臺灣高速公路坡度路段設計之代表性車輛

REPRESENTATIVE VEHICLES FOR DESIGN OF GRADE SEGMENTS ON TAIWAN’S FREEWAYS

為協助公路坡度路段設計及服務水準分析，交通部運輸研究所（以下簡稱運研所）乃進行一計畫以研究發展一微觀模擬模式，此模式稱為Traffic-on-Grade（TGS）模式。TGS模式採用Speed-on-Grade（SOG）模式估計車輛在坡度路段之瞬間旅行速率。公路坡度路段之各種車輛自由速率的變異，為一公路設計之重要考量，因為其與交通安全及服務水準密切相關。許多國家都利用一些特定質量與馬力比值的代表性車輛進行公路設計。臺灣於公路設計方面，對於使用哪些代表性車輛一直不太清楚。本研究利用SOG模式及國道1號之平均自由速率特性，探討適用於臺灣高速公路坡度路段設計之代表性車輛。模擬結果指出，聯結車、大貨車、大客車及小車（機車除外）的代表性車輛質量與馬力比分別為125、64、75及50kg／kW。本研究並提出代表性車輛在坡度不變之上坡路段的自由速率與旅行距離關係，以協助坡度路段之幾何設計。

To assist in the design and level-of-service analysis of highway grade segments, the Institute of Transportation (IOT), Ministry of Transportation and Communications initiated a project to develop a microscopic simulation model. This model, referred to as Traffic-on-Grade Simulation (TGS) Model, employs Speed-on-Grade (SOG) sub-model to estimate the instantaneous accelerations and speeds of a vehicle on a grade segment. Variation of the free-flow speeds of vehicles is an important consideration in the design of grade segment because it affects not only traffic safety but also level of service. Many countries have specified representative vehicles with various weight-to-horsepower ratios for highway design. For the design of Taiwan’s highways, it is not clear what representative vehicles should be used. This study uses the SOG model to identify representative vehicles that exhibit the average free-flow speed characteristics observed on Taiwan’s National Highway 1. Simulation results reveal representative trailer-truck, single-unit large truck, large bus, and small vehicle (excluding motorcycle) have weight-to-horsepower ratio (in kg/kW) of 125, 64, 75, and 50, respectively. Characteristic relationships between free-flow speed and travel distance of these vehicles on uniform upgrades are presented for design applications.