With Google Maps now anyone can get step-by-step driving directions, Plan a trip with multiple stops, Check live traffic conditions (select cities) and now Drag 'n drop points to customize your route reports Ryan Sturgell and Barry Brumitt at the official Google Lat Long Blog.
You can customize our driving directions to follow the route of your choice. Simply click on the route, drag it around, and the purple line follows you. When you've found the route you want,
just "drop" it there. Google Maps will automatically create a waypoint to where you dragged your route. If you change your mind, just right- click the added location marker and select "Remove this destination" to reset your route.
Click here for their Youtube video.