I moved to the Chicago area around a little over a year ago and this feature has been around at least that long.

It's also available by enabling the "Transit" layer under the "More..." button, and also the transit layer in the Maps application on Android (and presumably the iPhone).

It's an incredibly handy feature when you don't know the area and/or combined with the "Arrive By" option under Public Transit when getting directions.

I moved to Chicago three years ago, and it was around even then. The feature enabled me to quickly learn all of the routes.

Yes, very helpful but this feature isn't new at all.

Yes, but in a shockingly poor UI decision, if you click the X to banish the huge white balloon that covers a quarter of the map and obscures the el line you want to look at, the balloon does go away but it takes the route line with it! How perfectly ridiculous.