"The worst offenders are motorbikes, which have a huge impact on footpaths and even on the tracks that they are allowed to share with walkers"
Hang on a sec - they are roads that walkers use surely?
BOAT's in UK, Green Lanes in IoM?
From IoM Govt website.....
"There are many miles of ancient "unmade roads" in the Isle of Man. They are rights of way through the countryside, not just for pedestrians but also for other classes of traffic, such as 4 x 4's, motor cycles, mountain bikes and horses. These unmade roads are known as "greenlanes" but some of them are classified as "Greenway Roads" on which vehicles are restricted."
Cheers