Investigate relationship between road pavement conditions and accidents in Pitt County, NC

Problem

The city of Greenville, NC wants to investigate the relationship between road pavement conditions and accidents in Pitt County in order to mitigate their occurrences. They also want to customize the ArcGIS Pro interface to streamline the Linear Referencing (LR) process.

Analysis Procedure

The ArcGIS Pro LR Tab is first created to consolidate the tools needed for this project. There are nine tools to be created in the tab, seven from the LR Tools, and two to be downloaded from Texas Department of Transportation. The accidents table, pavement rating table, routes feature classes, and boundaries shape files would be supplied by Pitt County. The attribute of the accidents table is the record of accidents and the attribute for the pavement table is the rating. The record of accidents is a point event and the pavement rating is a line event. In order to find out the relationship between the road pavement condition (rating) and the number of accidents, the equation of number of accidents ¸ length of road segment will be used for the specified rating. The two attributes have to be combined for each road segment and a new field added to calculate the length of road segment in miles. The output event table will have the rating at each accident point event.

At the start, the pavement rating threshold had to be specified. In this study, the rating threshold was 75. Both accidents and pavement tables were event tables and can be used by the Overlay Route Events tool. It was also important that the tables had the same route reference. However, the new field to calculate the length of road segment had to be added to the pavement event table before the Overlay Route Events tool was performed. The new field was added using New Field and Calculate Field using difference in start and end mile points. The Overlay Route Events tool was used to intersect the accident point events and the pavement line events and had to be implemented via Python due to difference in geometry of the events. As the event tables had a big dataset (3644 records in the accidents table and 557 in the pavement table), it was strategic to extract a small subset say Route 30000030 using Select by Attributes. After the Overlay, the number of accidents was counted in Route 30000030 for ratings <=75 and >75 and each number divided by the length of road segment of the same route ID. All event tables were displayed on the map using Make Route Event Layer, together with a route layer and city/county boundaries.

Workflow Diagram

Results

Application and Reflection

Linear referencing is used mostly for linear features such as networks, drainage, pipelines. Popular use of LR in routes such as carrier routes from USPS, hydrology in streams and catchment basins, traffic conditions in roads and highways.

Problem Description To create an event map on traffic conditions along roads and highways of North Carolina for year 2018 so NC Department of Transportation (NCDOT) can locate which roads and highways are heavily used. This will allow them to plan ahead for the surface maintenance schedule base on route usage.

Data Needed There are two key data used in the analysis: roads and highways route layer and the traffic route event layer. Both can be downloaded from the NCDOT GIS resources website. Both have shape fields of polylineM. The traffic route event contains the Annual Average Daily Traffic (AADT) for each route.

Analysis Procedures Both route layers have to export to event tables before they can be overlaid using Overlay Route Events. Both have the same Route Identifier, RouteID which is one of the parameters used in the Overlay tool. The Overlay tool will output a table where both sets of attributes, only the ones common to each other, are combined into a single event table. The common roads are the ones required maintenance by NCDOT. There are roads that are not under the maintenance of NCDOT, usually local roads. So, the output table will show AADT for each RouteID maintained by NCDOT. There are about 47,352 roads and highways segments maintained by NCDOT and the AADT reflects the number of traffic that ply along that route which is display in the attribute table for analysis use. To display the AADT on the map, the Overlay table has to be saved as a layer file.