This is an open access article distributed under the CC BY 4.0
Speed performances and characteristics of traffic have mostly been considered as homogeneous across vehicles. In
countries where the roads are dominated by mixed types of vehicles, the heterogeneity needs to be considered. This
study is aimed at modeling how traffic heterogeneity as captured in speed, speed deviation, and traffic volume determines
the fatality rates and accident rates. Traffic volume, road geometry (bendiness, hilliness, bend density and
hill density) and road surface condition (represented by IRI) become the independent variables in a simultaneous regression
using structural equation model (SEM). SEM is adopted to represent the hierarchical causal effects between
the independent variables and dependent variables. The data cover inter-urban roads in eight provinces in Indonesia
from 2012-2016 and 2019. Speed is not significant in predicting accident rate, and speed deviation is not significant
in predicting fatality rate. An increase in speed deviation lowers the accident rates; an increase in speed increases
fatality rates. Road geometry and traffic volume negatively impact the speed deviations of all vehicle categories, indicating
that when there is more traffic on the road, the speeds of all vehicle categories become more homogenous.
Bend density, bendiness, hill density and hilliness negatively affect both the speed and the speed deviations of the
vehicles of all categories The findings of the study can contribute to traffic policing and traffic safety improvement
schemes for heterogeneous traffic.
This research was funded by UI PUTI Doktor Grant 2020,
contract number NKB-663/UN2.RST/HKP.05.00/2020.
The Authors would also like to thank the Project Management
Unit of the Australian-funded “EINRIP MONITORING
& EVALUATION PROGRAMME, Fifth Monitoring
Survey, Final Report 2017” for the permission to use
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