How Merge Divided Roads works

About the Merge Divided Roads tool

The Merge Divided Roads tool merges road segments that are parallel along a significant distance into one center line.

Matched pairs of roads or lanes are merged if they are the same road class, trend generally parallel to one another, and are within the merge distance apart. The road class is specified by the Merge Field parameter. All nonmerged roads from the input collection are copied to the output feature class.

This tool is generally used to simplify a relatively large-scale road collection at a smaller scale, where it is appropriate to depict divided highways and boulevards as a single line. At medium scales, it may be preferable to retain divided roads as separate features. In this case, you can use the Resolve Road Conflicts tool instead to ensure that symbolized lanes are displayed without symbol conflicts. If both Resolve Road Conflicts and Merge Divided Roads tools will be run on the same collection of roads, it is advisable to run Merge Divided Roads first.

Data preparation considerations

This tool is optimized for the spatial relationships typically found in a road network. Unexpected results may be produced if the tool is used to process other themes. It is very important that the geometry of the input features is correctly established for the tool to maintain the relationship of the features as they coexist in a road collection. Take note of the following input data requirements and suggestions:


A warning is raised if the input features are not in a projected coordinate system. This tool relies on linear distance units, which will create unexpected results in an unprojected coordinate system. It is strongly suggested that you run this tool on data in a projected coordinate system to ensure valid results. An error is raised and the tool will not process if the coordinate system is missing or unknown.

Workflow considerations

This tool is generally most effective when used in conjunction with other generalization and graphic conflict resolution tools. Here are some tips to help you use these tools together with other layers and other tools in a workflow:

Partitioning large datasets

This tool acts contextually such that adjacent and connecting features are considered when determining the final state of each individual feature. Using a large amount of input data can exceed memory limitations. To avoid this limitation, consider enabling partitioning when running this tool by specifying a partition feature class in the Cartographic Partitions geoprocessing environment variable. Partitioning allows the tool to sequentially process the data in logical and manageable chunks. The input features delineated by each partition polygon is loaded into the tool, along with additional data from a buffer zone surrounding the partition. The additional data is considered as processing proceeds. This ensures that the resulting feature classes are seamless, and the states of features spanning across partition boundaries are consistent.

When processing the Merge Divided Roads tool by partition, the resulting roads from each partition are appended into the output feature class. The roads will be split at the partition edges. Where merged roads are created, they are snapped at a common node at the partition boundary. Every effort is made to ensure consistent results across partition boundaries, but it is possible that in geometrically complex or dense areas, there may be situations where a road is snapped to an incorrect road, or a road is merged in one partition but not when it crosses into another. By adding the additional fields to the input feature class outlined below (short or long integer), you can query and display potential issues. These fields will be present and populated in the output feature class.

When an input road feature exactly follows a partition boundary, for example, a road follows the county line and counties are the partition feature class, the road will appear twice in the output, once for each adjacent partition processed.

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