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With the growing economic development and urbanization in China for the past10years,many highways especiallyundergroundhighway tunnels are being constructed throughout the country.The underground road system in China has transcendedtheUSA,Europe and other developed countries andthenumber of highway tunnels in China exceeded1200in2013.Recently,many underground tunnel interchanges are also being constructed.Driving inthe underground highway tunnelis different than the drivingon the open highway.Although,less crashes happen in the underground highway tunnel but the severityof thecrashes is higher than the open highways.Moreover,Interchanges are critical segments ofthehighway where merging and diverging of traffic take place.Underground tunnel interchanges are different than the open highway interchanges which offeralimitedsection of tunnel highway for lane changeand diverging of vehicles.
Therefore,this study focuses on the operational performance and safety assessment ofthe underground highway tunnel along with the underground tunneldiverging area.For this purpose,themicroscopic simulation model,VISSIM,was used to analyzethe operational performance.The operational performance of the underground highway tunnel was analyzed during low,medium and high traffic conditions with different lengths of the lane changingsection100m,200m and300m before the entrance of the exit rampof underground tunnel interchange.For safety assessment,Surrogate Safety Assessment Model was used to perform the traffic conflict analysis andresults of each scenario were compared.
Fortheoperational performance of the underground highway tunnel,vehicles’delay,speed and lane changing speed measurement were made.The results show thatduring low and medium traffic conditions,travel timedelayof the trafficdo not vary significantly.But during high traffic conditions,mean travel time delaywas reduced by94%when the length of the lane changing section was increased from100m to300m.Similar resultswere obtained by analyzing the lane changing speed of the vehicles.Results show thatduring high traffic conditions,mean lane changing speed was increased from23.2km/h to51.5km/h when the length of the lane changing section was increased from100m to300m.Analysis of Variance was performed tofind the statistically difference in mean of operational performance indicatorsdue to traffic volume factor.
For safety assessment,traffic conflict techniques were usedusing SSAM.SSAM filtered the conflicts using the TTC threshold values based on the vehicles’trajectories.Results of SSAM gave very few conflicts during low and medium traffic conditions.But during high traffic condition when the length of the lane changing section was100m,SSAM reported202total number of conflicts and these conflicts were reduced by74%when the length of the sectionwas increased to300m.ANOVA test was also performed to find the difference in meanof safety performance indicators due to traffic volume.
Therefore,this study focuses on the operational performance and safety assessment ofthe underground highway tunnel along with the underground tunneldiverging area.For this purpose,themicroscopic simulation model,VISSIM,was used to analyzethe operational performance.The operational performance of the underground highway tunnel was analyzed during low,medium and high traffic conditions with different lengths of the lane changingsection100m,200m and300m before the entrance of the exit rampof underground tunnel interchange.For safety assessment,Surrogate Safety Assessment Model was used to perform the traffic conflict analysis andresults of each scenario were compared.
Fortheoperational performance of the underground highway tunnel,vehicles’delay,speed and lane changing speed measurement were made.The results show thatduring low and medium traffic conditions,travel timedelayof the trafficdo not vary significantly.But during high traffic conditions,mean travel time delaywas reduced by94%when the length of the lane changing section was increased from100m to300m.Similar resultswere obtained by analyzing the lane changing speed of the vehicles.Results show thatduring high traffic conditions,mean lane changing speed was increased from23.2km/h to51.5km/h when the length of the lane changing section was increased from100m to300m.Analysis of Variance was performed tofind the statistically difference in mean of operational performance indicatorsdue to traffic volume factor.
For safety assessment,traffic conflict techniques were usedusing SSAM.SSAM filtered the conflicts using the TTC threshold values based on the vehicles’trajectories.Results of SSAM gave very few conflicts during low and medium traffic conditions.But during high traffic condition when the length of the lane changing section was100m,SSAM reported202total number of conflicts and these conflicts were reduced by74%when the length of the sectionwas increased to300m.ANOVA test was also performed to find the difference in meanof safety performance indicators due to traffic volume.