[R-sig-Geo] Shortest network path distances

[Takatsugu Kobayashi]

Hi,

I would like to know if there are packages to compute shortest network 
path distances, something that can be down on TransCAD and ArcGIS 
network analyst. I have cencus tract centroids and network line 
shapefiles for 126 US urbanized areas. Basically, I would like to move 
the census tract centroids a bit to see how much it changes the shortest 
path distances.

If not possible, I guess I should program on ArcGIS using Python.

Thank you very much

Taka