This is really an old roadbed — not paved, but almost as good as, as long as the weather has been reasonably dry. During spring snowmelt or particularly rainy periods the trail can get very muddy.
Motorized traffic (such as all-terrain vehicles) is allowed on the trail from Sunday through Wednesday. You certainly can still run during that time, but be ready to share the trail with ATVs. There are short, non-motorized side detours you can take to minimize your exposure to that motorized traffic, but the detour trails are sometimes loose or washed out, so they can be a particular challenge for runners.