1 / 33

NC Local Safety Partnership

NC Local Safety Partnership. Evaluation Methods. Workshop Roadmap. . . . . . Module Objective. Understand why evaluation is important Learn about the two basic kinds of evaluation methods Learn how to perform a simple before-after analysis. Safety Effectiveness Evaluation Basics.

jonco
Download Presentation

NC Local Safety Partnership

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. NC Local Safety Partnership Evaluation Methods

  2. Workshop Roadmap     

  3. Module Objective Understand why evaluation is important Learn about the two basic kinds of evaluation methods Learn how to perform a simple before-after analysis

  4. Safety Effectiveness Evaluation Basics How well has a treatment, project, or group of projects reduced crash frequency or severity? Evaluation

  5. Safety Effectiveness Evaluation Basics Why do safety effectiveness evaluations? Prove investment effectiveness Demonstrate program value to decision makers (accountability) Contribute new scientific knowledge Improve decisions Optimize future safety investments 11-5

  6. Results in Winston-Salem Result of 858 Low Cost Treatmentsin Winston-Salem over past 25 years

  7. Safety Effectiveness Evaluation Basics Goal – Measure true effect of a countermeasure We want to be sure that the observed change is due to the countermeasure alone What other factors could cause the change?

  8. Safety Effectiveness Evaluation Basics • What other factors could cause the change? • Other “treatments” at the same time (e.g., primary seat-belt law at the same time as adding a protected left-turn phase to intersections) • Changes in AADT • Regression to the mean • Underlying trends in crashes (e.g., economy-related changes) • Others • So how do we control for/discount these other “causes”?

  9. Two Basic Evaluation Study Designs • Before-after studies • Cross-sectional studies Choice of method is affected by: • Nature of treatment • Site type • Available data

  10. Before-After Study • Examines crash data before and after the treatment is installed • Types of before-after studies • Simple before-after study • Does not account for certain biases • Before-after study with reference/comparison groups • Accounts for changes in volumes and other factors

  11. Estimated average expected crash frequency without treatment Measured Simple Before-After Study ? Is this assumption realistic? TREATMENT ASSUME these are the crashes WITHOUT TREATMENT

  12. Expected average crash frequency without treatment Measured Before-After Study with Reference/Comparison Group TREATMENT Expected average crash count without treatment

  13. Before-After Study with Reference/Comparison Group Estimated average expected crash frequency without treatment Measured

  14. Cross-Sectional Study Compare crash data for sites with and without treatment over same time period

  15. Cross-Sectional Study • Why do a cross-sectional study? • Treatment installation dates unknown • Volumes and crash counts in before period unknown

  16. Evaluation Study Type Selection Guide

  17. Module 6 – Evaluation Methods Example SIMPLE Before-After Evaluation

  18. Example Simple Before-After Evaluation Traffic Signal Installation in Wake Co. NCDOT Safety Evaluation Unit conducted before-after evaluation Intersection of SR 1004 (East Garner Road) and SR 2555 (Auburn - Knightdale Road) Before: Two-way STOP-controlled After: Traffic signal (actuated)

  19. Example Simple Before-After Evaluation

  20. Example Simple Before-After Evaluation Signal installed in October 2003 Before period: Nov 1998 – Sept 2003 After period: Dec 2003 – Sept 2008

  21. Example Simple Before-After Evaluation

  22. Example Simple Before-After Evaluation

  23. Example Simple Before-After Evaluation

  24. Module 6 – Evaluation Methods ExampleS from Winston-Salem Evaluations

  25. Before and After Collision Diagrams

  26. Summary

  27. Graph of Poisson Distribution

  28. Take Away Messages Evaluation helps justify investments and improves decision making Pros and cons of different types of evaluation Steps for conducting simple before/after evaluation

More Related