There actually isn't in regards to safety. This has been discussed greatly in the Laws/HTA section (I'll go looking for the link when I get a chance) The mandate for distance between signals is set out in CMVSS for new vehicles and manufacturer's must follow this, but it doesn't actually apply to safeties. The issue will be trying to convince a technician who firmly believes it does to write the safety. maybe suggest he call the ministry for clarification.