The SPF Manager Intersections (Beta) 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 the SPF manager to generate unique SPFs for their intersections based on the Optimal Fit function. Agencies with previously developed SPFs can use the SPF Manager 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 the SPF Manager to keep a running history of their SPFs and track how they have changed over time.

Intersection Selector

The Intersection Selector section of SPF Manager 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 use the column on the left to select the number of legs, and then the control type. With each click, the column on the right will display all Intersection Groupings that meet the selected grouping criteria. Users can then select the group to evaluate from the second column, and the results will be displayed in the SPF preview on the right side of the page.

(The Intersection Selector, with the 4 legs, stop sign Intersection Grouping selected.)

SPF Preview

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 4 Leg, Stop Sign Grouping.)

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. The colored plane indicates the expected crash rate for that Intersection Grouping. Users can click and drag to rotate the chart. Hovering over an intersection will reveal the X,Y,X data for that specific intersection.

(the Intersection Graph with the XYZ flyout for a specific intersection displayed.)

Edit Function

Administrators can also use the SPF Manager 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.)

Optimal Fit

The SPF Manager 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 segments 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.)

SPF History

SPF Manager allows administrators to track and view the history of their SPFs. This allows agencies to track the performance of their SPFs over time, and track historical changes to the function.

(The SPF History window, displaying a historical snapshot of the modifications made to the given function.)

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