TrixBrix has just launched a tremendous series of narrow gauge tracks. Narrow Gauge tracks for the LEGO train system are two studs narrower than standard gauge tracks. This means, that narrow gauge sleepers are just 6 studs wide (instead of 8 for standard gauge tracks).
Curves are available in three different radii (R24, R36 and R48), straights come in different lengths (2, 4, 8 and 16 studs). Switches and crossings are also available.

A very cool feature is that the narrow gauge tracks can be combined with standard gauge tracks. This means, that you can enhance a standard gauge track by some rails and make it available for narrow gauge trains. Check out the following example:

Luckily, the TrixBrix guys send me description and images of the parts in advance, so I was able to integrate the parts in the TrixBrix Track Library for Bluebrick on time.
I recommend to try out the narrow gauge tracks with Bluebrick first, then buy the tracks on the TrixBrix online shop at trixbrix.eu.
Update for the library is available here.
This is a tremendous enhancement! Thanks for sharing this information and also for updating the track library so quickly!
Bob