Roadside Safety Design Fall 2017 Most of the Material taken from: Roadside Design Guide (2011) published by AAHSTO

History of Roadside Safety 1940s and 50s Most highway design components established here: horizontal alignment, vertical alignment, etc. 1960s Roadside safety design started to be discussed here 1970s Roadside safety design incorporated into highway projects 1970s - now National guidelines and substantial amount of research conducted on roadside safety design

Forgiving Highway Concept Driver Fatigue Excessive Speed Driving Under the Influence Crash Avoidance Roadway Conditions Vehicle Failure Poor Visibility

Forgiving Highway Concept 1. Remove obstacle 2. Redesign obstacle 3. Relocate obstacle 4. Use breakaway devices 5. Shield obstacle 6. Delineate obstacle

Crash Testing Cannot duplicate every roadside condition Provides an acceptable level of performance under normalized conditions NCHRP Report 350 provides recommendations for testing and evaluating the performance of roadside devices: A basis for comparison of impact performance merits of candidate safety features Guidance for safety manufacturers A basis for the formulation of safety feature performance specifications

Crash Testing Guidelines: Vehicle mass, speed, approach angle, and point on the safety feature to hit Test vehicle: passenger cars, ¾-ton pickup, tractor- trailer Impact speed: 20 to 60 mph Angle 0 to 25 degrees

Crash Characteristics First Harmful Event Fixed Object Fatalities (FARS)

Crash Characteristics

Roadside Topography Clear-zone concept: provide a traversable and unobstructed roadside area adjacent to the traveled way Dependent on design speed and vehicular traffic Roadside design affected by horizontal alignment Geometry: Foreslope Backslope Transversable slope (used in median)

Roadside Topography Clear Zone: Area located between the edge-of-travel way and the location of fixed objects (trees, posts, etc.)

Roadside Topography Foreslope 1V:4H or flatter: Recoverable 1V:4H – 1V:3H: Non-Recoverable <1V:3H: Critical (barrier needed see Chapter 5)

Roadside Topography Backslope

Roadside Topography Drainage Channel

Roadside Topography

Roadside Topography

Roadside Topography Traversable slope

Roadside Topography Traversable slope

Roadside Topography

Roadside Topography Adjustment for horizontal curves: Table 3.2 provides adjustment factors as a function of radius and design speed. These values are only needed if the site has been experienced safety problems (e.g., run-off-the-road crashes) See overhead.

Roadside Topography Adjustment for horizontal curves:

Drainage Channel Design Roadside Topography Drainage Channel Design Acceptable only for the following characteristics: Restrictive ROW Resurfacing, Restoration or rehabilitation (3R) projects Rugged terrain Low Volume Roads If not, you need a barrier

Roadside Topography Gradual design

Roadside Support Structures Sign Supports Traffic Signal Supports Luminary Poles Utility Poles Callboxes Trees Many are now designed breakaway supports

SLIP BASED SYSTEMS

SLIP BASED SYSTEMS

Roadside Barriers Used to shield and protect obstacles that cannot be removed (person-made or natural) A barrier becomes itself an obstacle Hence, the way the barriers are designed will significantly affect the risk of injuries when they are hit by a vehicle (i.e., this is why they are tested). There exist several types of barriers: Rigid: Jersey, Single slope, etc. Semi-Rigid: Box-beam, Steel-Backed Timber Flexible: W-beam, Three-stand cable The type of barriers selected is governed by the initial costs, repair/maintenance costs, risk of injuries, etc.

Warrant for embankment ROADSIDE BARRIERS Warrant for embankment

Warrants for non-transferable terrain and objects ROADSIDE BARRIERS Warrants for non-transferable terrain and objects

Example Design based on Speed, Volume, Slope Geometry ROADSIDE BARRIERS Example Design based on Speed, Volume, Slope Geometry

Definition of roadside barriers

BARRIER PLACEMENT Lateral Offset (def’d as “shy line offset”) Depends on speed Shy line offset not so critical for long runs of railing (as long as the barrier was introduced at or beyond the shy line offset) Terrain Effects Best results will occur when all four wheels are on the ground and the suspension is not compressed nor extended Flare Rate The rate between the end of the barrier and bridge railing Can affect how the vehicle will be redirected into traffic Length of need This the length needed to shield an object

ROADSIDE BARRIERS Shy Line Offset Shy-line offset: Distance between objects and barriers.

ROADSIDE BARRIERS Deflection Distance

ROADSIDE BARRIERS Terrain Effects

ROADSIDE BARRIERS Terrain Effects

ROADSIDE BARRIERS End Treatments Dependent on the type of barrier: w-beam, cable, concrete, metal (rigid) Energy versus non-energy-absorbing Flared versus tangent Site grading Advanced grading (no less than 1:10) Adjacent grading

ROADSIDE BARRIERS End Treatments

MEDIAN BARRIERS Suggested Guidelines

Suggested Guidelines: End Treatments MEDIAN BARRIERS Suggested Guidelines: End Treatments

MEDIAN BARRIERS Three-Stand Cable

MEDIAN BARRIERS Box-Beam Barrier

MEDIAN BARRIERS Strong Post W-Beam

MEDIAN BARRIERS Barrier Placement

ROADSIDE BARRIERS Barrier Placement

ROADSIDE SAFETY ANALYSIS PROGRAM Program used to perform a cost-benefit analysis of roadside conditions Four modules: Encroachment Crash Prediction Severity Prediction Benefit-Cost Currently being completely revised (Hence, won’t spend a lot time on this).

RSAP -Issues Only good for roadside devices (no rollover, crossover collisions, etc.) Long computation times (simulation) Multiple solutions Encroachment algorithm developed 30 years ago Vehicle path linear Lateral encroachment distributions (simplistic model) Crash Severity (highly variable)