Heterogeneity Aware Emission Macroscopic Fundamental Diagram (e-MFD)

Abstract

Transportation sector is one of the major producers of greenhouse gases which are responsible for climate change. Finding an appropriate emission estimation tool for large-scale networks is essential for developing efficient emission mitigation strategies. This paper presents an advanced version of the emission macroscopic fundamental diagram (e-MFD) which improves the stability and accuracy of the previous model. A bi-modal function is applied to separate free-flow and congested branches of the e-MFD. The accuracy of the proposed e-MFD is evaluated with both a synthetic grid network and a real-world city-level network. The study also assesses the model’s stability under directional traffic demands and road incidents. A comparison with the original e-MFD also verifies the superiority of the proposed model with higher accuracy. Standard deviation of density used in the proposed model to boost the performance. It is worth mentioning the standard deviation can be recorded with the existing hardware, such as loop detectors, and does not impose a considerable computational complexity. The proposed model can be employed for emission measurement in large-scale networks and hierarchical traffic control systems for more homogeneous congestion distribution and emission control.

Multiobjective Model Predictive Control Based on Urban and Emission Macroscopic Fundamental Diagrams

“…Again, there is a need for proper calibration of each curve, since [60], through experimental analysis, suppose congestion results in more cumulative emissions overall. This is confirmed in [62] in which the authors explored the three branches of the e-MFD already highlighted in Fig. 1.…”

“…So, the e-MFD relates aggregate traffic dynamics to emissions providing a mechanism to apply network-wide traffic control and demand management policies to emissions reduction objectives. This is confirmed in [62] in which the authors explored the three branches of the e-MFD (i.e. free flow, saturation and congested).…”

“…In this regard, in Fig. 1 the empirical e-MFD points collected by [62] are reported by highlighting the free flow, the saturation and the congested branches of the curve. The challenge of striking a balance between congestion alleviation and emission reduction is notably intricate, particularly when the network operates at level of accumulations up to the saturation regime.…”

“…Many network control strategies focus on steering the network into the saturation domain, where throughput is maximised. However, by analysing the e-MFD curve, it becomes evident that emission levels increase proportionally to the accumu-FIGURE 1: An empirical e-MFD curve, [62] lation values. Therefore, while a traffic management policy maximizes throughput, it may cause excessive emission levels.…”

“…1. Particularly, more details about the usage of the e-MFD curve to model emission monitoring systems have been provided in [62]. To conclude, it is obvious that by relating aggregate traffic dynamics to emissions, the e-MFD could provide a mechanism to link network-wide traffic control and demand management policies to emissions reduction objectives.…”