City Hall plans to build a four-lane tunnel along Si Ayutthaya Road to ease the heavy traffic congestion through the main intersection.
Motorists will be able to bypass the intersection with Rama VI — which is frequently badly congested with vehicles from the eastern outskirts — via the tunnel, according to the Bangkok Metropolitan Administration's (BMA) Public Works Department.
The tunnel, which will run underneath Rama VI Road, aims to ease traffic flow through the Si Ayutthaya intersection by providing an alternative route, said a source at the BMA.
The heavy traffic flow from the western outskirts of Bangkok into the city centre and eastern Bangkok clogs the intersection and rarely lets up during the day, the source said.
Underground water pipes and electrical wires will have to be relocated, which will take one year and cost 87 million baht.
This is on top of the tunnel's 707-million-baht construction cost, and takes the total cost to 794 million baht, said the BMA source.
The Metropolitan Waterworks Authority and Metropolitan Electricity Authority will pay for the infrastructure relocation, he said.
The BMA will call for construction bids this August, and expects to start building the tunnel by the end of 2015 and complete it in three years.
During construction, two out of four lanes on each side of Si Ayutthaya Road will be closed.
Further talks on managing the traffic during construction will be held with the traffic police division, he said.
Commuters will be notified about which routes to take, and traffic flows, before work starts.