Trees And The Electric Grid

The Article X briefing before the City Plan Commission was not presented as planned on May 18 and has been held-over to June 8.  But the day was not all lost when a speaker did manage to survive the marathon hearing session to get to the final public comment period.  The statements made were regarding the local electric utility grid manager, ONCOR, and the Public Utility Commission mandates that direct, or influence, their activities.  Concerns over how the utility can conduct its mission with the provisions of Article X are well founded considering most ordinances in the past have drastically ignored the conflict of trees and electricity.  I hope we have managed to answer some of these issues.

In the Street Buffer Zone, the average buffer depth requirement allows for a varied buffer to place trees between parking spaces.  This allows for the large or medium tree to be spaced a MINIMUM of 20 feet, or 15 feet on center, respectively, from the alignment of the nearest overhead electric line.  It provides growing space for the tree and a little more breathing space for the electric system.  Maintenance of the tree would mean a smaller percentage of tree canopy for removal to keep the utility line in the clear.  The property owner and the community retain the benefits of the tree.  Legacy trees must be maintained a minimum of 30 feet from the overhead electric utility.

The proposed upgrade to Sec 51A-10.104, Soil and Planting Area Requirements, specifies tree location distances from underground and overhead utility lines.  Overhead transmission and distribution lines are simply indicated as 'overhead electric lines' where legacy* trees must be planted a minimum of 30 feet from the closest point of an overhead electric line; large trees at 20 feet; and medium trees at 15 feet, distance to center of the tree.  These standards would be applied to all new construction.

These minimum standards are intended to reduce the maintenance demands and risk, as well as tree canopy loss, which typically result from large trees planted under the lines.  The new ordinance is silent regarding small tree locations to overhead electric lines.  

The complications we find on development projects with moving the tree locations further from the lot boundary may fall under questions of available space for the use of the property.  For balance, the street buffer zone now becomes an area of shared space for both landscape purposes and site uses. The proposed ordinance tries to take the current landscape provisions and make these locations more pliable to parking and visibility demands while also assuring appropriate aerial and ground space for the trees.  

The street buffer zone will measure automatically from the street right-of-way (typically the property boundary) instead of the street curb (as is applicable today), but allows the use of the parkway to meet requirements unless other restrictions do not prevent its use.  Essentially, the parkway (being the zone of most utility conflicts) conditionally becomes an option when planting on the property is not practicable.

Generally, moving the trees further from the right-of-way would be more suitable for the utility, but would also reduce the impact of the tree as a landscape feature and filter between the active street and the land use.

Other regulations apply to the electric utility including Sec 51A-10.140, Defenses to Prosecution, which allows for the removal of trees without permit for maintenance of a public utility, or for a tree which interferes with service provided by a public utility in a public right-of-way.  

Elsewhere, the regulations for utility and public service uses in Sec 51A-4.212 place only limited requirements for landscaping, but generally landscape regulations are not applicable to properties like substations and others listed under the utility service uses. Where a Specific Use Permit (SUP) is required for such a facility, this may vary.

On lots less than two acres with single family or duplex uses, trees are not regulated.

Of course, Article X is not the only landscape regulation in the City of Dallas and helpful solutions we may find for most sites may not be applicable in others (cough - Oak Lawn - cough).

*Legacy tree means a large or medium tree planted in a landscape area for the specific purpose of actively establishing and maintaining unencumbered sustainable large shade trees for future generations.  It is referenced in Sec 51A-10.101, 10.104, and 10.135.

Pathway to power (ONCOR)
Understand the differences of Transmission lines and Distribution lines. (OSHA)
How the electric transmission system works (Minnesota Electric Transmission Planning)