A note on tower spacing

We are asked about tower spacing more than any other technical question, usually by people who have counted the poles on a ski lift and are alarmed.

Spacing is set by span and by terrain, not by preference. On the Eastside the towers fall between 200 and 300 meters apart, which works out to roughly six per mile. Each occupies about sixty square feet where it meets the ground, on a cast foundation set back from the trail edge.

The number people expect is higher because the reference point is wrong. A chairlift on a mountain has towers every eighty meters or so because it follows a slope. A line over a former rail corridor is running across ground that was graded flat a hundred and forty years ago, which is the single most useful thing about the Beltline for this purpose. Long spans are cheap when the ground beneath them does not move.

Cabins clear the trail surface by a minimum of eight meters at the lowest point of any span. In the cut sections the towers are shorter and the clearance comes from the topography rather than the structure.

None of this is settled. Spacing will change as the survey work is refined, and the revised figures will go into the next memorandum rather than onto this page.