Kanchanaphisek Road

Kanchanaphisek Road (ถนนกาญจนาภิเษก), also known as the Bangkok Outer Ring Road (ถนนวงแหวนรอบนอกกรุงเทพมหานคร) is a highway in Thailand, connecting Bangkok, Samut Prakan province, Nonthaburi province, Pathum Thani province and Phra Nakhon Si Ayutthaya province. It consists of multiple sections, including a controlled-access toll road, and almost forms a complete loop around the Bangkok Metropolitan Area.

History
Due to the rapid economic development of Bangkok which resulted in a significant increase in road traffic, the Bangkok Outer Ring Road was conceived in 1978 as a bypass route to connect the major highways leading out of the capital city. Its construction was separated into sections due to the high costs involved in the project, with the West section being the first to be constructed, followed by the East section and the South section. The Department of Highways initially designated the highway as Highway 39, but it was changed to Highway 9 after the Master Plan of Intercity Motorways (แผนพัฒนาระบบทางหลวงพิเศษระหว่างเมือง) was drawn up in 1996. In the same year, the road's name was bestowed upon by King Bhumibol Adulyadej following the Golden Jubilee celebrations, 'Kanchanaphisek Road ', meaning 'Golden Jubilee Road'.

The Department of Highways maintains West and East Kanchanaphisek Road, while the Expressway Authority of Thailand maintains the South Kanchanaphisek Road.

West Kanchanaphisek Road
This was the first section to be constructed in 1978, between Taling Chan district, Bangkok and Bang Bua Thong district, Nonthaburi, as part of Highway 340 to Suphan Buri. This section was later extended to Bang Pa-in district, Phra Nakhon Si Ayutthaya in 1995. The section between Taling Chan district with Bang Khun Thian district was completed in 1998.

East Kanchanaphisek Road
The eastern section was completed in 1998 as a four-lane intercity motorway with toll collection. This was expanded to 6-8 road lanes in 2010 to handle the increased traffic after the opening of Suvarnabhumi Airport. On 15 February 2022, it was the first highway which the Department of Highways introduced the multi-lane free flow system (M-flow) to reduce congestion at the toll gates. As of April 2023, approximately 110,000 cars use the system daily.

South Kanchanaphisek Road (Kanchanaphisek Expressway)
The southern section was the final section to be constructed and is a controlled-access toll highway. It opened for trial use on 15 November 2007 and toll collection between Bang Phli - Suk Sawat began on 23 March 2009. Toll collection was extended to the Suk Sawat - Bang Khun Thian section on 20 May 2019. Kanchanaphisek Bridge, the southernmost river crossing of the Chao Phraya River is part of the highway.

According to an official EXAT annual report, the expressway was used by 79,603,350 cars in the 2022 fiscal year, with an average of 225,505 cars per day.

Kanchanaphisek Expressway
The Kanchanaphisek Expressway (South Kanchanaphisek Road) is located almost entirely in Samut Prakan province.