Alex Newmark at Transportation Nation reports NY MTA Tepidly Explores Platform Barriers After Subway Track Deaths … Again :
"Though the MTA would not cite a cost figure for installation, some proposals place barriers at over a million dollars per station. There are 468 stations."
Okay, lets use $468 million as our back-of-the-envelope price. The article also says:
"In 2012, 54 people have died on the tracks, either through falls, shoves or suicide."
Lets use $6 million as the value of a statistical life, consistent with US DOT. Let's assume there is a lifetime of 10 years, when the technology needs to be replaced. Let's assume no discounting. Let's assume it is 100% effective. The system will save 54*10=540 people for a value of $3,240,000,000 ($3.2 B), or a Benefit/Cost ratio of 6.9. I wish more transportation projects would get that.
We can make other assumptions, discounting, less than 100% effectiveness, higher prices fewer deaths per year and so on, which diminish this. There are additional benefits though (confidence in the system, fewer injuries, longer capital life, and so on) which would also need to be accounted for.
In the end, it sure seems like the B/C ratio would be well above 1.
The systems I have been in (like Kyoto below) that had them worked well. Of course retrofit is a more difficult issue, and this is New York, so the cost will inevitably be higher.