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Creating a Travel Distance

December 29 2008 | 2 comments
Categories: ArcGIS Methods

I am trying to create a 20 minute travel distance zone on a standard Census tract shapefile Any suggestions as to how I might get started using 9.2.

Mapping Center Answer:

First, you don't produce travel distances directly from a census tract shapefile.  You'd need a road network dataset (not just a shapefile, but something that contains weightings for speed limits, impedences for traffic lights, and stop signs, etc., and potentially additional time of day impedence weightings).  Most network analysis software has a drive time buffer function that will create or select the lines in the network dataset that are within a given drive-time of a point you enter.  You can then use that selection or set of lines to select census tracts--I would calculate a new field on the census tract to indicate that the tracts are within a drive-time of X for point Z.  That would allow you to code multiple drivetimes and locations into the same census tract dataset--making the demographic analysis (that I would expect somebody might do later) easier.

How i did it posted by Frank Pondrom on Apr 15 2010 5:30PM
Using layers with a line street file, I classified the line segments representing the roads as local,collector,highway, Interstate etc. I then assigned the average speeds as 20, 30, 40 and 65 respectively. Using the formulas
tRAVEL tIME = LENGTH*(60/(sPEED lIMIT)I used the measure tool obtained the length and usingnan excel spreadsheet calculated the travel times for the road sections until I reach a road lenght from the center of the area of interest of 20 minutes.

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