Trying to create Service Area drive times from speed limits with Network Analyst

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04-06-2011 03:10 PM
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I want to create a service area map using Network Analyst. I have the ESRI Street feature class set up in a Network Dataset, but I cannot figure out how to display the driving time polygons. I can only get it to display by distance (like 1000 meters from the facility). The Street feature class has speed limits listed for each street segment, but no time attributes. I assumed that the Network Analyst could calculate time from the speed automatically, but I cannot figure out how to get the extension to do this. Any pointers?

Thanks,
Krysta Houseknecht
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You will have to add a TravelTime attribute and then set it's "Evaluators" to a field with an expression such as:  [LENGTH] / [Speed] ) * 60
This assuming the length is in miles and the speed is in miles per hour. You can change this expression based on the units of length and speed in your data.

An example of setting a walk or pedestrian time is in Tutorial 2. Search for the word "PedestrianTime" at the following link to see how to set that up:

http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//00470000005v000000.htm


Jay Sandhu
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Thank you so much!
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I found that for visualization purposes it is alot faster to

1. Not Generate Polygons
2. Generate Lines
3. Symbolize the Lines Based on the Total Accumulated Costs

You end up with the same result, but it is a little more realistic because you aren't generating a drive time for an area inside a polygon.

Also, you can play around with the symbology more because instead of generating polygons at a limited set of intervals (e.g. 10 min, 20 min, etc) you generate the lines which have the exact time to get to that line. So you could have the same underlying data and make several visualizations off of it.
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There is a simple way to use driving time as impedance for network anslyst.

start EDIT in the editor extension tool bar.

1. add a new field of [miles] in the table, if you do not have this information.
2. add a new field of [speed] in the table, which is mile per hour in this case.

The values of miles and speed should be in the table.

3. add new field of [hour] in the table.
4. calculate travel time by right-clicking on the [hour] field head and select [calculate...]
5. write formulation in the query windows as "[miles]/[speed]"
6. When you set up the network analyst parameter, select [hour] as impedance
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