[GRASSLIST:659] Drive time analysis in GRASS?

[Brian McEntire]

Hello folks,
  I am interested in using GRASS/GIS to draw 5 minute driving time or
driving distance contour lines around a point. I believe a good amount of
road information is available in either of these sources:

  1) National Highway Planning Network - "(NHPN) is a 1:100,000 scale
network database that contains line features representing just over
450,000 miles of current and planned highways in the U.S. The NHPN
consists of interstates, principal arterials, and rural minor arterials."
  [The file is available in ARC/INFO Interchange (.e00) format.]

  or 2) US Censes TIGER/Line 2k maps from the US Census


Does anyone know if a GRASS module has already been developed to 
implement this? Or if implementing this in GRASS is a good idea to begin 
with? I don't want to reinvent the wheel, but I haven't turned up any 
open source or low cost applications that can do this.

Thanks for any ideas!
  Brian