From BVI / BCT take a train to Dadar (WR). You will have to changeover from Dadar (WR) to Dadar CR (connected through FOB). From Dadar (CR) board a train to Kurla station (Local). From Kurla (Local) exit on the east side and hire a rickshaw for Kurla Terminus (LTT).
Some Technical points to note:
BVI and BCT are on opposite direction of Dadar (WR). BCT - DR - BVI
BVI...
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to Dadar (WR) 23 Kms (approx travel time 35-45 mins). Trains available at the interval of every 3-10 mins
BCT to Dadar (WR) 6 Kms (Approx travel time 8-10 mins). Trains available at the interval of every 3-5 mins
Dadar (CR) to Kurla (Local) (6-7 Kms) (Approx travel time 7-9 mins). Trains available at the interval of every 3-8 mins
Word of caution: Peak hrs traveling
During morning hours on wk days (Mon to Sat)
Trains are over crowded while traveling from Borivali to Dadar (WR).
During evening hours on wk days (Mon to Sat)
Trains are over crowded from BCT to Dadar (WR) and Dadar (CR) to Kurla.
It is advisable not to travel during the peak hours in the local train (especially if traveling with heavy luggage / senior citizen / kids). You might experience real hardships. Instead hire a pvt rickshaw / taxi to reach LTT from BCT / BVI. Keep sufficient time in hand in case you get stuck in traffic.
Alternately, Instead of boarding a connecting train for onward journey @ LTT you may opt for Thane / Kalyan (check if your train stops at any of these stations). There are direct local trains available from Dadar (CR) to Thane and Kalyan.