In the aftermath of a windstorm that interrupted service on over 40% of Puget Sound Energy’s transmission system, the regulator ordered an investigation, which was to evaluate options for hardening the electric system.

This study quantified the extent of tree exposure along the transmission system and examined the correlation between various field measurable variables and tree-caused outage frequency. Based on the significant correlations, it is concluded that only mitigation, which reduces the extent of tree exposure holds the potential to significantly decrease tree-caused service interruptions during major storms...