In our inbox yesterday appeared a link to a TTC tender for consultant services, sent to us by Joe Clark (as these things tend to be). They're looking to hire someone to (emphasis ours) "provide professional architectural, engineering/design services and specialized transit services to perform the study concerning the installation of platform screen doors at 75 locations in 69 subway stations and in the six stations that will be constructed within the Spadina subway extension, as well as the documentation to allow the Commission to install a test installation in an agreed upon location."

Sigh. The installation of doors mediating the passage between subway platforms and trains is one of those sound-in-principle ideas that pops up every few years and is promptly shuffled back toward the bottom of the pile of TTC daydreams, somewhere below fare cards and above a commuter ferry service. Although many transit systems in Asia and a few in Europe use such doors, it is extremely unlikely that they will be installed on the TTC any time soon. (Even New York's MTA has apprehensions about introducing them on the new Second Avenue subway line.)

Instead of shelling out for a high-priced consultant to conduct a study, the TTC, as with most things, could save themselves a good deal of money by just asking Steve Munro. Torontoist happened to do just that at a TTC meeting in February, and here's why we won't be getting screen doors in the near future:

1) They're extremely expensive to install and maintain. Think about the rate at which elevators are currently being added to stations to make them accessible. Now imagine that each station had to have a construction project of at least ten times the scale that would be proportionally disruptive to its normal use. If the TTC had that kind of money, they'd improve service, expand the network, and maybe even implement a new payment system.

2) The TTC simply doesn't have the technology in place to perfectly align braking trains with specific points on the platform. Although operators are supposed to get as close to the red dot on the wall as possible, in practise there is considerable range within which trains can and do stop (and on rare occasions, they even overshoot the platform). For platform doors to work would require the TTC to create and install an entirely new system of (likely computerized) train controls and brakes.

3) "Everything mechanical on the TTC breaks down in a week. Imagine being on a train and the doors don't open." Perhaps we're being cynical, but consider what would happen if the ability to board and disembark from trains were as tenuous as any given escalator.

4) They would substantially interfere with the way that stations are ventilated. Since the opening of the system, the TTC has relied on incoming trains to push fresh air into the stations. (Although platform edge doors, unlike platform screen doors, do not reach the ceiling, the rush of air coming over a barrier would probably create its own set of problems.)

If you have an engineering degree and want to be the one to break this to the TTC, your first step is to head up to Yonge and Empress and hand over a $25 cheque, money order, or bank draft (but NO CASH) to pick up the bid documents. Here's who's done it already.

Video of the Tokyo Metro Namboku Line at Iidabashi Station by Kwitiaow. Photo of the Jubilee line at Westminster station, "the only London tube station with platform doors," by JohnSeb. With additional reporting from David Topping.