The importance of interactions in determining service measures for bicycles

Osowski, Chris and Waterson, Ben (2014) The importance of interactions in determining service measures for bicycles. 46th Annual Conference of the Universities’ Transport Study Group, Newcastle upon Tyne, United Kingdom. 06 - 08 Jan 2014.

Abstract

The lack of agreed and objective measures for cycle service quality and capacity is an increasing barrier to the development of high-quality infrastructure. High cycle mode share jurisdictions face issues relating to increased cycle congestion whilst simultaneously, low cycle mode share jurisdictions face increasing calls for investment in cycle infrastructure, yet the ability to economically evaluate proposals is lacking. In both circumstances, a lack of robust quantitative measures is an issue. The limited existing measures for cycle service quality are developed based on the “isolated cyclist” or on a general assumption of non-impedance. By contrast, the fundamental principles of highway traffic flow (and of pedestrian flow) are entirely predicated on the concept of the constituent interactions, with speed-flow/density-flow curves being a well-established and empirically verified result of this.
Consequently, to assess the importance of interactions between cyclists in service quality and capacity measures for bicycles, an agent-based 2D microsimulation and social-force model was developed to test the validity of the non-impedance assumptions for unidirectional flow. The ability of the bicycles to interact and change speed resulted in both qualitative and quantitatively different outcomes to non-interaction. The speed-changing interactions led to outcomes more in keeping with empirical data and experience; and with service quality degrading rapidly as capacity is approached in comparison to non-speed-changing behaviour where service quality changes relatively slowly. The results from the simulation model therefore bring into question the validity of analysis that relies on isolated cyclists or non-interaction for use in quantitative measures. In particular, the non-linear increasing sensitivity of the quality of service as flow rates increase demonstrates the need to properly consider the interaction of the constituent bicycles in any realistic quantitative measure.

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Contributors

Author: Ben Waterson

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