This is common in modern systems with consistent lengths of trains and cars, consistent door placement, and a consistent stopping place.

But outdated systems like NYC's doesn't have consistent alignment when stopping, so it would be difficult for the train car doors to line up with the gaps in the fence (or wall/screen).

Here's how it should work in any modern system or system to be upgraded: http://blog.lareviewofbooks.org/wp-content/uploads/2015/12/K...