台灣高速公路系統鋪面面層全線包含匝道大部分使用Open-Graded Asphalt Course (OGAC)，其排水能力較Dense-Graded Asphalt Concrete (DGAC)佳，於雨季時能減少因降雨於面層形成水膜及積水造成之高速行駛時水漂及水滑現象提升行車安全，然而匝環道屬車輛加速及減速之路段容易造成OGAC產生剝脫及坑洞等其他破壞。本研究主要是探討DGAC應用於匝環道之面層而不加鋪OGAC的可行性，DGAC不同於OGAC其為非透水鋪面，故首先須考量匝道之線形設計，了解透過線形變化能否使DGAC順利排除於鋪面上之降雨，接續針對鋪面若無法排除之雨水形成之水膜是否將影響駕駛行車之安全性，都是值得探討的議題，本研究將透過車輛煞車距離與設計安全煞車距離兩者進行檢視，了解DGAC使用於面層之安全性，最後透過主線及匝道抗滑檢測與鋪面養護刨鋪之時間進行分析了解DGAC之耐用性是否較OGAC佳。本研究於台灣高速公路北區養護工程分局轄區內之匝環道進行現地試鋪，藉由鎖輪式抗滑儀測定抗滑值，分析其與交通量、使用年限與路面線型之關聯，初步研究成果顯示兩者鋪面類型皆能符合匝環道於雨天所設計之最低摩擦係數。由本研究結果顯示，匝環道面層使用DGAC之摩擦係數不低於現行要求所使用之OGAC，且OGAC之摩擦係數下降趨勢較DGAC為明顯，透過成本分析發現面層材料使用OGAC之總成本將較DGAC高出5倍，綜合上述各點，高速公路匝環道只鋪設密級配瀝青混凝土作為上面層是有可行的。;The Open-Graded Asphalt Concrete (OGAC) is used in Taiwan freeway pavement; it can reduce the puddles of the pavement to avoid the hydroplaning in rainy season. Compare with the Dense Graded Asphalt Concrete (DGAC) it can improve the safety of driving; nevertheless, the ramp is the section of the vehicle acceleration and deceleration, the OGAC will easily occur potholes, raveling and other distress. This study explores whether the DGAC pavement on ramp is qualified in safety and can improve the durability. In addition, with the geometric design of the ramp, whether the pavement surface can maintenance the friction for the safety in case of rain. The friction of pavement will decrease by the water film; furthermore, the OGAC has the slower trend of friction decrease than DGAC. This study used the lock wheel skid tester to measure the skid number of pavement surface at the ramp of Taiwan Freeway Bureau Northern Region Branch Office, analyzing the relation of traffic, time and the road type with the data of skid number. To know whether both kind of pavement surface is measure up to the minimum friction of the ramp design. The study result shows that the friction decrease trend of DGAC is slower than OGAC; moreover, most of the friction of DGAC at the ramp is higher than OGAC. It is found that the total cost of OGAC will be 5 times higher than that of DGAC. Based on the above points, dense-graded asphalt concrete was feasible on the freeway ramp.
