Copying my own content.
There is at least half a dozen threads and even more time estimates
And it stands for more than two years!
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From the central intersection Mittraphap and HW 12 it is 22 km northbound on the road.
From the northern ring exit onto Mittraphap it's a about 14 km.
Distances include the detour for the U-turn.
Location:
16.589027, 102.818511
https://goo.gl/maps/uwYGgrBfTQVM8TFW7
Quite a distance from the center.