Synthesis of Safety for Traffic Operations - Transports Canada

Synthesis of Safety for Traffic Operations March 2003
CHAPTER 3: INTERSECTION CONTROL
Signalization
Agent (1988)
Agent (1988) in a comprehensive study of 65 rural, high-speed intersections in Kentucky,
examined the effects of intersection control on crashes. The sites were selected to
provide a variety of traffic volumes, roadway geometrics, and traffic control. The 65
locations were comprised of 47 signalized sites, 15 minor street stop-controlled sites, and
3 all-direction stop-controlled intersections. Sixteen of the 18 unsignalized locations
were supplemented with intersection control beacons. Other forms of traffic control at
the study sites varied from site-to-site, ex., advance warning, signal phasing, stop lines,
transverse rumble strips, etc.
Using a cross-sectional analysis of the study sites, Agent reported the crash rates shown
in Table 3.1. The number of intersections exceeds 65, because some of the sites had
changes in intersection control during the study period.
TABLE 3.1: Crash Rates at Rural High-Speed Intersections in Kentucky
Control Type No. of Sites Crashes Crash rate (per MV) CMF*
Stop Sign 27 338 1.1 ---
Stop + Beacon 37 541 1.2 1.09
Traffic Signal 46 1290 1.2 1.09
* - Assuming a stop sign as the base condition.
Using a naïve before-after study of crash frequency, Agent also examined the effects of
changing intersection control on safety (Table 3.2).
TABLE 3.2: The Effect of Signalization of Crashes in Kentucky
Intersection Control
Crash rate
No. Sites
Before After
Before After
CMF
Stop sign Stop+Beacon 11 1.1 1.0 0.91
Stop sign
Traffic
Signal
16 1.3 1.8 1.38
Stop+Beacon
Traffic
Signal
20 1.4 1.1 0.79
Finally, Agent provides information on the severity of crashes at all locations, as shown
in Table 3.3.
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