The 5.5-billion baht Srinakarin-Rom Klao Road -- a 12-kilometre long road which links Hua Mak Road to Rom Klao Road in eastern Bangkok -- opened to the public on Thursday, four years after construction began.
Another 2.8 billion baht was spent on land expropriation compensation.
Bangkok governor Aswin Kwanmuang presided over a ceremony to mark the opening of the road.
This new road will help ease traffic congestion in Bang Kapi, Saphan Sung, Lat Krabang and other surrounding areas, said Pol Gen Aswin.
Ramkhamhaeng Road and Srinakarin Road often face traffic congestion due to the construction of the Orange Line and Yellow Line rail projects respectively. The new road should provide an alternative for many commuters, he added.
The six-lane reinforced concrete road has the capacity to handle 200,000 cars per day.
The final section of the road was built as a 950-metre elevated section running over Kanchanaphisek Road, also known as the eastern outer ring road, in the Saphan Sung district of Bangkok.
Thaiwut Khankaeo, acting director of the Department of Public Works of the Bangkok Metropolitan Administration, said construction began in 2015 and the first section opened to the public last year.