Positive Guidance Principles

1. Positive Guidance Principles

2. Positive guidance concept • Provide drivers sufficient information about roadway design, operations, and potential hazards so they respond correctly and avoid crashes

3. CE 552 objectives related to PG • Identify problems Crash data, complaint files, site diagrams • Analyze driver tasks / performance On-site speed and driver studies • Assess the current information system Road safety audits a portion of this • Develop and evaluate improvements or modifications to the information system

4. Identify Problems Site diagram - zone definitions

5. Driving Task Components • Navigation • Guidance • Control • Class - what are the elements of each?

6. Driving Task: Navigation • Route selection • Distance to destination • Interchange / route change locations • Directions of roadways - i.e. general elements associated with trip planning

7. Driving task: Guidance Vehicle operator is in decision mode regarding lane placement, speed and more while considering existing: • Horizontal and vertical alignment • Roadway cross sections • Roadside obstacles • Traffic signage / controls • Traffic features - volume _ speeds

8. Driving Task : Control • Driver in reactionary mode • receives input from senses relating to vehicle handling. Examples: superelevation pavement texture speed / acceleration

9. Examine Guidance section:Traffic controls and human factors • D_R_D_R related to information or control signs (Detect, Recognize, Decide, React) • 1) D R D R distances • 2) Ability to read and recall information / driver visual acuity • 3) Primacy • 4) Expectancy • 5) Redundancy

10. Principle of Primacy Concept of primacy asserts that at any given moment, some information is more important than other information. • Control information is more important than guidance information • Guidance information is more important than navigation information. • Information about some hazards is more important than information about other hazards.

11. Principle of Primacy - Spreading Distribute information to driver to avoid peaks and valleys. peaks of information cause visual and memory overload. Distribute less important information to secondary position or valleys

12. Principle of Primacy - Spreading

13. Principle of Expectancy • Expectancy affects the perception and use of information. People expect certain things to appear and operate in certain ways. • Where do expect to find the light switch? Move switch up or down to turn light on? • Hot water on left or right? Turn clockwise or counter-clockwise to shut water off? (Tougher question )

14. Principle of Expectancy • Hot water on left or right? • Turn clockwise or counter-clockwise to shut water off? (Tougher question )

15. Principle of Expectancy How does this relate to highway safety design and controls? Exit ramps - _______ Color red - ________ Curve sign or turn sign - _______________ Chevron to indicate lane shift - ___________

16. Principle of Redundancy Recognize that different driver’s pick up cues in different ways AND short term memory is short, additional input is needed Example: Redundancy by _________________

17. Redundancy – earlier example But other issues may “trump” the redundancy card

18. Analysis zones in Positive Guidance

19. Analysis zones in Positive Guidance Basic analysis zones: Advance zone - distance before driver needs to be aware of hazard zone Approach zone - decision sight distance minus stopping sight distance Non-recovery zone - stopping sight distance Hazard zone - distance of hazard

20. Decision sight distance table

21. Decision sight distance tableAASHTO - 2001

22. Non – recovery zone Non – recovery zone is based on stopping sight distance (SSD). SSD = 1.47 V * t + V2 / (30( f +/- g)) What are the units for the above expression? What are appropriate values for t and f? [ g = grade in ft per ft ]