time and length impedances

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11-08-2013 06:03 AM
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New Contributor III
Hello,

I built a network data set and then activated global turns. I was interested that no "Reverse" turns were possible (like between roads that form an angle smaller than 30º for example) so I applied a very high penalty for reverse turns. But when I calculate a route I see that still the slowest (but shortest) route is generated. For example, the final route (with a reverse turn case) will have 2000 minutes of drive time (because of the turns penalty) while if a put a barrier to force the route to take other roads in order to avoid the reverse turn, the alternative route is much faster, like 4-5 minutes (lack of penalties). But still the slowest route is chosen, despite the penalty!

In the properties window I have selected "minutes" as impedance. I even deleted the "Length" attribute from the network dataset. The are no other restrictions like oneway or so and roads are perfectly snapped. Do you know what is happening?

Thank you very much,

Bogdan
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New Contributor III
Related to this, I guess the question is: how can be the length impedance totally disregarded in NA?
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New Contributor
Well, as far as I am concerned, I give negative impedance (like -1 seconds) against Reverse turn, if I do not want Reverse turns. That restricts Reverse turn.

In Network Dataset, under Attribute tab, when you add an attribute, there is an option to make an attribute "Use by default". You have to check the check box located at the Add Attribute dialog box, so that the attribute acts by default. Generally, the time-related cost attribute like Minutes, (also Oneway, Hierarchy) are made to be used by default; while length related cost-attribute like Meters, Length, Miles, etc are not made to be used by default. Whether an attribute is being used by default or not, you will be able to know by seeing a small blue-coloured D mark against that attribute. Under such circumstances, the shortest route will be calculated based on time-related cost attribute.

Koushik Paul
India
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New Contributor III
Paul,

Thank you very much the reply. However, it does not seem to work for me. I have made minutes attribute to be used by default. Length attribute is not used by default. Still nothing. I am modeling my turns in the following way: on the minutes attribute I go to the default values, I choose turns and then Global Turn Delay. If I open the global turn delay window I get a list of possible turn categories and the penalties that can be assigned. I load the AllNetworkGlobal...etc.xml file from the ArcGIS installation folder so I make sure that ALL the combinations are visible. I apply the penalties for my road categories there.
I does not work...still the route solver would chose the shortest route over the quickest...I mention also that all the roads are in the same category with the same hierarchy obviously.

I tried to put -1 to all reverse turns but this doesn't  change anything. Reverse turns are still possible and apart from this, total time is not affected in any way. Where exactly do you put -1 to reverse turns? In which window?

I don't know really what's happening but getting very disappointed with NA.
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New Contributor III
Other interesting thing:

If I put a lot of penalties for the reverse turns and activate use start time option, the following happens:

1. The route solver chooses the route including the reverse turn
1. Because on high penalties the route has a duration (total_minutes) of 160 minutes
2. On the route properties I see that it lasts from 08:00 to 08:13.

How is this possible?
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New Contributor
Before hitting the Solve button, go to Network Analyst window. Click the Route Properties button next to the Route layer in the Network Analyst window. This will bring up Layer Properties dialog box. Click Analysis Settings tab. Select impedance as Minutes.

   Are you using Turn Feature Class in Network Dataset and does that Turn Feature class has unrestricted Reverse turns? Just go to Network Dataset Properties dialog box, click turn tab and check whether a Turn Feature Class is present along with <Global Turns>. Uncheck the turn feature class.



Koushik Paul
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New Contributor III
In my route properties I had always "Minutes" impedance activated. And there is no other turn feature class present, just the global turns.
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Esri Regular Contributor
Can you post a picture of your route on one of these "reverse" turns? Perhaps their are divided highways and there may be two left or two right turns at the location.

It is also likely that this is the only possible route and so it is taking the high penalty to get there. This can happen due to other restrictions or disconnected edges in the network.

Jay Sandhu
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