Positive Guidance Principles

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

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

Identify Problems Site diagram - zone definitions

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

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

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

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

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

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 Control information is more important than guidance information Guidance information is more important than navigation information. Guidance information is more important than navigation information. Information about some hazards is more important than information about other hazards. Information about some hazards is more important than information about other hazards.

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

Principle of Primacy - Spreading

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

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

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 - ___________

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 _________________ Redundancy by _________________

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

Analysis zones in Positive Guidance

Basic analysis zones: Advance zone - distance before driver needs to be aware of hazard zone 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

Decision sight distance table

Decision sight distance table AASHTO

Non – recovery zone Non – recovery zone is based on stopping sight distance (SSD). SSD = 1.47 V * t + V 2 / (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 ] [ g = grade in ft per ft ]