The B6118 is a largely rural B-road to the east of Huddersfield. It not only serves as an unofficial bypass of the eastern flank of the town, but also serves to join--if you include half a mile of the A62 at the B6118's western end--the A644 (and thus M62J25) to the A637 (and thus M1J38). In effect, then, it forms the middle section of a route for those wanting to take a short cut, saving 14 miles, from the M62 to the M1 (roughly the line of what would be the Flockton Link) and thus the road carries far more traffic than its 4-digit B-road status would suggest. This heavy use (it also carries quarry traffic) and its winding and often narrow course is likely the reason it's signed as 40mph for almost its entire length. Accidents are frequent.
The road starts at traffic lights in the Huddersfield suburb of Bradley, where it meets the A6107 (former B6114) and A62. It heads south along Colne Bridge Road and crosses the Manchester to Leeds railway line, the Huddersfield Broad Canal and the River Colne in quick succession. The road then climbs up onto the moors and goes through Upper Heaton before skirting the edge of Kirkheaton. Here it crosses a minor road at The Blacksmith's Arms at the only other set of traffic lights on its route. The road now continues roughly southeastwards across the moors. After a couple of meandering miles the village of Grange Moor is met. Here the speed limit drops to 30mph and the road bends sharply to the right in the village before the road widens and the speed limit increases to 50mph for a short burst. A business park is passed to the left and the route ends at a roundabout where it meets the A637 and A642 at another Blacksmith's Arms.