It looks familiar but haven't been for some time so may well be wrong but guees its is somewhere on the Mae Taeng river.
Bridge over the Kok river between Chiang Rai and Thaton? But the far bank looks a bit different.
Can think of quite a few bridges like this, but this one is by far the best maintained, have a stab and say the bridge across the Kok river passed the elephant camp / karen village in Chiang Rai ?