# FT_MINUTES calculation

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03-25-2019 11:22 AM
New Contributor III

I am working with Esri's Custom Roads and Street Map Premium in ArcPro. I am having trouble understanding the FT_MINUTES and TF_MINUTES fields, how to calculate them, and exactly what they represent. If someone could provide me with some information that explains it I would greatly appreciate it. Also, since a lot of the attributes are in meters (including the coordinate system), but the modeling is done in MPH, I was hoping that someone could also provide information on the conversion process. Thank you so much!

5 Replies
Esri Contributor

Do you see a pdf file in the Custom Roads FGDB folder? for instance on my machine its file name is: StreetMap_Premium_Custom_Roads_ArcGIS_Pro23.pdf.

On the above pdf file at Page 19, I see the following:

• FT_MINUTES: From Traveling Time in Minutes
• TF_MINUTES: Toward Traveling Time in Minutes
MVP Emeritus

Which historically meant with or opposite to the direction of line digitizing, so be careful. It can't be tied to a destination since the road network needs to work with any origin-destination pairs.

New Contributor III

Thank you for the response. I have seen that explanation in the documentation. Can you tell me what formula I would use I populate these fields? I’m confused on if I need to use the shape length or meters field (which is calculated in geodesic units). And how to convert from meters to MPH to get to minutes. Any help would be greatly appreciated.

MVP Emeritus

You need the speed limit for the roads in order to convert the distance/length to a traversal time

Esri Contributor

[I'm updating my comment because I have better information now]

About the shape length, if your streets are in a Projected Coordinate System that preserves the DISTANCE property (see articles: 000006113, 000011356  ), feature class shape length would be good enough for your purpose. Obviously, geodesic measurement is better but because streets segments might be small so geodesic measurement and shape length  might be equal.

The Shape_Length field contains a projected planar distance for the given coordinate system (Web Mercator for the SMP Custom Roads data).  The Web Mercator projection does NOT preserve distances, so the Shape_Length field would NOT be a good choice to use as a measure of distance.  For this reason, it’s best to instead use the geodesic distance.  Regarding planar distance versus geodesic distance the difference between the two depends on the direction of travel of the segment (mostly north-south vs. mostly east-west) and how far away from the equator you are.

For the future, I still recommend consulting these two articles:  000006113, 000011356. And if you're calculating length, it's always a good idea to use a Projected Coordinate System that preserves Distance as discussed at  article: 000006113.

For the FT_MINUTES and TF_MINUTES calculations,  you can use the following formula:

Time = Distance / Speed

For the Conversion: Time in minute = [(distance in meter) / 1609.34]/[(speed in MPH)/60]