A road maintenance envelope should be maintained to ensure that larger vehicles can safely travel along a route without striking vegetation. The envelope extends over the roadway and shoulder and is expressed as the vertical clearance. While the dimensions may vary across jurisdictions, some common maintenance envelopes (heights) are:  

  • Over Dimension (OD) route: 6.5m 
  • Urban/rural freeways and arterial roads: 6.0m 
  • Local roads: 5.0m 

The above envelopes ensure that vehicles won’t strike vegetation, but it’s also important to ensure that vegetation isn’t obscuring important signs or delineation devices. Some jurisdictions use a tiered clearance envelope system, with Primary (as outlined above), Secondary (area surrounding roadside furniture), and a Verge Clearance prevision.