I use such urls like:
http://maps.google.com/?saddr=546%206th%20Avenue,%20New%20York,%20NY%2010011%20(Sixth%20Avenue,%20New%20York)&daddr=W%20103rd%20St,%20New%2
Google Maps Javascript v3 and the Directions Web Service now has this capability as per : http://googlegeodevelopers.blogspot.in/2012/06/public-transit-routing-and-layer-now.html