Developing Safety Performance Function (SPF) and Crash Modification Factor (CMF) for Managed Lanes Separation Treatments

The goal of this project was to quantify the effects of managed lanes separation type on the safety performance of freeway facilities with managed lanes. The primary objective of the project was to develop quantitative measures that will be useful in comparing separation treatment alternatives for managed lanes. Following a comprehensive review of the state-of-practice, performance measures, and studies conducted on managed lanes by different agencies in the U.S., data were collected and processed for study sites in Florida, Texas, and Georgia. Data collected consisted of roadway characteristics, traffic volumes, roadway geometric cross-section of the managed lanes facilities, separation types (i.e., pylons and concrete barriers), operation strategies (i.e., nonreversible managed lanes, reversible managed lanes, etc.), and crashes for the years 2015–2019. Two facilities in Florida, 95 Express and 595 Express, were analyzed, based on available crash data. The study also included seven facilities in Texas and one facility in Georgia. Overall, 137.6 total miles of managed lanes facilities were included in the analysis. All facilities have at least one managed lane operating along the general-purpose lanes. The analysis included a combined total of 44,472 crashes that occurred on the general-purpose lanes and managed lanes during the study period. Safety performance functions (SPFs), crash modification factors (CMFs), and severity distribution functions (SDFs) were estimated. Separate crash models were developed by crash severity (i.e., fatal and injury (FI) and property damage only (PDO)) and collision type (i.e., single-vehicle (SV) and multi-vehicle (MV) crash), thus SV– FI, MV–FI, and SV–PDO, MV–PDO, to determine the predicted crash frequency for both non-reversible and reversible managed lanes facilities. Two managed lanes separation types were analyzed: tubular delineators (or tubular markers or pylons) and concrete barriers. For non-reversible managed lanes, results indicate that FI and PDO crashes decrease with greater separation widths between the managed lanes and the general-purpose lanes in the presence of pylons. On average, MV crashes (FI and PDO) increase by 21.2% for each additional managed lane. For reversible managed lanes, results indicate that SV–FI crashes decrease in the presence of concrete barriers as separation width increases between the managed lanes and the general-purpose lanes. MV–FI and MV–PDO crashes decrease by 29.4% and 34.7%, respectively, for each additional managed lane. The safety performance measures developed in this research could assist the Florida Department of Transportation (FDOT) as well as other transportation agencies when considering future managed lanes initiatives. In addition, the agencies could benefit from sample problems, spreadsheet application, managed lanes GIS inventory, and one-page summaries that were developed as part of this project.


  • English

Media Info

  • Media Type: Web
  • Edition: Final Report
  • Features: Appendices; Figures; References; Tables;
  • Pagination: 133p

Subject/Index Terms

Filing Info

  • Accession Number: 01893562
  • Record Type: Publication
  • Contract Numbers: BE975
  • Created Date: Sep 19 2023 9:27AM