CE 552 Lab 2 - Critical Accident Location Laboratory Background Throughout the semester students will be examining many factors contributing to the crashes on the highway systems. We will learn about human, vehicle, roadway and roadway environment that may increase the risks. We will also examine strategies that may be most effective in helping to minimize these risks. Since the financial resources to address the needs within the safety improvement programs are always less than desired the decision makers wish to allocate the resources to those areas that are most critical. State departments of transportation are continuously looking to prioritize their investment strategies that have the highest probability of success. The data below are accident data for 16 sections highway segments in the same roadway classification. The crashes, by type (fatal, injury, and property-damage only (PDO)) are tabulated for a 3 year period and the Millions of vehicle miles of travel were calculated over this time. Sect Fatal Injury PDO Total Travel ID Acc. Acc. Acc Acc. (M VMT) a 0 7 12 19 2.940 b 0 3 16 19 2.292 c 1 0 9 10 0.984 d 1 2 14 17 5.100 e 0 6 22 28 6.930 f 2 16 58 76 11.790 g 1 12 30 43 9.840 h 0 3 14 17 5.130 i 0 3 7 10 1.884 j 0 1 9 10 0.692 k 0 2 5 7 1.494 1 0 5 14 19 1.494 m 0 0 30 30 0.984 n 0 1 14 15 1.968 o 1 5 16 22 5.850 p 1 12 38 51 11.820 The analyses conducted in this laboratory can be most easily completed using simple spreadsheet functions and sorting routines. To assist the student with data entry an excel file can be taken from the CE 552 web page. 1. Use the data above to rank the sections and then identify the top 5 priority locations, for each of the following evaluation criteria. In each case, the poorest or most critical section should have a rank of 1. a. Total crash rate per 100 million vehicle miles of travel (100 M VMT) b. Fatal plus injury crashes per 100 M VMT c. Severity rate in which total severity for the section will be a weighted severity in which each fatal crash is 40 times the value of a property damage crash, and an injury is weighted as 10 times a Property damage crash. The severity rate (combined cost from all accident types) will again be expressed per 100 M VMT. d. Sum the ranks of each section from a, b, and c to create a combined value and pick the top five from this combination. The lowest possible sum would be 3, if the same section was always identified as the poorest. [Note: this is equivalent to combining the ranks by giving 1/3 weight to each of the rating schemes.] Present your final results of the 4 assessments in a single table showing the ranking for each segment under the scenarios. Also show the ranks if we had just ranked on the basis of total crashes on each of the segments. 2. Discuss your results. Consider the consistency in the rankings, consistency with what projects would have been selected had you just used total crashes instead of crash rates, and other points that are important to you. What ranking technique do you prefer? Why? 3. An economic assessment of safety benefits may use crash loss values similar to the following: Fatality - $3, 341,000 Major injury $231,000 Minor injury $46,000 Possible injury $25,000 Property damage only $2,500 In step 11.c above, we used “relative” severity ratings of 40 for fatals, 10 for injuries and 1 for PDO. Do a sensitivity analysis on just the Severity question (1.c.) using factors of 120 for fatals, 20 for injuries and 1 for PDOs. Compare the section rankings using these scales with your original severity rankings. How does this affect decisions of the safety engineer? 4. Use the critical Rate formula with a k value of 1.64 for the following: a) fatal + injury crashes combined (assume the statewide average crash rate = 90 per 100 MVMT for this road class) b) all crashes combined (assume the average rate = 525 per 100 MVMT) The critical rate is that rate above which a section might be considered to need improvement. 5. Were your top five projects from step one always considered critical in your “statistical evaluation”? 6. From an investment viewpoint, which projects would you undertake? 7. What information would you still want to have? 8. Identify at least three reasons why the safety engineer may not find it feasible or desirable to just keep moving down the list (fixing each location) of the “high priority locations” as projects are carried out throughout the year.
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