Do you really need such procedures? The problem comes when specifying a distance. Will it be from any part of the aircraft? Will it be at any speed? Regarding enforcement, if you fine or sack people, like some idiotic airports love to do, will you un-wittingly force drivers to travel faster than is sensible?
The approach you should take must fix the real problem, and that is to avoid contact between aircraft and vehicle. Collisions occur because the relative bearings between those involved remained constant before impact. So may I suggest the following.
1. Set a realistic speed limit, one that will enable any ground vehicle to stop using its handbrake only in a reasonable distance (say 10 metres). Insist all vehicles have two braking systems.
2. Train airside drivers regarding constant bearing.
3. Show drivers the blind spots of aircraft.
4. Have well marked aircraft stands that must be clear before aircraft are moved thereon, either under their own power or by tug.
5. Wherever you do have vehicles crossing the paths of aircraft use time as the separator (like 10 bananas - sounds flippant, but it's an easy message to get across).
6. On a taxiways, restrict crossing to specified points.
7. Off-stand, but on aprons only, allow a free-for-all but insist on the time and speed limitations.
8. At times of reduced visibility, insist on lights being used by all vehicles.
9. Dump the ridiculous and half-witted flashing light policy used at virtually every airport. It has no effect. Instead reverse it and use it to highlight a hazard. Instead, use a flashing yellow or preferably red beacon to show a vehicle has broken down. Insist on battery powered LED beacons. Let pilots know about this.
10. Prohibit the sacking and fining of errant drivers. People make mistakes. Using training, education and other methods to achieve compliance.
By taking a common sense approach, you will have a workable but safe airfield, devoid of petty rules.
PM