PostGIS doesn't include a street routing algorithm. This is something that is a 
bit too complicated to provide a simple one-function-does-it-all solution - 
every road network is different, how do you deal with single-line/double-line, 
one-way/two-way, speed limits, turning restrictions at intersections, street 
addressing, etc - there is just too much to take into consideration, and not 
all road networks would have this information in the same format. 

What I'm trying to say is, something like this needs to be custom-tailored to 
the road network data that you are working with.

Chris

Quoting Ganesh Kuppuswamy <ganesh_kuppuswamy@csgsystems.com>:

> Hi,
>     I'm trying to calculate street level driving distance instead
> of straight line distance between two points. I have the street data.
> Does PostGIS have any functions which does this?  Or do i have to write
> my
> own?
> 
> Thanks
> 
> --
> Ganesh Kuppuswamy
> 303-200-3174
> 
> 
> 
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