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Georgia identified intersections as an emphasis area in the state’s Strategic Highway Safety Plan 2025-2030 (SHSP). In 2022, intersection-related crashes represented 21% of all roadway fatalities within the state. Based on data from AASHTOWare Safety (AS), crashes at signalized intersections resulted in 35% (194) of all intersection fatal crashes in 2022.

The Georgia Department of Transportation (GDOT) developed a process to target left-turn crashes at signalized intersections where protected left-turn signal phasing may be implemented. Safety performance measures for crash frequency, crash rate, and equivalent property damage only (ePDO) are used to direct a course of action. Figure 1 highlights the process on the following page.

The AASHTO Highway Safety Manual, 1st Edition (HSM1) includes a list of Crash Modification Factors (CMF) in Part D. The effects of modifying a left-turn phase at urban intersections to protected only operation will reduce left-turn crashes by 99% or a CMF of 0.01. Additionally, a study performed in 2008 by Harkey et al observed similar results (CMF ID 334). A more recent study by Asaduzzaman, M., R. Thapa, and J.A. Codjoe in 2022 found a CMF of 0.239, representing a 76.1% reduction, for left-turn fatal and all-injury crashes based on data from Louisiana (CMF 11163). While variations are present in existing research, protected left-turn lane safety treatment consistently shows a significant reduction in crashes involving a vehicle turning left.

Crash data from January 1, 2020, to December 31, 2024, was used to calculate safety performance measures for 7,918 signalized intersections. Intersection data received on September 19, 2025, was used for this analysis.

To target crashes where a protected left turn lane may reduce crashes, the “Protected Left Turn Evaluation Filter” was developed using the logic documented below.

Protected Left Turn Evaluation Filter Logic

With the filter applied, there are 70,217 crashes, including 244 fatal crashes and 2,120 suspected serious injury crashes, used in the analysis and results.
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Safety performance measures were calculated for all 7,918 signalized intersections. Total crashes, crash rate, and ePDO were calculated for each intersection using AASHTOWare Safety Advanced Network Screening. These values were used to develop the 75th and 95th percentiles by area type and GDOT District. The resulting percentiles identified the intersection tier for the evaluation of the protected left turn lane. Only the urban thresholds were used by GDOT District 7. Tables 1 and 2 contain the percentile thresholds, and Table 3 summarizes the number of intersections in each tier.

*District 7 thresholds were set to urban intersection values.

With the tiers for all intersections identified and available in AASHTOWare Safety, analysts can find an intersection's tier with the steps below:

1. Open the “Intersection - Protected Left Turn Lane Evaluation” project in Crash Query.

(The “Intersection - Protected Left Turn Lane Evaluation” project is located within the GDOT Templates category in Crash Query.)
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2. Users can also access the project by clicking the home icon in Crash Query and selecting the saved “Intersection - Protected Left Turn Lane Evaluation” in the GDOT Templates category.

(The Make a Copy button is located in the top-right corner of the screen in Crash Query.)

3. For reference, all criteria used to build the “Protected Left Turn Evaluation Filter” are included in the filter bar of the “Intersection - Protected Left Turn Lane Evaluation” saved query.
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(The filter bar in the “Intersection - Protected Left Turn Lane Evaluation” saved Query.)

4. Locate the intersection you want to evaluate either by zooming in on the map or using the map search function.
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​5. The purple layer defines the intersection. Hover your mouse over the purple intersection to display its tier level.
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(The purple layer is displayed at the intersection, with its tooltip visible.)
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6. Based on the Intersection Tier, use the Evaluation Process flow chart to identify next steps.
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7. To dive deeper into the crashes used in the analysis, scroll down in the flyout menu and click the Collision Diagram link. This will open the AASHTOWare Safety Collision Diagrams tool.

(The Collision Diagram link can be found by scrolling in the Intersection Flyout menu.)

8. In Collision Diagrams, add the “Protected Left Turn Evaluation Filter” to review crashes used in the analysis. Now, you can understand crash patterns and how to effectively deploy the protected left-turn lane phasing countermeasure.

(Add the “Protected Left Turn Evaluation Filter” to the Filter Bar in Collision Diagrams)