Spatial Join - join features to only one target

[faoiltiama]

I would like to make a spatial join and use every join feature only once.

Current Input

• Layer1 = Lines of road segments --> Target Features
• Layer2 = Point data of accidents --> Join Features
• Join Operation -->Join one to one
• Keep all target features --> check
• Match Option --> within a distance (25 Meters because the points are not perfectly accurate)

Wish

Spatial join should match every accident to one and only one road. Output should have a Join count with the number of accidents that happened on each road segment. Each accident should therefore be counted on the closest road segment.

Problem

The only thing that doesn't work until now is, that the accidents can be assigned to multiple road segments this way. How can I prevent this?

[DanPatterson]

Are you using 

Add Spatial Join (Data Management)—ArcGIS Pro | Documentation

which supports one-to-one

or 

Spatial Join (Analysis)—ArcGIS Pro | Documentation

which supports one-to-many

[faoiltiama]

I'm using the latter, Spatial Join (Analysis)

[JamesPoeschel]

You can create a script tool for this.
You can rename the variable names if you like, in my case I was joining crashes to roads.

Here are the parameters:

And here is the execution code:

import arcpy
import os

# Define inputs and outputs
crash_points = arcpy.GetParameterAsText(0)  # Input crash points
road_lines = arcpy.GetParameterAsText(1)    # Input road lines
output_feature_class = arcpy.GetParameterAsText(2)  # Output feature class
search_radius = arcpy.GetParameterAsText(3)  # Search radius (e.g., "500 Meters")
near_table = os.path.join("in_memory", "near_table")  # Temporary Near Table

try:
    # Step 1: Generate Near Table
    arcpy.AddMessage("Generating Near Table...")
    arcpy.GenerateNearTable_analysis(
        in_features=crash_points,
        near_features=road_lines,
        out_table=near_table,
        search_radius=search_radius,
        location="NO_LOCATION",
        angle="NO_ANGLE",
        closest="CLOSEST"  # Only find the single closest feature
    )

    # Step 2: Summarize crashes per road
    arcpy.AddMessage("Summarizing crashes per road...")
    summary_table = os.path.join("in_memory", "summary_table")
    arcpy.Statistics_analysis(
        in_table=near_table,
        out_table=summary_table,
        statistics_fields=[["IN_FID", "COUNT"]],
        case_field="NEAR_FID"
    )

    # Step 3: Add crash counts (Join_Count) to roads
    arcpy.AddMessage("Joining crash counts to roads...")
    arcpy.MakeFeatureLayer_management(road_lines, "road_lines_lyr")
    arcpy.AddJoin_management(
        in_layer_or_view="road_lines_lyr",
        in_field="OBJECTID",
        join_table=summary_table,
        join_field="NEAR_FID"
    )

    # Export joined features with crash counts
    arcpy.CopyFeatures_management("road_lines_lyr", output_feature_class)

    arcpy.AddMessage(f"Spatial join completed. Output saved to {output_feature_class}")

except Exception as e:
    arcpy.AddError(f"An error occurred: {e}")
    raise

 In my case, I only needed the join count per target feature. You may need to edit it if you need more information.