Mae Rim is hell on earth for drivers, but easily avoided by taking the 1001 from Chiang Mai and cutting across to Mae Tang.

Head north till you come to the new 1414 to Mae Tang. It isn't open yet, but you continue a short distance to the klong, and take a left onto the road that runs beside it. Take the first road to the left ( opposite a bridge ), it looks like someone's drive, but it is a road, then after a hard right turn take the 3rd road to the left. That comes to a T junction and turn right. Pass Soi 15, to the next left turn and cross the new bridge. Follow that road to the 107. No right turn, so head left to the traffic lights on the junction to Mae Hong Son to U turn and continue north. You will see where the unopened 1414 comes out at the lights. It'll be so easy once that is finished.

You won't find that route on a driver's map and it's not sign posted, so check it out on the internet. The new bridge isn't marked on the internet map I used, but the locals will help out if you ask for directions to Mae Tang.

Coming back is more tricky to find the entrance, so might pay to go north the first time so you know where to go coming back.

I was going to do that very thing just that last Monday. However, instead of the road 1414 being closed before the bridge under construction (the detour referred to by OP), it was barricaded right back at the turnoff from the Prao road. Luckily we were headed to Fang, so we were able to proceed via Prao and not have to go back all those kms to the Mae Rim turnoff.

 

If it's just to avoid Mae Rim, at the moment it's a very loooong detour!!! (ie. don't try it until the road is reopened.)

Route 1414 will be very useful, once it opens, although we'll see more traffic down Route 1001 through Mae-Jo.

 

 

I was going to do that very thing just that last Monday. However, instead of the road 1414 being closed before the bridge under construction (the detour referred to by OP), it was barricaded right back at the turnoff from the Prao road. Luckily we were headed to Fang, so we were able to proceed via Prao and not have to go back all those kms to the Mae Rim turnoff.

 

If it's just to avoid Mae Rim, at the moment it's a very loooong detour!!! (ie. don't try it until the road is reopened.)

You must have misunderstood my directions. The "new bridge" I refer to is NOT on 1414. It is on the local narrow roads, but has been built recently.

Following my directions, go along the road beside the klong. At no time is it necessary to go on the 1414, unless you have a m'bike and can bypass the barriers.

The 1414 is closed hard to cars at the moment at the Ping River.   The large new bridge on HWY-1414 over the river Ping has barricades right before it so you don't be able to cross the Ping River there to get to the HWY-1095/107 intersection.   You can cross the Ping River just north of the 1414 at the rebuilt bridge across the Ping River if you have a car.     No problem taking a motorcycle all the way through on HWY-1414 as the barricades have openings big enough for motorcycles.        

There are also small bridges at
Wat Pothinmit (Turn left off 1001 at Mae Faek Mai)
Wat SuWannaWat
Wat SriSaiMoon (Turn left off the 1001 at the crossroads after Mae Faek)

Which are after MaeJo and bypass Mae Rim.

That road project south of Mae Rim has to be one of the worst organized efforts in Thailand, and they keep adding projects on either end to make the traffic problem worse.    Appears no work goes on during the weekends or at night so we can expect it to be a mess there for years.

The roadwork will be done next year and will create an underpass on 107 similar to the ones built on the Inner Ring Road.  Yes, it is a nuisance but badly needed.  Once that is done, they'll perform the same renovation along Highway 1001 (Mae Jo Road).

This Google map shows the new cutoff, although the view is a few months old.  The old bridge (at the top of the screen) had partially collapsed years ago, and is now totally rebuilt and even newer than the "new" cutoff, which, as others state, is not yet quite finished.

 

http://goo.gl/maps/d00I5

This Google map shows the new cutoff, although the view is a few months old.  The old bridge (at the top of the screen) had partially collapsed years ago, and is now totally rebuilt and even newer than the "new" cutoff, which, as others state, is not yet quite finished.

 

http://goo.gl/maps/d00I5

 

Good catch there on the new Google aerial photo update!  The new cutoff, HWY-1414 is barricaded right at the 1001 so the only way to get to the rebuilt bridge is via Klong Alley, which is the next left after the new cut-off going north on the 1001.   

I go through there most days. Single lane and most of the time it keeps moving. (10am to 3pm)  Not to bad really.  Look forward to it being finished.