A Clustering Analysis of Speed Distributions and Emission Estimation Based on Traffic Performance Index

Few efforts have been made to quantitatively analyze the relationship between traffic congestion index (TCI) and emissions in urban traffic networks.This study develops a method to derive speed distributions for TPI-specific traffic patterns based on massive floating car data (FCD).The relationship between speed and emission factors is quantified based on massive data of vehicle activity and emissions.After analyzing influencing factors of traffic performance index (TPI) and emission factors,speed distribution is identified as a bridging parameter between TPI and emission factors.In order to reduce the uncertainty of the TPbderived emission factors,a K-Means clustering method is applied to classify speed distributions of the TPI-specific traffic pattern by analyzing factors influencing speed distribution.It turns out that when sample data is clustered by road classes,weekdays/weekends,time periods (06:00-12:00,12:00-22:00 and 22:00-06:00),the coefficient of variation of speed distribution (CVSD) decrease by 10.1 %,13.6 %,and 14.6 %,respectively and the coefficient of variation of emission factor (CVEF) decrease by 10.1%,13.4%,and 14.2%,respectively.Emission factors of the TPI-specific traffic pattern for different classes of roads are calculated under different clustering criteria.