Known issues

1. The structure of OS MRN turn restrictions, versus the way Esri turns are modelled, does currently generate one issue when building these restrictions into the network dataset. This is because one of the criteria constraining the definition of Esri turn restrictions is that the exterior edge of one turn restriction cannot be an interior edge of another. However, there are a small number of OS MRN turn restrictions that invalidate this criterion. This is a known drawback and, currently, there is no solution to this conflict. However, this issue is rare and likely more common within built up areas. Therefore, depending on the use case, it should not be a major impediment to the use of OS MRN within the Esri environment. For example, for an OS MRN dataset for the Cardiff area, this constraint affected 0.5% of turn restrictions. These turn restrictions will be omitted from the built network. Therefore, the built network may contain fewer turn restrictions than the turnfeatureclass it is provided with.

When building the network, any warnings will be recorded in a text file named BuildErrors, located in your system’s temporary folder. This file will detail any problematic turn restrictions along with the corresponding error messages. You can typically find the temp folder at: C:\Users\username\AppData\Local\Temp

Alternatively, by running 'Build Network (Network Analyst Tools)' using the ArcPro interface, a path to this text file will be provided.

1. A small number of OS MRN turn restrictions have a NULL value for their restriction attribute. This is because the restriction only applies to one of the more specific transport types (for example: HGVs, goods vehicles, buses, public service vehicles, abnormal loads or wide loads). The turn restriction type will instead be listed under the restriction attribute for the specific transport type (for example: restriction:hgv). Currently, the script omits these restrictions from the provided OS MRN data. However, it would be possible to create these transport type specific restrictions, if this was desired.

In addition, turn restrictions which have exemptions, for certain transport types, are still being included in the network. If this is reducing the effectiveness of routing for particular transport types (for example, bicycles), the script could be adjusted to acknowledge these exemptions.