Statewide Curve Identification

Statewide Curve Identification - Procedure

Identify All Crashes Reported as Occurring on a Curve

Select all primary road crashes, reported by the officer in the field as occurring on a curve.

([Road_class]<=2) and (([Road_geome]=4) or ([Road_geome]=5) or ([Road_geome]=6)) Note: This selection set limits the primary roadways evaluated by identifying potential problem curves or continuous adjacent curves.

Assign "Curve" Crashes to Roadway Centerline

Using the [Shape] field, spatially join roadway centerline segments to the selected "curve" crashes.
Summarize the joined table using the [Road_link] (unique Base Record segment identifier). This yields a table containing a [Road_link] value and corresponding number of crashes occurring on the roadway segment, [Count].
Join the summary table, using [Road_link], to the roadway centerline theme.

Identify Curves and/or Curve Influence Areas

Visually inspect, systematically, each potential curve site. For example, this may be accomplished by sorting the summary table by [Count] or [Co].
Select the first record in the list and fit in the "View" window.
While displaying both the "curve" crashes and roadway centerline themes, place polygons around isolated curves, consecutive curves, and curve influence areas.

Note:
Given that crashes occurring on a curve often do not fall exactly on its cartographic representation, polygons are drawn in a manner as to include the crashes that should fall along this alignment.
If an intersection occurs along a curve, a portion of the intersection road may be included in the polygon.

The remaining steps, beginning with defining a curve theme, are essentially the same as our developed curve identification methodology, with two primary exceptions:

A spatial join between the curve polygons and crashes is utilized to assign a polygon identifier to each crash feature. Use of the polygon features, instead of linear curve features, was deemed appropriate given the likelihood of crashes not falling along the cartographic representation of the curve. Since the polygon identifier and curve identifier are the same for a given location, the ID value may still be used to assign and summarize crash data to the respective curves.
Crash rates, and rankings, are performed both with and without intersection crashes. Crashes are not limited to those defined as crashes having occurred on a curve.