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Transportation Safety: Probability Calculations in Engineering

Explore safety modeling challenges and crash reduction strategies in transportation systems using probability calculations. Learn how to assess crash likelihood and estimate accident rates with Poisson processes.

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Transportation Safety: Probability Calculations in Engineering

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  1. CE 3500 Transportation Engineering Safety probability calculations April 15, 2011

  2. ANNOUNCEMENTS

  3. Exam on Thursday; check practice exams Last homework due Monday.

  4. Group presentations: • Pick one of your three projects • Put yourself in the position of an engineering firm describing your recommendations to a city or state DOT • Speaking can be divided up however a group wants • 15 minutes maximum • Will be on Monday, Wednesday, and Thursday the last week of class (no class Friday the 29th) • Sign up for slots on Monday

  5. Grading: • Presentations are worth 10 points towards the group assignments • 3 points for organization (does your presentation make sense to someone who hasn't spent weeks working on it, time limit, etc.) • 3 points for content (are you using technical/engineering language correctly) • 3 points for delivery (professionalism) • 1 point for providing comments on other groups' presentations

  6. REVIEW

  7. What challenges are faced in safety modeling? in making transportation systems safer?

  8. Lots of crashes this year! Install a raised median. We can conclude the median reduced crashes by this amount

  9. Lots of crashes this year! Install a raised median. We can conclude the median reduced crashes by this amount

  10. Lots of crashes this year! Install a raised median. This is the true effectiveness of the median

  11. Solution: Identify common trends you can use to link any roadway to the data (regression!) Calibration factor: adjust to local observations if data available Crash modification factors Safety performance function: Average number of crashes on a road of this type

  12. WHERE DO CMFs COME FROM?

  13. The CMF clearinghouse: http://www.cmfclearinghouse.org/

  14. SAFETY CALCULATIONS

  15. Let's say we have calculated the expected average crash frequency. How can we answer questions such as: What is the likelihood there will be a crash this year? What is the probability there will be fewer than three? Can I get an upper bound on the number of crashes I will see (with some confidence level)?

  16. Here we make the assumption of a Poisson process. (What does that imply?) For a Poisson process, the probability of seeing exactly x events in a time interval t is where l is the average rate of occurrence. For crash modeling, we use l= EACF

  17. Continuing last example with EACF = 25 crashes/year... what is the probability there will be no accidents in a year? exactly ten accident in a year? exactly twenty-five?

  18. What is the probability there will be no accidents in a month? exactly four accidents in a month?

  19. What is the probability there will be between 23 and 27 crashes this year? What is the probability there will be at least one crash this year?

  20. With 95% confidence, what is the highest number of accidents we would see in a month?

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