How do I build a network which can have time impedance from a data set which has road lengths and speed limits assigned?

[EllenWildig]

I'm trying to create a service area which shows locations 24 hours from a city. I have a roads dataset which already contained road lengths and to which I have assigned a new attribute, their speed in mph. However, when I build the network the only impedance option is distance. How do I create a dataset where time can be the impedance factor? Thanks

[MelindaMorang]

You have to add your own impedance attribute to the network and set up the "evaluators" correctly to calculate the travel time based on the road lengths and the speed limits.

Here are some documentation pages that might help you out:

- Exercise 1: Creating a network dataset—Help | ArcGIS Desktop 

- Understanding network attributes—Help | ArcGIS Desktop 

- Types of evaluators used by a network—Help | ArcGIS Desktop 

That said, unless you have a compelling reason to create your own network dataset in this manner, you might get better results more quickly by either purchasing a Streetmap Premium network dataset for  your area of interest or using Esri's ArcGIS Online routing services.  The data quality will likely be better, and it saves you a large amount of time in creating and debugging your own network dataset.

[EllenWildig]

Thanks for the info and the links, they really helped! Unfortunately my compelling reason is a uni project which needs a certain level of complexity, so making life deliberately harder for myself....

[DanPatterson_Retired]

certain fields are looked for during the construction of network... speed limit and segment length can be converted to time, which you can use if the appropriate field is in the source table... you can get as fancy or restrictive as you want by playing with the evalutators (see link above) and your turn restrictions