PREPARE CLUSTER BUFFERS

Summary

Prepare Cluster Buffers generates dissolved ‘cluster’ buffer polygons for Buildings Intended for Human Occupancy (BIHOs) and qualifying areas/buildings based on groups of BIHOs and qualifying areas/buildings, respectively, whose individual buffer polygons overlap. When the Boundary Adjustment Method selected is Arc Method, the cluster buffers are intersected with the centerline to produce structure and site (qualifying area/building) cluster segments. When the Boundary Adjustment Method selected is Perpendicular/Parallel Method, the tool uses BIHO and qualifying area/building influence ranges to produce structure and site (qualifying area/building) cluster segments, extending the influence range segments along the centerline by the appropriate length. Prepare Cluster Buffers performs these operations in preparation for calculating Class 4 and ‘clustered’ Class 2 and Class 3 location ranges (per 49 CFR §192.5(c)), and Class 3 ranges due to the presence of qualifying areas/buildings (per 49 CFR §192.5(b)(3)(ii)).

Usage

Prepare Cluster Buffers input parameters are divided into three sections:

1. Inputs

Number of Structures to be Considered a Cluster – The Pipeline and Hazardous Materials Safety Administration (PHMSA) has never rigorously defined the term, ‘cluster,’ or the number of BIHOs that constitute a cluster. Based on the language of 49 CFR §192.5(c), Prepare Cluster Buffers interprets ‘cluster’ to mean a set of BIHOs whose 660-foot buffers overlap. (Similar logic is applied to sets of qualifying areas/buildings for the purposes of defining Class 3 ranges per 49 CFR §192.5(b)(3)(ii).) This parameter allows you to define the number of BIHO dwelling units that constitute a cluster. If the number of BIHO dwelling units in a cluster is less than your threshold value, the IGNORE_FLAG field value is set to ‘Y’ on the cluster buffer and the cluster is ignored for the purposes of calculating clustered class location ranges. If the number of dwelling units in the cluster equals or exceeds your threshold value, the IGNORE_FLAG field value for the cluster is set to ‘N’ and the cluster is used in calculating clustered class location ranges. The default value for this parameter is 1; G2-IS’ interpretation of 49 CFR §192.5(c) is that a single dwelling unit constitutes a cluster. We recommend you use the default value.
Percentage (%) for a Cluster to be Considered Class 4 – Per 49 CFR §192.5(b)(4), “A Class 4 location is any class location unit where buildings with four or more stories above ground are prevalent.” PHMSA has never rigorously defined the operative term, ‘prevalent.’ Prepare Cluster Buffers defines prevalence in terms of the relative proportion (percentage) of 4-story or higher buildings in a cluster of 4-story or higher buildings relative to the total number of BIHO features in such a cluster. This parameter allows you to define the threshold percentage of 4-story or higher BIHO features (i.e., building footprints, not dwelling units) in a cluster that requires a Class 4 location unit. For example, if your threshold value is 50% and the number of 4-story or higher BIHOs exceeds 50% of the total number of BIHOs in the cluster, the IGNORE_FLAG field value for the output Class 4 Cluster Segment record is set to ‘N’ and a Class 4 location unit results. If the percentage of 4-story or higher buildings in the cluster does not exceed the threshold percentage, the IGNORE_FLAG field value for the output Class 4 Cluster Segment record is set to ‘Y’ and a Class 4 location unit does not result.

2. Boundary Extension

Boundary Adjustment Method – Arc Method (also called radial arc method) calculates clustered Class Location unit ranges using cluster buffers; the clustered Class Location unit ends where the BIHO cluster buffer intersects the pipeline centerline. When this method is selected, the tool consumes as input your specified Structure Buffer Features input data.

Perpendicular/Parallel calculates clustered Class Location units by locating the bounding BIHO/qualifying area/building influence range features for the cluster, and then extending along the pipeline centerline from the endpoints of the bounding influence range features using the values of Extension Length From Last Structure in Cluster (Feet) or Extension Length From Last Qualifying Area in Cluster (Feet), as appropriate. When this method is selected, the tool consumes as input your specified Influence Range Features input data.

Structure Buffer Features – This tool requires as input the STRUCTURE_BUFFER features output by the Prepare Structure and Site Buffers and Segments tool. Unless otherwise specified, the tool defaults this parameter to the STRUCTURE_BUFFER feature class in your selected Gas HCA Tool project geodatabase.
Qualifying Area Features – For use in defining Class 3 Location units due to the presence of qualifying areas/buildings, this tool requires as input the QUALIFYING_AREA_BUFFER features output by the Prepare Structure and Site Buffers and Segments tool. Unless otherwise specified, the tool defaults this parameter to the QUALIFYING_AREA_BUFFER feature class in your selected Gas HCA Tool project geodatabase.
Influence Range Features – This tool requires as input the DOT_BIHO_INFLUENCE_RANGE features output by the Calculate Influence Ranges tool. Unless otherwise specified, the tool defaults this parameter to the DOT_BIHO_INFLUENCE_RANGE feature class in your selected Gas HCA Tool project geodatabase.

3. Outputs

Structure Cluster Buffer Features – Unless otherwise specified, the default destination for the output BIHO structure cluster features is the DOT_STRUCTURE_CLUSTERBUFFER feature class in your selected Gas HCA Tool project geodatabase.
Structure Cluster Segment Records – Unless otherwise specified, the default destination for the output BIHO structure cluster segment records is the DOT_STRUCTURE_CLUSTERSEGMENT table in your selected Gas HCA Tool project geodatabase.
Site Cluster Segment Records – Unless otherwise specified, the default destination for the output the output qualifying area/building cluster segment records is the DOT_SITE_CLUSTERSEGMENT table in your selected Gas HCA Tool project geodatabase.
Class 4 Cluster Segment Records – Unless otherwise specified, the default destination for the output Class 4 cluster buffer segment records is the DOT_CLASS4_CLUSTERSEGMENT table in your selected Gas HCA Tool project geodatabase.
Class 4 Cluster Buffer Features – Unless otherwise specified, the default destination for the output Class 4 cluster buffer features is the DOT_CLASS4_CLUSTERBUFFER feature class in your selected Gas HCA Tool project geodatabase.

In a typical Class Location analysis workflow, Prepare Cluster Buffers is run immediately after the Calculate Influence Ranges tool, and before the Generate Sliding Ranges tool.

Syntax

PrepareClusterTool_hcapy (project_database, cluster_tolerance, prevalent_ratio, boundary_method, {structure_buffer_layer}, {qualifying_area_buffer_layer}, {influencerange_layer}, {ir_stuctureorsiteid_field}, {ir_route_id_field}, {ir_begin_measure_field}, {ir_end_measure_field}, {structure_ext_length}, {qa_ext_length}, {structure_cluster_buffer}, {structure_cluster_table}, {site_cluster_table}, {class4_cluster_table}, {class4_cluster_buffer})

Parameter

Explanation

Data Type

project_database

Dialog Reference

Select a Gas HCA Tool project geodatabase created using the Initialize Database tool. The output from this tool is stored in this workspace.