The information was entered into a spreadsheet, reading the Risk Factor for 25 feet and 35 feet from the Line Strike Probability chart. The spreadsheet shows that increasing the clear width 10 feet would improve line security 52%.

Based on the assumptions that the trees can be removed by feller buncher for $8 per tree and that chainsaw removals cost $60 per tree, a cost per mile was derived.

An investment of $2424 per mile (one side only) is a substantial investment. If reliability is critical on this line it might be justified by the reduction in tree-related outages. Where widening is going to really have a positive impact is during storms. Even severe weather related tree-caused outages will be reduced 52%.

ECONOMICS OF WIDENING
 
What if avoided storm restoration costs are considered? Can an economic argument be made for increasing the clear width?

Depending on the average annual restoration costs, it is possible that over a period of time the widening has a positive rate of return. The graph below shows the 10 year net present value for six different annual restoration costs for clear widths from 25 to 75 feet.

Based on this graph, if the average annual storm restoration costs for the section of line under consideration, are between $600 to $800 per mile, the best return on investment is obtained at a clear width of 40 feet. For sections of line where the average annual restoration costs are $300 per mile or less, increasing the clear width improves reliability but over ten years the savings in restoration costs are less than the widening cost.