There are 2 short stretches between BYPL and Bellandur Road where the track runs right beside the main road. At these two places, the track cuts through some very dense residential/commercial areas too, so doubling will be a real challenge.
But the railways did show some foresight, and at the place where the track crosses the Outer ring road, the railway bridge was constructed in such a way that a second track can be added to it later.