by Pete
Every Red Line platform of late has an "arrow" (really just two 3"-wide pieces of tape mounted at a right angle) pointed a a survey spike with a reference number written alongside. What are these for?
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octr202 wrote:I've noticed them on the Orange and I think even some Green Line platforms in the last few weeks as well.I noticed them at the rear ends of Downtown Crossing and Tufts Medical Center yesterday. Could be a stopping point when running wrong-rail.
Gerry6309 wrote:Could be a stopping point when running wrong-rail.Saw one at the north end of the southbound platform at State today. It lined up with the cab window at the rear of the train. I'm almost inclined to suspect they're installing a screen for running wrong-iron or for short turning. It would certainly be necessary in some cases with some of the ever-so-gently curved platforms downtown.
StefanW wrote:...the yellow arrow tape markers could be used to calibrate / test the video surveillance.However if the arrows are also on above-ground stations that blows that theory also... unless there are general-purpose security cameras also above ground...?
Diverging Route wrote:A friend who is an Inspector on Rapid Transit confirms the marks are for a GPS survey that was recently done. Once in the tunnel, he says, they hadThe markers are reference points for old-fashioned surveying. GPS becomes unusable for surveying the instant you lose direct line-of-sight to GPS satellites.
a limited time for accurate surveying due to loss of GPS signal.