TY - JOUR
T1 - FitFun
T2 - A modelling framework for successfully capturing the functional form and noise of observed traffic flow–density–speed relationships
AU - Bramich, D. M.
AU - Menéndez, Mónica
AU - Ambühl, Lukas
N1 - Funding Information:
This work was partially supported by the NYUAD Center for Interacting Urban Networks (CITIES) , funded by Tamkeen under the NYUAD Research Institute Award CG001 . The High Performance Computing resources at New York University Abu Dhabi were used to perform the model fits to the EFD data. D.M. Bramich dedicates this work to Chris Gibbs, Steve Stretton, and Craige Bevil as the closest of friends who have always been there throughout the best and worst of times.
Publisher Copyright:
© 2023 The Author(s)
PY - 2023/6
Y1 - 2023/6
N2 - Measurements of the average properties of vehicular traffic are inherently noisy. The distributions of flow and speed measurements at any particular density are non-Gaussian with density-dependent variance, skewness, and kurtosis. Previous studies have failed to properly account for these complicated noise properties. In remediation, we present FitFun, a general framework for modelling any observed flow–density–speed relationship. Models specified within FitFun incorporate components for both the functional form and the noise. We define three flexible noise model components and we fit 200 different models to a high-quality sample of 10,150 observed urban flow-occupancy relationships. We compare the fits using information criteria and assess fit quality through analysis of the residuals. We find that the non-parametric Sun model for the functional form component combined with a Skew Exponential Power Type III noise component significantly outperforms all of the other models. Interestingly, we find that the city, country, road topology, and detector location have virtually no impact on model performance and fit quality, which is very convenient for model selection. The only factor of relevance from those that we studied is the effective occupancy coverage of the data. We conclude that certain models specified judiciously within FitFun can successfully capture the functional form and noise of observed flow–density–speed relationships without the need to discard data taken during non-stationary conditions. This is particularly advantageous for urban data where stationary traffic conditions are rarely observed.
AB - Measurements of the average properties of vehicular traffic are inherently noisy. The distributions of flow and speed measurements at any particular density are non-Gaussian with density-dependent variance, skewness, and kurtosis. Previous studies have failed to properly account for these complicated noise properties. In remediation, we present FitFun, a general framework for modelling any observed flow–density–speed relationship. Models specified within FitFun incorporate components for both the functional form and the noise. We define three flexible noise model components and we fit 200 different models to a high-quality sample of 10,150 observed urban flow-occupancy relationships. We compare the fits using information criteria and assess fit quality through analysis of the residuals. We find that the non-parametric Sun model for the functional form component combined with a Skew Exponential Power Type III noise component significantly outperforms all of the other models. Interestingly, we find that the city, country, road topology, and detector location have virtually no impact on model performance and fit quality, which is very convenient for model selection. The only factor of relevance from those that we studied is the effective occupancy coverage of the data. We conclude that certain models specified judiciously within FitFun can successfully capture the functional form and noise of observed flow–density–speed relationships without the need to discard data taken during non-stationary conditions. This is particularly advantageous for urban data where stationary traffic conditions are rarely observed.
KW - Empirical fundamental diagrams
KW - Flow–density relationship
KW - Loop detector data
KW - Speed–density relationship
KW - Statistical modelling
KW - Traffic
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U2 - 10.1016/j.trc.2023.104068
DO - 10.1016/j.trc.2023.104068
M3 - Article
AN - SCOPUS:85151304720
SN - 0968-090X
VL - 151
JO - Transportation Research Part C: Emerging Technologies
JF - Transportation Research Part C: Emerging Technologies
M1 - 104068
ER -