Based on my past life as a facilities engineer, I’d expect they are all on a common circuit. The lights are connected with a single piece of EMT (electrical metallic tubing, AKA conduit) that runs from the eastern side of the tunnel out to some (yet undetermined) connection box with the likely switch (photocell or timer) and power source. One of the attached photos shows the conduit emerging from the eastern portal to the tunnel.
The lights were/are high pressure sodium, and they are generally pretty efficient. If the bulbs are just 100W (a reasonable assumption), the circuit would only pull 1100 watts. I could (caveat – I am not an electrician but can short out your TV) do that with a #10 wire fairly easily (accounting for the losses of the wire length).
Given the potential for damage to the light fixtures, it seems prudent to consider locating the fixtures somewhere where they were less accessible to potential vandals. There are some alternative approaches down Four Mile Run near the intersection with the MVT that could inform the discussion.
All that said, I think the rider community might want to occasionally ride over to the bridges over the trail with a broom that could brush off the spider webs and other crud from the lights. The photo shows one of the lights under Glebe that might benefit from such a cleaning.
Dana
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