We have a 200 yd long driveway I'm going to put up a snow fence to hopefully stop drifts from our North side

What is the best distance from the drive.

& how far apart the T posts?

old wooden snow fence ?
prevailing winds during a storm >?
how much open field do you have it coming through

I'd say at least 100 feet.

160 feet minimum for the fence to work properly. Might need additional fence if the drift goes over the top. 8 feet max on posts, use furring strips against the fence to hold on posts.

Heck we have fence up within 25 yds of the drive we need to snow fence. Not near 160 ft from the driveway.

and you have snow drifts in the driveway.

Depends in height I'd the fence, dominant wind and terrain. We'd call the county works department and they would give us good info. Good enough that we really barely had to plow the drive.

You get 10 ft of horizontal protection for every 1.0 vertical feet of windbreaker.
I set my 4' snow fence about 35-40 ft back from my road.

A drift will extent up to 35x the height of the fence, 4' fence can extend the drift 140'. Closer that that distance, will have drifting in the road.

I worked for the Soil Conservation Service from 1979 until 2009, during which I planned, designed and installed Conservation practices for water and wind erosion.
FWIW, go to your state NRCS website and check out the FOTG (Field Office Technical Guide). For example, MN NRCS, etc. Home page......FOTG.....

Everyone forgets the[b] wing plane effect [/b]on blowing snow
Having it so wind can go over and under created a swirl effect and this drops the load capacity of the wind holding the snow

Just raise up the driveway a few feet.

Boco he is not on the bald ash prairie where that works

Mine are orange plastic rolls

I started with the same plastic rolls, but they became quite brittle and cracked, tore, etc. I have since changed over to the 4 ft lath snow fence. I typically set the T posts about 8 ft apart. My driveway is just shy of a 40 length from my buildings to the town road. I planted a two row windbreaker (one row of white cedar, one row of ninebark) years ago - and it helps quite a bit. If we get a lot of snow, this windbreak will fill up and eventually deter less snow drifting. My old IH 766 with a loader is what I use to own open my road. Occasionally I'll have to call the township grader in to break the really bad drifts.

The plastic just does not cut it with windy conditions as it tears when -20c
have at least one foot clearance under the fence
a slow dump of snow the fences just dont work
30 mph wind snow dump then the fence has to be 200 yds from the drive

That's about the distance I remember our road crews setting them back.

If you can plant permanent poles in the ground to wire the snow fence,you can raise it as winter goes on.
Probably no good in farm country-posts might impede cultivation?

53.5 yds from drive