The extension will start from the end of Udon Rattaya in Bang Pa-in district, pass through Phra Nakhon Sri Ayutthaya district and end at Bang Pahan district where it will connect to Highway No.32.
The authority also plans to create a direct connection to Bangsai Arts and Crafts Centre as well as improve the current expressway over a 16km-section between Bang Poon and Bang Sai, according to Exat governor Aiyanat Tinapai.
He said the project will provide alternatives to the public and improve the logistics for goods transportation.
The Exat will sign a memorandum of understanding with Ayutthaya province on Wednesday.
Ayutthaya Governor Withaya Pewpong said the new road network would help stimulate the economy in the province and bring convenience to visiting tourists.