Looking south toward Lat Phrao intersection, a northbound lane is closed Monday.

BANGKOK — Construction of a new extension linking two elevated rail lines over one of Bangkok’s busiest crossroads took off Monday morning, with impacts on road traffic there likely for the next year and a half.

Starting this morning, one lane was closed to traffic for the construction of 26-meter high pylons that will carry the tracks over the tangle of roads and expressways at Lat Phrao intersection. While only the innermost northbound lane just north of the junction is closed for now, police said others would be out of service as the project moves forward.

So far the impact seemed negligible, according to a police officer in charge of road traffic in the area.

“The company [Mass Rapid Transit Authority] closed down only several lanes,” Wissanu Thongnuam, traffic inspector for Phahonyothin police, said by telephone. “There’s no problem so far.”

Nevertheless traffic cops have been placed at all U-turns around the intersection to direct traffic flow, Lt. Col. Wissanu said.

Surachet Laophulsuk, Assistant Governor of the MRTA, said another lane will be closed in front of the Thai Military Bank headquarters south of the intersection.

The extension will connect the existing BTS Skytrain system at Mo Chit station to the new elevated Green Line extension being built just north of the intersection.

Construction of the extension, which will soar over the intersection at the height of an eighth-floor building, is expected to be done by August 2018, while the Green Line itself will be finished by February 2019.

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