Extending the Network Robustness Index to include emissions: a holistic framework for link criticality analysis for Montreal transportation system

ABSTRACT

The Network Robustness Index (NRI) was one of the first tools to successfully assess networkwide congestion effects due to single-link closures. This paper investigates the use of systemwide metrics in the context of Montreal’s urban road network, and provides a new mechanism to evaluate the importance of individual links while internalizing the environmental perspective. Specifically, the NRI is expanded to include road emissions in the link criticality analysis process, resulting in the creation of an Emissions-based NRI (ENRI), to be used in conjunction with the NRI. The results of this new Emissions-based NRI (ENRI) are compared with the NRI results and we observe that both tools provide similar results for major scenarios (such as capacity reduction on major bridges) while for minor scenarios (such as capacity reduction on arterial roads) the results are quite different. The results suggest that new holistic frameworks are needed to assess link criticality in urban areas.

KEYWORDS:

• Link criticality
• link vulnerability
• Network Robustness Index
• traffic emissions
• Montreal

Acknowledgments

The authors would like to extend their thanks to the Trottier Institute for Sustainability in Engineering and Design (TISED), which funded part of the research through their named Summer Undergraduate Research in Engineering (SURE) Award at McGill University. The financial contributions of NSERC and FQRNT were also critical, as was the help of Ehab Diab for the GIS maps. The authors would also like to acknowledge feedback from two anonymous reviewers on an earlier version of the paper.

Notes

1. The two types of roadways yield very different driver behaviors, with interrupted roadways experiencing stop-and-go traffic, whereas uninterrupted roadways are meant to be closer to free-flow conditions (Sider et al. 2013).

2. We have compared the scenarios based on volume and V/C results The results were not presented as the results from the exercise were less informative on the criticality of links in the Montreal urban network Interested readers can obtain the results from the authors.