There are no Dudhsagar falls between Lonavala and Karjat. The Braganza route's challenges are different compared to those of the Bhor ghat route.
What these people are afraid of, is actually a fear shared by many outsiders too.
At...
more... the part where the railway tracks cross the falls, there is a severe space constraint. The track crosses the first level of the waterfall very close to a sudden drop. It will be extremely difficult to construct another bridge there without constructing some kind of earthwork to strengthen the area and provide a stable foundation for the bridge. This will most likely end up altering the waterfall area significantly, probably even eliminate the 2nd drop of the waterfall completely by providing some other safe channel for the water to flow.
As most rail fans would know, the Dudhsagar falls and the railway bridge crossing them, are well known to tourists and the location is quite famous. Any altering the falls can potentially ruin the beauty of this place and detract tourists.