A grading system for way-marked off-road cycling trails has been adopted in the UK, and is used by official bodies such as the Forestry Commission and IMBA-UK. It was originally developed by Cyclists' Touring Club (CTC) employee Colin Palmer in June 1999, based on a system widely used for grading cross-country skiing routes.
| Colour | Grade | Suitable for | Trail type | Gradient | Surface/width | Acceptable hazards | Distance | Maximum climb | | Green | Easy | Non-cyclists and families, children aged 4 or above riding solo, bikes with child seats or trailers, touring bikes, bikes for those with disabilities. | Rail trails, towpaths, reservoir trails, estate or forestry tracks, traffic-quiet roads, and those regulated by bylaws or other restrictions. | Shallow climbs and descents capable of being ridden by children and non fit adults. | Blacktop or compacted limestone or gravel. Essentially smooth with a minimum content of loose surfaces. Normal width 2 - 3 metres. | These trails should carry a very low risk. Any unavoidable hazards should be identified in promotional literature and through notices at trail head and site of hazard. | 5 – 10 km (3 – 6 miles) | 50 metres |
| Blue | Moderate | Occasional cyclists with some experience of road use or easy trails, reasonably fit families, children aged 10 or above riding solo, suitable for mountain bikes, hybrids or robust touring bikes. | As 'Easy' plus bridleways and byways and un-surfaced unclassified roads. Lightly trafficked lanes. | Shallow/moderate climbs with short sections of steeper climbs which may have to be walked. | Mostly stoned surfaces, 10% earth based singletrack, 2 metre width. | Some loose surfaces, ruts, potholes and or tree roots maybe expected. | 10 – 20 km (6 – 12 miles) | 100 metres |
| Red | Difficult | Regular cyclists with experience of moderate trails suitable for off-road quality mountain bikes. | Any usable trail with pushing or portage unlikely to exceed 2% of total distance. | A wide range of climbs and descents of a challenging nature. | Widths from 1 metre and any usable surface. Likely to include singletrack and other technical sections. | The route should be judged on the basis that a reasonably experienced rider riding within his/her level of skill and prevailing ground conditions, would not be expected to fall. | 10 – 50 km (6 – 31 miles) | 500 metres |
| Black | Severe | Expert mountain bikers who will expect and relish technical challenges. | Any. But with the expectation of technical riding which could include unforgiving terrain, severe climbs and descents, or considerable distances. | Any rideable or usable gradient. May include 'drop offs'. | Mostly off-road. Expected to include a significant proportion of singletrack, with challenging surfaces. | Hazards are expected as assessed and agreed by an expert user. Falling off will be expected. | 1 – 100 km (2 – 61 miles) | 1000 metres |
A solitary major hazard (e.g. one steep hill or a difficult junction) will not necessarily raise an otherwise 'Easy' route into a 'Difficult' one.