Why is my trans leaking?

I let it sit for a few minutes, fired it up and then ran through the gears. Went undernieth the car again and the puddle got slightly bigger. Any idea what could be the problem, and is it safe to drive it 3 miles up the road to my mechanic?
I'm a lil nervous.
Start the car up cold and go straight to the shop unless the leaks real bad then you should call a tow truck which might be the better option anyway ,






