Google Maps V3: Markers only on streets?

User should be able to place markers on a google map but only on stree开发者_开发问答ts. Is this possible?

Google is your friend:

http://econym.org.uk/gmap/snap.htm

The basics of the solution is to ask for directions from the marker to itself. Google will return directions via streets, which will happen to be a single point on the nearest street.

Update the marker location accordingly.