Safety Evaluation of Corner Clearance at Signalized Intersections

CHAPTER 2. OBJECTIVE

The objective of this research was to examine the safety effects of various corner clearances at signalized intersections in the State of California and the City of Charlotte, North Carolina, measured by changes in crash frequency. Target crash types included the following:

• Total—all crashes within 250 ft of intersection (all types and severities combined).
  
  
• Fatal and injury—all injury crashes within 250 ft of intersection fatal injury, incapacitating injury, non-capacitating injury, and possible injury.
  
  
• Rear-end—all crashes within 250 ft of intersection and the accident type coded as rear-end.
  
  
• Sideswipe—all crashes within 250 ft of intersection and the accident type coded as sideswipe.
  
  
• Right-angle—all crashes within 250 ft of intersection and the accident type coded as broadside or angle.
  
  
• Right and left turn—all crashes within 250 ft of intersection and the driver’s action prior to collision coded as turning right or turning left.
  
  
• Nighttime—all crashes within 250 ft of intersection and light condition coded as dusk, dark, and dawn.

A further objective was to address the following questions:

• Do effects vary by level of traffic volume on major and minor routes?
• Do effects vary by lane configuration of major and minor routes?
• Do effects vary by posted speed limit on the major route?
• Do effects vary by median presence on the major route?<
• Do effects vary by presence of turning lanes on the major route?

The evaluation of overall effectiveness included the consideration of the removal of driveway costs and crash savings in terms of the B/C ratio.

Meeting these objectives placed some special requirements on the data collection and analysis tasks, including the need to do the following:

• Select a large enough sample size to detect, with statistical significance, what may be small changes in safety for some crash types.
  
  
• Identify appropriate study sites with varied corner clearances.
  
  
• Properly account for changes in safety due to differences in traffic volume and other factors unrelated to corner clearance.