Adjustments to drive time estimates

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02-25-2011 05:09 AM
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New Contributor
We estimate the drive time between each of 8.5 million U.S. residential locations and the nearest of any of 900+ service locations. From these estimates we calculate access statistics by planning region. We are using Network Analyst 9.3 and StreetMap Premium (not Advanced). We will soon be upgrading to 10.

Our regional planners and other colleagues are concerned that the drive time estimates are often too low, i.e. not real world. They want us to make adjustments for "in traffic" conditions, thus we are exploring StreetMap Premium Advanced (and weighing its advanced pricing.)

However, we are also being pressured to develop other kinds of adjustments, such as seasonal adjustments for icy roads, or "population density", or "geographic isolation". We don't entirely understand what such adjustments would entail and we are resisting them. Our current position is that we are in no position to improve on the drive times estimated by Network Analyst and StreetMap Premium. We cannot ground truth the entire U.S.

That said, we would like to be as informed as possible on the matter. Does anyone know of literature or white papers where others have evaluated adjustments to drive time other than rush hour adjustments? Thanks.
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>Our current position is that we are in no position to improve on the drive times estimated by >Network Analyst and StreetMap Premium.

The Streetmap product does have attribute parameters that will allow you to slow down or speed up categories of roads. So when you create an OD layer, you can bring up the properties of the layer and on the Attribute Parameters tab change the speed associated with the roads. For example if you think that 55 MPH are really going at 50, then change it to 50.

I know this is very coarse compared to the historic traffic data speed profiles but it does allow some capabilities.

If you move to 10, you can use the new scaled cost barriers (point, line and polygon) to change the travel times. For example if you have climate polygons that say where icy conditions impact the roads, you can bring in those polygons and scale them by say 30 percent to slow all traffic down in that region. Simillar stuff can be done with population density polygons. Generally speaking, one of the use case for this new functionality is to import weather conditions from a weather service and slow down things to provide some real time travel times.

Regards,

Jay Sandhu
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Jay, thanks for that excellent response. We were somewhat aware of the capabilities you describe. They would be particularly helpful for spatially focused areas and specific seasonal conditions. However, our task is to produce the best estimate of "average" drive time possible between 25.5 million pairs of points across the entire 50 states. (8.5 million residences and each of three different types of care location). I know of no across the board adjustments for year-around conditions or pop. density that can or should be made to improve the estimates coming from StreetMap Premium and Network Analyst. I'm looking for validation of my assumption that there are no magical adjustments, or for information about those adjustments.
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