number102711
JournalAdvances in Engineering Software
Early online date18 Sep 2019
Publication statusPublished - Nov 2019

Bibliographical note

Funding Information:
The authors would like to acknowledge the support received from Science Foundation Ireland under US/Ireland Programme Grant 14/US/I3033 . Transport Scotland is also gratefully acknowledged. The authors would also like to thank Ms. Shruthi Ramprakash for her assistance with the data analysis.

Publisher Copyright:
© 2019 Elsevier Ltd

Copyright 2019 Elsevier B.V., All rights reserved.


  • Bridge
  • Congestion
  • Forth Road Bridge
  • Image data
  • Influence lines
  • Long-span
  • Site-specific
  • Traffic loading
  • Vehicle length

ASJC Scopus subject areas

  • Software
  • Engineering(all)

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