Light Rail Lines

I just spent a pleasant couple of hours looking at light rail lines. There are a surprising number coming in at greater distances than I expected. I thought the 'minimal operable segment' would be about 15 miles. I did not see that very often. Lines actually coming in between 7-20 miles, with the 18-20 range well attested to. (Not counting the bizarre Tacoma Link at 1.6 miles). Difference in initial distance seems to be the availability of an existing rail corridor. If you've got one, it's easy to go longer. Without one, using ROW from a freeway, or street right of way, the costs and complexities are higher, and the initial line tends to be shorter.