17.14 Speeding Countermeasures: Using Roadway Design and Traffic Control Elements to Address Speeding Problems

  • Designers can wield their knowledge of geometric design features to encourage motorists to make safer decisions about vehicle speed. Using consistent combinations of geometric elements that align with motorist expectations can reduce variability in speeds and improve speed consistency. Avoid sudden and significant changes in horizontal alignment, available sight distance, and curve radii because they increase the motorist’s workload and make mistakes and crashes more likely. Table 17.4 lists steps designers can take to ensure that road design and traffic control elements facilitate appropriate and safe speeds.
Table 17.4 Road Design and Traffic Control Strategies to Mitigate Speeding
Strategy Guideline
Control Speeds Through Consistent Combinations of Geometric Elements
  • Design road key elements to align with driver expectations:
    • Curve radius
    • Tangent length
    • Spiral length
    • Vertical grades and curves
    • Available sight distance
    • Cross-section features
Provide Adequate Change and Clearance Intervals at Signalized Intersections
  • Clearance intervals must account for:
    • Expected approach speeds
    • Operating speeds
    • Intersection width
    • Vehicle lengths
    • Driver characteristics (e.g., reaction time, braking)
Provide Protected Left Turns
  • At high-speed signalized intersections, implement protected-only signal phasing for left turns.
Improve Visibility
  • At high-speed signalized intersections, implement protected-only signal phasing for left turns.

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