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FHWA Home / Safety / Roadway Departure / Rumble Strips and Rumble Stripes

Rumble Strips and Rumble Stripes

Decision Support Guide for the Installation of Shoulder and Center Line Rumble Strips on Non-Freeways

Appendix B–Detailed Example Applications

Example Application 1 – Systemic Installation

An agency has identified 7,500 miles of rural, two-lane highways for retrofit installation of ELRS. The following information was identified for developing a B/C analysis of rumble strip implementation.

Assumptions:

  • ELRS cost per mile: 1,500 dollars per line.
  • Annual fatal and injury ROR crashes: 125 crashes.
  • Rumble strip life expectancy: 7 years.
  • CMF for ELRS for fatal and injury ROR crashes: 0.67.
    • CMF should be for fatal and injury ROR crashes.
    • CMF should be for ELRS if possible, SRS if no information available.
    • Use CMF 3394 from CMF Clearinghouse.
  • 2001 crash cost for fatal and injury crashes: 158,177 dollars.

Costs:

  • Installation cost = 1,500 dollars × 2 sides of the roadway = 3,000 dollars per mile.
  • Total cost = 3,000 dollars per mile × 7,500 miles = 22,500,000 dollars.
  • Capital Recovery Factor = ((1 + 0.07)7 - 1)/(0.07 × (1 + 0.07)7) = 5.39.
  • Annualized construction cost = 22,500,000/5.389 = 4,174,947 dollars.

Benefits:

  • Annual fatal and injury ROR crashes saved = 125 crashes × (1 – 0.67) = 41.25 crashes.
  • 2015 Crash Cost = 158,177 dollars × 2.47 = 390,697.20 dollars per crash.
  • Annual benefit from crashes saved = 41.25 crashes × 390,697.20 = 16,116,259 dollars.

B/C Ratio:

  • B/C ratio = 16,116,259/4,174,947 = 3.86.

Results:

  • Annual fatal and injury ROR crashes reduced: 41.25.
  • 2015 crash cost for fatal and injury crashes: 390,697.20 dollars.
  • Annualized construction cost: 4,174,947 dollars.
  • Annual benefit from crashes saved: 16,116,259 dollars.
  • B/C ratio: 3.86.

The results indicate that while the targeted facilities experience an average 0.017 fatal and injury ROR crashes per mile, the installation is economically justified. The analysis indicates that approximately 41 fatal and injury ROR crashes would be reduced per year.

Example Application 2 – High Crash Corridor Installation

For a 2.5-mile section of rural, two-lane highway, an analyst identified the following information from a roadway inventory, crash database, and safety performance function:

  • AADT 5,500.
  • 2012 ROR Crashes: 8 Observed, 3.67 Predicted.
    • Predicted crashes from SPF for rural, two-lane highways.
    • In this example, SPF is assumed to be for ROR crashes.
    • Crashes/year = 5,500 × 2.5 × 365 × 10-6 × e(-0.312) = 3.67.
    • Overdispersion parameter = 0.236 / L = 0.236 / 2.5 = 0.0944.
  • 2013 ROR Crashes: 7 Observed, 3.67 Predicted.
  • 2014 ROR Crashes: 9 Observed, 3.67 Predicted.
  • Percent fatal and injury ROR crashes: 50 percent.

The analyst is considering implementing CLRS and SRS in combination, for which the CMF Clearinghouse indicates the CMF to be 0.70. Other given information include the following:

  • 2001 crash cost for fatal and injury crashes: 158,177 dollars.
  • 2001 crash cost for property damage only crashes: 7,428 dollars.
  • Installation cost: 1,500 dollars per mile.
  • Rumble strip life expectancy: 7 years.

Expected Number of Crashes:

  • Observed crash frequency = 8 + 7 + 9 = 24 crashes / 3 years = 8 crashes/year.
  • Annual correction factor = 1.0 for each year.
  • The weighted adjustment, w = 1 / (1 + 0.0944 × 11.01) = 0.49.
  • The EB adjusted expected average crash frequency for year 1 = 0.49 × 3.67 + (1 – 0.49). × 24/3 = 5.88 crashes
  • The excess expected average crash frequency = 5.88 – 3.67 = 2.21 crashes/year

This identifies that the corridor is a candidate for treatment for excess ROR crashes. The analyst determines that CLRS and SRS are candidate countermeasures and examines them further.

Costs:

  • Installation cost = 1,500 dollars × 2 edge lines + center line = 4,500 dollars per mile.
  • Capital Recovery Factor = ((1 + 0.07)7 - 1)/(0.07 × (1 + 0.07)7) = 5.39.
  • Annualized construction cost = 4,500/5.389 = 835 dollars per mile.

Benefits:

  • Annual ROR crashes saved = 5.88 crashes/year × (1 – 0.70) = 1.76 crashes/year.
  • Annual ROR crashes saved per mile = 1.76 / 2.5 = 0.70 crashes per mile.
  • Average crash cost = 158,177 × 0.50 + 7,428 × 0.50 = 82,803 dollars.
  • 2015 Crash Cost = 82,803 dollars × 2.47 = 204,522 dollars per crash.
  • Annual benefit from crashes saved = 0.70 crashes × 204,522 = 143,984 dollars.

B/C Ratio:

  • B/C ratio = 143,984 / 835 = 172.4.

Results:

  • Expected number of ROR crashes: 5.88 crashes/year.
  • Excess expected ROR crashes: 2.21 crashes/year = candidate for CLRS and SRS.
  • Annual crashes reduced per mile: 0.70 crashes/mile.
  • 2015 crash cost for fatal and injury crashes: 204,522 dollars per crash.
  • Annualized construction cost: 835 dollars per mile.
  • Annual benefits: 143,984 dollars.
  • B/C ratio: 172.4.

The upper 95-percentile estimate of the CMF is 0.79, resulting in a reduction of 0.49 ROR crashes per mi per year. The annualized benefit is calculated to be 101,018 dollars per mile. The resulting B/C ratio is 121.0, indicating that even a conservative estimate of the reduction results in a highly cost-effect solution.

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Page last modified on December 22, 2016
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