In their announcement, the Royal Thai Navy explained that all northbound lanes on Route 402 – including Thepkrasattri Bridge – will be closed from the Tha Chatchai Check Point to the Khok Kloi Intersection in Takua Thung, Phang Nga, from 4am to midday on Saturday.
During that time, the southbound bridge, Srisoonthorn Bridge, will be open for traffic one lane each way.
From midday to 5pm, one northbound lane on Route 402 – and across Thepkrasattri Bridge – will be opened, the Navy said.
After 5pm, all roads are to re-open to traffic as usual.
In Phang Nga, from 5am-midday, Route 3006 will be closed to traffic entirely from the Khao Pilai intersection to where the road become Route 2013, which will have one lane will be closed to the office of Provincial Waterworks Authority in Tambon Na Toei, Thai Mueang District.
In its announcement, the Royal Thai Navy Third Area Command apologised for any inconvenience caused while the triathlon is being held.
In total, 1,538 individual athletes and 230 teams have registered to take part in the triathlon, which sold out early last month.
Many of the competitors are Navy servicemen, but entry was open to all, including foreigners.
The Navy Warrior and Team Navy Warrior race categories will start at 6:30am, giving athletes 17 hours to complete 3.8km swim, 180km bike ride and 42km run.
The Olympic Distance and Team Olympic Distance entrants will start at 7am, with 5 hours and 30 minutes to complete the 1.5km swim, 40km bike ride and 10km run.
Entrants in the Duathlon will get underway at 7:15am, with 5 hours and 30 minutes allowed to complete the 5km swim, 40km bike ride and 10km run.
The Sprint Distance racers will start at 7:30am, with entrants allowed 2 hours 30 minutes to complete the 750m swim, 20km bike ride and 5km run.
Ages in the Men's categories start at 15-24 years old and continue in five-year age brackets up to 59 years old. A separate category remains for male athletes aged 60 or older.
The Women’s events also start at a 15-24-year-old age category and continue in five-year age brackets up to 49 years old. A separate category remains for women athletes aged 50 or older.