Here’s a question from an anonymous follower, who asks:

“Is it good or bad to depict lines under construction on subway maps?”

In my opinion, if the line is actually under construction, then it’s definitely a good thing to show it. It gets users acquainted with the new line before it opens and generates interest. How you show it is up to you – dashed lines are the usual way, although advances in printing mean that transparent or translucent lines are also being used.

If a line is currently being planned, then I don’t think it should be shown on the map – things could change during the planning process and this could confuse people.

However, a good map designer will always work at future-proofing his map, so that new lines can be added in the future without having to reconfigure what already exists. This is one of the reasons why the Washington, DC Metro map has lasted so long – it was planned from the beginning to show the current track layout. It was only once the Dulles extension began construction that the map needed a review, as that extension was not part of the original plan.

From my own experience, when I did my own redesign of the Boston “T” map earlier this year, I purposefully aligned the northern end of the Green Line at Lechmere with the Lowell commuter rail line to take into account the planned Green Line extension, which shares the same right of way as the Lowell line (see picture above). The current official map doesn’t do this and will need to be redrawn when (and if) the Green Line extension opens.