Phetkasem Road (Thai: ถนนเพชรเกษม, also Petchkasem Road) or Thailand Route 4 (Thai: ทางหลวงแผ่นดินหมายเลข 4, AH2) is one of the four major highways in Thailand, along with Phahonyothin Road (Route 1), Mittraphap Road (Route 2), and Sukhumvit Road (Route 3). At 1,274 km, it is the longest highway in Thailand. It begins at Naowa Chamnian bridge in Bangkok Yai, Bangkok. It is named after Luang Phetkasemwithisawasdi, the seventh director general of the Department of Highways.
The provinces along the road are Samut Sakhon, Nakhon Pathom, Ratchaburi, Phetchaburi, Prachuap Khiri Khan, Chumphon, Ranong, Phang Nga, Krabi, Trang, Phattalung and Songkhla, linked to North-South Expressway (NSE) of Malaysia at Sadao pass and Bukit Kayu Hitam pass.
Phetkasem highway in Southern part (in red)
Three sections of the highway are also the Asian Highway AH2.
Thai highway network