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CE 3500

CE 3500. Transportation Engineering Safety probability calculations April 15, 2011. ANNOUNCEMENTS. Exam on Thursday; check practice exams Last homework due Monday. Group presentations: Pick one of your three projects

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CE 3500

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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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