Investigation On Vehicle Type Classification And Operating Speed Characteristics Of Mountain Freeways Based On ETC Data

Mountainous expressways undertake the primary transportation tasks between urban areas in hilly and mountainous regions,with heavy traffic volume and numerous running vehicles.Due to the complex driving environment and the variability of road alignment conditions,the accident rate of mountainous expressway is relatively high.In recent years,the trend of increasing vehicle size and weight has been observed in response to the demands for safety and comfort as well as efficiency in transportation.However,this change in vehicle characteristics and type distribution is not in line with the current design specifications of the expressway,which still use standard vehicle types such as small passenger cars and medium-sized trucks.As a result,it is difficult to represent the physical and operational characteristics of the majority of vehicles on the mountainous expressway accurately.This mismatch between vehicle characteristics and road design standards is one of the main reasons for traffic accidents on the expressway.Therefore,in this paper,we study the traffic composition,driving speed,and vehicle classification under the characteristics of increasing vehicle size and weight on mountainous expressways,which could provide a scientific basis for vehicle management,speed management,and the redesign of road alignment on mountainous expressways.Nowadays,the ETC system is widely used and can collect a large amount of traffic information,including vehicle driving speed and traffic flow,which can be further explored to analyze the traffic structure,distribution of vehicle types,and driving speed on different sections of the mountainous expressway.Based on these background information,this paper analyzes the ETC data of the Baomao Expressway section from Shuijiang to Nanpeng in July-August 2020,and further explores the traffic composition,vehicle type distribution,vehicle speed on different road sections(flat section,continuous uphill section,and continuous downhill section),and road traffic flow.Our research analyzes the distribution of vehicle types,the dominant vehicle type,the driving speed of different road sections,the speed-flow relationship,and the vehicle classification based on speed.The following results were obtained:1)In mountainous areas,the ratio of passenger cars to trucks on highways is generally stable at 3:1,with Type 1 passenger cars(small cars)being the dominant vehicle type and also the main type of passenger car.The main types of trucks are 3-axle heavy-duty payload trucks(accounting for approximately 45% to 50%),followed by 6-axle heavy-duty payload trucks(approximately 18%).Passenger cars are the main vehicle type affecting the traffic volume on mountainous highways.Traffic volumes increase on a weekly basis,with higher volumes on weekends(Friday to Sunday)compared to weekdays(Monday to Thursday).2)The speed of vehicles on mountainous highways is nonlinearly related to traffic flow,with passenger cars being more sensitive to changes in traffic flow than trucks.Based on the relationship between average traffic flow speeds,V85 speeds and traffic flow during the statistical period,a "speed-flow" relationship model was established to classify different traffic operating states(free flow,stable flow,congested flow)on mountainous highways,and determine the corresponding speed and flow rate intervals associated with different traffic operating states.3)Different vehicle types have significant differences on different longitudinal road sections.Three types of trucks are most affected on continuous uphill sections,with speed distributions showing a hump-shaped distribution related to their load status(empty/load).Type 4 passenger cars are commercial vehicles with regulated operating speeds,with a speed distribution at 92km/h showing a truncated downward trend.Speed variability is greatest on gentle slopes,followed by continuous downhill sections,and then continuous uphill sections.Greater speed variability increases the likelihood of rear-end accidents,necessitating speed management in segments on mountainous highways.On the same longitudinal cross-section,the speed of passenger cars is higher than that of trucks,making it necessary to manage different vehicles with separate lanes on mountainous highways.4)K-medoids clustering analysis was used to analyze the speed of different vehicle types on different road sections,and the results were classified into four major categories.The classification for gentle slopes and continuous downhill sections is similar,while the classification for continuous uphill sections differs from other road sections.The classifications for gentle slopes and continuous downhill sections are as follows: Class 1-Type 1 passenger cars;Class 2-Type 2～4 passenger cars;Class 3-Type 1 trucks;Class 4-Type 2～6 trucks.The classification for continuous uphill sections is as follows: Class 1-Type 1～4 passenger cars;Class 2-Type 1,3(empty)trucks;Class 3-Type 2,3(full),4 trucks;Class 4-Type 5～6 trucks.