I deal with this all the time. FWIW, here's the "order" of design I would recommend:
1. Hold design to 10% max.
2. If you need to go steeper than 10%, having pavement and south facing is most desireable. Anything you can do to increase sun exposure is a plus (including removing vegetation).
3. If you have to go steeper, but do not have good sun exposure, try to keep the steeper portion of the driveway away from the driveway/road intersection, to give vehicles coming down the driveway an area to stop, before sliding through the road and potentially hitting another vehicle. For example, I would rather design a road with a 30'-40' flat area (<5%) at the road intersection, and then 14% for 200' up to the house, than having a 250' driveway with a straight slope from house to road at 12.5%.
4. If you lack sun exposure, gravel is actually better than asphalt (doesn't ice up as easy).
5. Finally, if it's economically feasible, you can heat the driveway.
Also, be very careful with liability!!! If you design a driveway, and emergency vehicles are unable to access the house due to an improper design on your part (i.e. too steep, insufficient cl radii, etc.), you could be held liable. So IF you go over a 10% design, limit your liability before you sign/stamp.