Network Analyst - Restrictions and Hierarchies

[TonySalomone]

Hi all,

I am creating a pedestrian network dataset and want to incorporate restrictions (lack of crosswalks, lack of ramps, etc, perhaps speed limit) and hierarchies (likely speed limits and other features).  I am wondering if all that is required is a binary coding method like 1, 0 (1 being the restricted segment) or if it can be on a scale of 1, 3, 5.  If the latter, would 1 be more or less restricted or lower on the hierarchy than a 3 and 5?) 

Any help would be great.  Thank you!

Tony

[JaySandhu]

In hierarchy, lower number means higher level road. So 1 would be interstate, 4 could be surface roads.

However, since you are putting together a pedestrian network, do not add a hierarchy. That is only useful for long distance, cross-country routes. For small walk/transit routes you are looking at a few miles of travel and hierarchy will be of no benefit.

Jay Sandhu

[TonySalomone]

Thanks for the response, Jay.  I see what you mean.  I tried different hierarchies with my dataset but really didn't see any changes in the resulting routes!  I do have several features that I can add as restrictions however.  I built the dataset with just one restriction (unmarked crosswalks) and using this definitely resulted in different routes.  Am I correct in thinking that restrictions are coding as binary (yes or no, or rather with an integer of 1 or 0?)   If so, do I need to add a new field for each type of restriction and turn them all on prior to solving the route?  I plan to add umarked crossings, "no ped xing" signs, uncontrolled intersections and the like as restrictions. 

I noticed that restrictions have parameters to choose from as well (prohibited, avoid:high, prefer:high, etc).  Do these act as hierarchies?

Thanks again for the response!

Tony

[JaySandhu · Accepted solution]

In your source feature class, you can code the restrictions in what ever scheme you like, for example, 0 or 1, Y or N, etc. When you start to add the restriction attributs in the Network Dataset create wizard, you can figure out how best to assign these fields to the restriction attribute. The restrictions can be prohibit, avoid and prefer. Please do not confuse these with hierarchy. Avoid means to avoid the road but use it if there is no other choice. A prefer road would be like a pedestrian friendly road that you want to use rather than avoid. You can read more about the restrictions here:
http://resources.arcgis.com/en/help/main/10.1/index.html#//00470000000m000000

You can also look at the tutorial datasets: Paris, San Diego and San Francisco and see how they have set up the restrictions.

Jay Sandhu

[TonySalomone]

Hi Jay,

Your advice was extremely helpful!  Restrictions were definitely the way to go for shorter, bike/ped trips (rather than hierarchy).  I am wondering if creating and adding a turn feature class is necessary for this work.  Would going into the Global Turn Delay Evaluator be necessary?  The only Cost feature I added was feet.  I didn't add an additional one for minutes. 

I guess I am asking is what is the purpose of the Global Turn Delay Evaluator and turn feature classes?  I've been using Network Analyst for a few years now and never saw the need. 

Thanks again for your help!

Tony

[JaySandhu]

Turn features can be used to add penalities or restrictions at turns. For example at some busy intersection, a left turn may take 30 seconds but a right turn could be just 5 seconds. In many places, a left turn or a u-turn may be prohibited.
Global turn delays can be used to automatically penalize turns without adding individual turn features at some intersections. For example, all u-turns could be set to take 20 seconds.

These kind of restirctions may not make sense for general pedestrian routes if you are using any travel time attributes. You can always add one based on average walk speed like 3 miles per hour IF you need to account for crossing busy streets, etc.
Some more info here:
http://resources.arcgis.com/en/help/main/10.1/index.html#/Turns_in_the_network_dataset/00470000000p0...

Regards,
Jay Sandhu

[TonySalomone]

Thanks, Jay. So I guess the turn feature class is useful when the network needs to account for additional lengths. Meaning, the actual movement of a vehicle turning left from one street to another needs to be accounted for, right? 

My network actually represents the linear features a pedestrian would use. I buffered the street centerline to creste sidewalks and crosswalks so there's four nodes at each intersection which was a sweet way to go. I am assuming that the inclusion of a crosswalk feature is adding to the "cost" parameter so the turn evaluator is a little redundant in my case. Though I do still see value if I were to include a temporal element.

Any additional thoughts would be awesome. Thanks so much!

Best,

Tony