Highway 4 or Phet Kasem Road is one of the four primary highways in Thailand, along with Phahonyothin Road (Highway 1), Mittraphap Road (Highway 2), and Sukhumvit Road (Highway 3). At 1,274 km, Highway 4 is the longest highway in Thailand.
History
The construction of the road was finished in 1950 and was named "Phet Kasem" on December 10, 1950 in honor of President Ittikorn Phetkasemwithisawasdi (Tham Phetkasem), formerly the seventh director deputy general of the State Highways Department. Before that, it had been called "Bangkok–Khlong Phruan Road". President Ittikorn Phetkasemwithisawasdi was the scholar of the State Railway Department (now State Railway of Thailand). He studied civil engineering in England and returned to work for the State Railway Department and then transferred to the State Highways Department. Phet Kasem Road was built during the period when Ittikorn Kasemwithisawasdi was the deputy director general of the State Highways Department. The road was named under the policy of the government of Major Vice Hashima who named the road after the chief engineer who supervised the construction and gave the instructions.