Every city/town near state Border must have ISBT. 
Siwan - covers lucknow, Varanasi, Gorakhpur
Sasaram/Bhabua - covers prayagraj, varanasi, lucknow
Gaya - Covering jharkhand
Bhagalpur - covering bengal &amp; jharkhand
Motihari - Nepal
Purnia - North east and north bengal