Predictive Analysis Intersections application facilitates creating, managing, evaluating, and updating your agency’s Safety Performance Functions (SPFs) in an easily accessible interface. Agencies that have not yet developed SPFs can use Predictive Analysis to generate unique SPFs for their intersections based on the Optimal Fit function. Agencies with previously developed SPFs can use Predictive Analysis to evaluate the performance of their SPFs for each intersection sub-type, and make any modifications as needed to improve their performance. Additionally, all agencies can use Predictive Analysis to keep a running history of their SPFs and track how they have changed over time.
The Intersection Selector section of Predictive Analysis allows users to search for and select which Intersection type they would like to evaluate. All intersections are grouped according to the number of legs, and the intersection control type. Users can select the intersection characteristics from the dropdown to display all intersections of that type.
The Intersection selector dropdown
Once the user has selected the Intersection Grouping to evaluate, the SPF preview will display the actual Safety Performance Function, and the date on which it was last modified. Administrators will also have the ability to edit the Function and view the history of the SPF. This can be used to evaluate the effectiveness of any updates or changes to the Function.
The SPF Preview window displaying the results of the selected Intersection type.
If no Function is currently defined, administrators will be prompted to set the Function to the Optimal Fit, which is Numetric’s recommended SPF for that Intersection Grouping (for more detail on the Optimal Fit feature, see the Optimal Fit section of this article). Alternatively, administrators can edit the Function to enter their own SPF for the selected intersection.
The SPF Preview with no Function displayed.
When an Intersection Grouping with an operational Function is selected, users can see a 3-axis graph that plots each individual intersection that meets the grouping criteria. The X axis of the graph represents AADT of the intersection leg with a greater AADT, the Y axis of the graph represents the AADT of the intersection leg with a smaller AADT, and the Z axis represents the number of crashes. Users can click and drag to rotate the chart.
The Intersection Graph with the XYZ flyout for a specific intersection displayed.
The Details Sidebar displays metrics related to the selected Intersection Type: % of Roadway, % of Crashes, # of Intersections, and # of Intersections with AADT.
The % of Roadway metric indicates the percentage of the total statewide roadway that is represented in this Intersection Grouping. In the example below, 0% of the total statewide roadway system is represented by this Intersection Grouping.
The % of Crashes metric indicates the percentage of the total number of statewide crashes represented in this Intersection Grouping. In the example below, 0.24% of the number of statewide crashes are represented by this Intersection Grouping.
The # of Intersections metric indicates the number of intersections contained in this Intersection Grouping. In the example below, there are 694 intersections contained in this Intersection Grouping.
The # of Intersections with AADT metric indicates the number of Intersections contained in this Intersection Grouping for which we have AADT data available. In the example below, there are 703 Intersections in this Intersection Grouping for which we have AADT available.
The Detail Sidebar with the % of roadway, % of crashes, # of Intersections, and # of Intersections with AADT metrics displayed.
The Details to This allows agencies to track the performance of their SPFs over time, and track historical changes to the function.
Predictive Analysis also allows users to track and view the history of their SPFs. The Edit History & Comments section of the Details Sidebar displays the history of the actual SFP, and any comments that have been added. In this example, we can see that the Optimal Fit feature was used to define the SPF for this Intersection Grouping on the 16th of February, 2021.
The Details Sidebar displaying the current SPF, when it was defined, and who defined it.
Clicking on any of the points in the SPF Preview chart will highlight that intersection in the chart, and open a flyout for the selected intersection. This Intersection Flyout contains the intersection details, and summary of the selected intersection, as well as a Google Streetview thumbnail for the intersection.
Additionally, the selected intersection (point) will display the Expected Crashes per mile based Empirical Bayes calculations. Additionally, the Adjusted Performance Expectations section in the Intersection Flyout will display the expected crashes per mile, and expected crash rate, also based on Empirical Bayes calculations.
The flyout for a selected Intersection.
Administrators can also use Predictive Analysis to edit and revise individual Functions. These edits are tracked and allow for historical analysis - making it easy to see if the revisions to the Function are having the desired outcome.
The Edit Function window, with the user modifying a portion of the selected function.
The Predictive Analysis Intersections application provides its users with an optimal fit functionality, which can be used to generate an SPF based on Numetric’s Optimal Fit feature, which minimizes the average error between the annual crash rates for each of the Intersections and the SPF.
If an SPF is not entered for the selected Intersection Grouping, a button will display the option to Set to Optimal Fit. By clicking on this, administrators can set Numetrics Optimal Fit as the Function for that Intersection Grouping.
The Set to Optimal Fit button in the Function Preview window of a given Intersection Grouping.