The B9170 is a downgraded A-road and as a consequence is of a pretty good standard. The section that currently runs from Inverurie to New Deer was formerly classifed as A981, and the section that runs from New Deer to Turriff was formerly classified as the A948. These two roads were truncated and now terminate at New Deer, giving rise to the L-shaped B9170.
We start on a straightened section of the A947 at Darra, a short distance south of Turriff, and head northeast alongside the Idoch Water; this is crossed about a third of the way to Cuminestown. Before reaching the village we cross the burn again (now called the Burn of Monquhitter), after which the B9027 bears off left. A couple of sharp bends take us along Main Street and High Street in Cuminestown, then the road winds back into open country.
A few miles further on we reach New Deer where we TOTSO right on the near side of town; ahead is the A948 and the A981 heads left. We soon return to the fields and continue on slightly west of southwards. This section is hillier than before. Presently we descend into the valley of the River Ythan and enter Methlick. Just before crossing the river the B9009 comes in from the right and multiplexes along our road onto Main Road. We then TOTSO right and that road continues ahead to pass the church.
We climb out of the valley and continue southwards. By Formartine's café and farm shop the B999 turns left and we then follow undulating terrain for a couple of miles to a roundabout, where we return to the A947, which has got here in under two-thirds our distance. Originally there was a multiplex through town but we now continue ahead onto the Oldmeldrum Bypass, opened in 2007. However, the bypass only goes round the west of the town so is of no use to either of the town's two A-roads.
After crossing the A920 at a roundabout, a further roundabout is reached where we rejoin the original route of the B9170. We continue southwest to run under the Hill of Barra and reach a roundabout, from where an unclassified road, opened in 2015, heads west to reach the B9001. It's not much of a bypass for Inverurie, however. We pass Inverurie's northern suburbs then cross the River Urie before running through an industrial estate and over a bridge over the Aberdeen to Inverness railway line; the station is adjacent.
We quickly enter the Market Place where the B9170 runs ahead to reach the B9001 (former A96) High Street. However, this section became a spur when the A96 bypass was built and the B9170 extended west to meet the new road. There's therefore a badly signed TOTSO right past the Town Hall, after which we meet the B9001 at a roundabout. There's a brief multiplex along West High Street to a mini-roundabout; our road is apparently dominant but it's not particularly clear. We then continue along Blackhall Road to end at a roundabout on the A96.