The project with a total length of 49.6 kilometres in the Sukhumvit, Phahon Yothin, Phayathai, Pathumwan, Chong Nonsi and Rama III districts that started in 2008 was projected to be completed last year.
"We could not close the roads for construction, so we have only five hours for construction each day, meaning the project will definitely be late," said Mr Somchai.
He said the MEA will propose the new government provide more support in facilitating the construction through easing of restrictions.
The MEA was also assigned by the government to lay an underground transmission line along Ratchadaphisek Road from the Asoke to the Rama IX intersection, next to the subway line in a project worth 8.89 billion baht.
"This project is projected for completion by 2020, but if we operate under the same conditions, I think it will take more than 20 years to finish," said Mr Somchai.
The utility also conducted a feasibility study to expand 129.4 km of underground power transmission lines in inner Bangkok and business districts, which would cost 140 billion baht.
The MEA announced a 2014 budget of 40 billion baht, with the bulk slated for upgrading transmission lines and installing underground lines.
On Monday, the utility announced the results of the MEA Energy Saving Building Award that aims to encourage energy efficiency and electricity savings. The award attracted 47 participants in 2014 including office buildings, hospitals and hypermarkets.
Last year, 10 participants saved a combined 4.7 million units of electricity worth 18.2 million baht. Att Thongtang, the chief executive of Phyathai Hospital Group and Paolo Memorial Hospital Group, said last year Phyathai 3 hospital saved 1 million units of electricity worth 18 million baht. The hospital consumed 11.95 million units per year. The group operates five branches of Phyathai hospitals and three of Paolo hospitals.