Combating Roadway Departures Roadside Safety Design

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Florida Combating Roadway Departures & Roadside Safety Design Workshop – Day 3

Combating Roadway Departures &

Roadside Safety Design

July 13/15/20/22, 2021Florida Department of Transportation

Tori BrinklySenior Safety EngineerFHWA Resource Center

[email protected]

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Workshop Agenda

DAY 1

Module 1: Introduction

Module 2: Keeping Vehicles on the Road

Module 3: Providing a Recovery Area

Day 1 Wrap‐up

DAY 2 –Any Questions?Questions from Day 1

Module 4: Roadside Devices

Module 5: Roadside Objects

Module 6: Urban Environments

Day 2 Wrap‐up

DAY 3

Questions from Day 2

Module 7: Intro to Barriers

Module 8: Flexible Barriers

Module 9: Semi‐Rigid Barriers

Module 10: Rigid Barriers

Day 3 Wrap‐up

DAY 4

Questions from Day 3

Module 11: End Treatments

Module 12: Crash Cushions

Module 13: Length of Need (LON)

Course Wrap‐up

Overarching Workshop Outcomes

• Describe the roadway departure crash problem.• Identify the practices and proven safety countermeasures tomitigate roadway departures.

• Identify roadside design strategies to optimize safety withinpractical limitations.

• Describe practices that improve the ability of drivers to stay intheir lane or regain control.

• Identify factors affecting the proper placement of roadsidehardware.

• Understand performance characteristics of different barriers andbarrier end treatments.

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Roadway Departure Objectives

1st - Keep vehicles on the road

2nd - Reduce the potential for crashes

3rd - Minimize the severity

• Curve Signing• Pavement Markings• Friction Treatments• Rumbles

• Shoulders• SafetyEdgeSM

• Center Line Buffer• Clear Zone• Traversable Slopes

• Breakaway Devices• Barriers

Day 3 Learning Outcomes

•Discuss general considerations for the use of barriers•Recognize currently acceptable barriers•Discuss the differences between the barrier systems

•Discuss placement considerations

3rd - Minimize the severity • Breakaway Devices• Barriers

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Module 7

Introduction to Barriers

RDG Chapter 5 & 6

•REMOVE the obstacle

•REDESIGN the obstacle for safe traversal•RELOCATE the obstacle•REDUCE severity (make breakaway)

•SHIELD the obstacle•DELINEATE the obstacle

RDG Page 1‐4

Roadside Obstacle Mitigation

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Roadside Barriers

Barriers are fixed objects that can result in injuries or fatalities when hit.

Source: FARS 2017-2019

Poles/ Sign Posts

Barriers955 fatality/yr

Other Fixed Objects

The most common barriers systems are:• W‐beam guardrail• Concrete barriers• Cable barriers

Barriers are 12% of Fixed Object Fatalities

Trees

•Roadside Barriers

•Median Barriers

•Bridge Railings

Barrier Context

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Flexible Systems

Weak Post W‐Beam

Generic Cable

High Tension Cable

Deflection can be over 5 feet

Strong Post W‐Beam

Semi-Rigid Systems

MGS (31”) W‐Beam

Deflection can be 2 ‐ 5 feet

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•All are Reinforced Concrete•Safety Shaped

−New Jersey Shape

− F‐Shape (Preferred)

•Single Slope•Vertical Wall

Rigid Systems

NJ Shape F‐Shape

Deflection can be 0 ‐ 1 foot

Barrier Comparison Video

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Simpson County

FHWA

Guidelines for Barriers

•Barrier must be less severe than the obstruction

•Economic analysis basis (B/C)

•The “Innocent Bystander”•Crash history

FHWA

Typical Barrier “Warrants”

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Typical Barrier “Warrants” – Bridge Piers

Typical Barrier “Warrants” – Large Culverts

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Typical Barrier “Warrants” – Sign Supports

Typical Barrier “Warrants” – Bodies of Water

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Typical Barrier “Warrants” - Embankment

Embankments – Comparative Risk

Basis for shielding embankment is

Comparative Risk: Slope risk vs. Barrier risk

RDG Figure 5‐1

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Head-On Crashes

NCHRP Report 500, Volume 4 Reported that only 4.2% of head‐on crashes

involved a passing vehicle.

“Warrants” for Median Barrier

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RDG Figure 6‐1

Median Width Guidelines

Florida Green Book

Table 3‐23 and Section E.6

•Traffic volumes & mix

•Median cross slope

•Crossover & crash history•Horizontal curvature•Proximity to interchange

Other Median Barrier Considerations

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Roadside Placement Considerations

•Obstacle OffsetBarrier DeflectionWorking WidthZone of Intrusion

•Placement on Slopes

•Other ConsiderationsUse of ShoulderFrequency of ImpactsLength of BarrierShy DistanceSoil Support

Dynamic Deflection – the maximum lateral displacement of the test article on the traffic side that occurs during the impact.

DynamicDeflection

Working Width – the distance between the barrier face before impact and the maximum lateral position of any major part of the system or the vehicle after impact.

Working Width

Dynamic Deflection/ Working Width

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Zone of Intrusion (ZOI) – the region measured above and behind the face of a barrier system where an impacting vehicle or any major part of the system may extend during an impact Working Width

Zone of Intrusion

Working Width – the distance between the barrier face before impact and the maximum lateral position of any major part of the system or the vehicle after impact

Working Width

Working Width / Zone of Intrusion

Zone of Intrusion – Real World Consequences

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Placement on Slopes

Slopes can have a significant effect on the performance of barrier:

•In general, barriers mosteffective when placed on 10:1 orflatter slopes

•“Standard” GR was tested on 6:1 and did not contain the vehicle unless it was at least 12’ from the slope break point

12 Feet

Maintain Full Usable Shoulder

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•Discomfort may cause drivers to slow, shift lanes and position

•More of an issue on the right side

•Rule of Thumb: Place as far away from travel lane as practicalwithout affecting function

Shy Line Effect

Barrier Systems

Barrier systems include:

• Standard Sections

• End Treatments

• Transitions

It is important to ensure tension continuity throughout the system!

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Module 8

Flexible Barriers

RDG Chapter 5 & 6

Flexible Systems

•AdvantagesLess severe occupant impactReduced redirectionMore latitude for placement on slopes (cable)Initial Cost

•DisadvantagesConstraints on use for shielding fixed objects(Low tension) cable vulnerable until damaged cable(s) restored

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Generic Cable Barrier

Low-Tension Cable Barrier

Roadside TL‐3 Median TL‐3

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High-Tension Cable Systems

TL‐3 Low Tension 3 StrandI‐26 South Carolina

TL‐4Nucor High TensionI‐10 Louisiana

High Tension vs Low Tension Cable Barrier

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•NCHRP 350 Test Level 3 and 4•3 & 4 Cable Systems

•Variable Post Spacing•Post OptionsDirect DrivenSockets

•Some MASH 2009 Systems available but few MASH 2016 yet

Common Characteristics of High Tension Cable Barrier Systems

Major Differences of High Tension Cable Barrier Systems

•Woven verses Parallel

•Post Stiffness•Cable Connections•Different Cable Heights•Anchor Design

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High Tension Cable Barrier and FDOT IPL

Brifen

http://brifenusa.com/

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Trinity CASS

https://trinityhighway.com/product‐category/barriers/cable‐barriers/

Nucor NU-CABLE

https://nucorhighway.com/cable‐barrier‐products/nu‐cable‐high‐tension/

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Gibraltar

https://gibraltarglobal.com/products/tl‐4‐four‐cable/https://gibraltarglobal.com/products/tl‐4‐four‐cable/

Cable Barrier Terminals

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Cable Barrier Terminals in Weak Soils

Barrier Performance Characteristics

•Design decisions that affect deflection, including placementin a curve

•Placement on slopes

•Dynamic design considerations to address barrierpenetration

•Which side of the median should the cable barrier be placed?

•Narrow median application

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Example Deflection Characteristics

Deflection depends on:• Barrier type• Post spacing• Length betweenanchors

Source NCHRP Report 711

Deflection Characteristics of Cable Barriers

http://www.trb.org/Main/Blurbs/167753.aspx

New York Low Tension Cable System(Video of Mod. MASH 3-11)

Impact angle = 21.6 degreeImpact Speed = 63.1 mph

Cable Heights: 17”, 23”, 29”Post Spacing = 8 ft.

Working Width = 14 ft – 5 inRadius = 440 ft

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Placement on Slopes

• In general, barriers aremost effective whenplaced on 10:1 or flatterslopes

•Cable barriers were testedon 6:1 slopes (in the1980’s) and were found toperform acceptably.

I‐77 South CarolinaWindstar under ride

What about Cable Penetrations?

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Cable placed 4’ offset from 6:1 V‐ditch bottom

Under-Ride Cable Test Video


Vehicle Dynamics Analysis

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Vehicle Dynamics Analysis

Vehicle Travel Direction

Near‐side region

Far‐side region


Successful Test Video

Cable placed 1’ offset from ditch bottom

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Cable Barrier Placement Guidelines for V-Shaped Medians

Source: NCHRP Report 711, http://www.trb.org/Main/Blurbs/167753.aspx

Medians shallowerthan 6H:1V slope

Medians steeper than 6H:1V slope, to avoid

under ride

Medians steeperthan 6H:1V slope, to

avoid over ride

Areas to avoid

Cable Barrier Placement Guidelines for Flat Bottom Medians


Figure 6.3(b) Medians steeper than 6H:1V slope OR flat bottom less than 8 ft wide

Figure 6.3(a) Medians shallower than 6H:1V slope AND flat bottom wider than 8 ft

Areas to avoid

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High Tension Cable Barrier Systems Tested on 4:1 Slopes

40”

30”

20”

10”

Ground

BrifenB‐82B1

NucorB‐193

CASSB‐232

MASH09

GibraltarB‐137C

NCHRP350

GibraltarB‐340

MASH16

MASH 2016 Tests for Cable Median Barrier

The most significant changes in the 2nd edition of MASH is for testing of cable barrier

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Which Side of the Median Should Cable Barrier be Placed?

http://onlinemanuals.txdot.gov/txdotmanuals/rdw/median_barrier.htm

US 26, Mt. Hood, OR

US 189, Provo Canyon, UT

Cable Barrier in Narrow Medians: Case Study in Risk Management

PA 56, Johnstown, PA

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Semi Rigid Barriers

Module 9

How Guardrail Reacts When Hit

•Beam guardrail is designed todeflect when hit

•Blockouts reduce potential forsnagging on the post

•The posts rotate in the soilFor older strong post w‐beam, thebolt should pull through the rail

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27”

28”

27 5/8”

31”?Source: FHWA Letter B‐64

(2/14/2000)

Source: Task Force 13 Guide to Standardized Roadside Hardware

What is the “Standard” Height of W-Beam Guardrail?

SPWB MASH Test: Steel Post, Wood Blockout, 27 5/8” Height

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SPWB MASH Test: Wood Post, Wood Blockout, 27 5/8” Height

FHWA Letter B‐212 (Steel Post) & B‐230A (SYP post)

Midwest Guardrail System (MGS)

MGS uses:

•Same w‐beam rail

•Same 6’ posts

•Top rail height = 31”•12” deep blockout•Midspan rail splices (between posts)

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Working Width – 48.6”FHWA Letter B‐212

MGS Test: Steel Post, 12” Wood Blockout, 31” Height

Working Width – 53.8”FHWA Letter B‐230A

MGS Test: Wood Post, 12” Wood Blockout, 31” Height

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Eligibility Letter B‐ 240

MGS Test: Steel Post, 8” Wood Blockout, 31” Height

Working Width – 44.3”

MGS TL-2 Test: Steel Posts at 12’-6” Spacing, Blockouts, 31” Height

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W-Beam in Median

•27” SPWB guardrail failed MASH TL‐3

•31” MGS guardrail passed8” blockout tested12” blockout acceptable

Placement of Barriers

•Deflection distance / Working width

•Placement on slopes

•Barrier and curbs•Soil support

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Dynamic Deflection – the maximum lateral displacement of the test article on the traffic side that occurs during the impact.

Zone of Intrusion (ZOI) – the region measured above and behind the face of a barrier system where an impacting vehicle or any major part of the system may extend during an impact

Working Width – the distance between the barrier face before impact and the maximum lateral position of any major part of the system or the vehicle after impact.

DynamicDeflection

Working Width

Dynamic Deflection, Zone of Intrusion, & Working Width

Insufficient Deflection Distance

•Eliminate or relocate the obstacle

•Relocate rail•Modify the barrier for reducedworking width

•Use a stiffer barrierMay need a transition

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Reducing W-beam Working Width

•Reduce post spacing to 3’‐1 ½”(SPWB but notMGS)

•Reduce post spacing again to 1’‐6 ¾”(SPWB and MGS)

•Double‐up (nest) rail element

•Use a crash tested transition to rigidbarrier

https://www.roadsidepooledfund.org/testing‐of‐midwest‐guardrail‐systems‐with‐reduced‐post‐spacing‐for‐mash‐compliance‐610211‐01/

FDOT Standard Plans 536‐001

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Placement of Beam Barrier on 6H:1V Slopes

Placing strong‐post w‐beam farther out on a 6H:1V slope was acceptable in the past, now the slopes should be 10H:1V unless otherwise tested.

MGS Test on 8V:1H Slopes

•The MGS system wassuccessfully tested toNCHRP 350 TL‐3 on8H:1V slopes

•Tested with MGS 5’ frombreak point (worst case)

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Barrier and Curbs

6” Curb 6” in Front of MGS, TL-3 Test

Pass

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6” Curb 8’ in Front of MGS, TL-3 Test

Fail

6” Curb 6’ in Front of MGS, TL-2 Test

Pass

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Alternative Curb Options

Soil Support

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2’ from back of post is recommended with 6’ posts

• A design with 6’ posts at theslope break passed MASHtesting but with greaterdeflection

• A design with 8’ long postsplaced beyond the slope breakpassed MASH testing

Soil Support

2 feetMeasured From

Back of Post

Hinge Point

FHWA

Soil Support Considerations

2’ Minimum Clearance near Slope Break Locations

1. 2’ offset from hinge point usually sufficient for 6’ posts and strong soil

2. Increasing the post length by 1’ or more allows for offset of up to 1 ft

3. Increasing post length and reducing post spacing allows for <1 ft

2 feet

Measured From

Back of PostHinge Point

Post Length?

RDG Section 5.6.1

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MGS TL-3 Test with Posts @ Slopebreak of 2H:1V Slope

Posts•6’ long steel post tested•6’‐3” spacingBlocks•12” block tested•8” and no block consideredacceptable

•Not recommended for weaksoils

Working Width – 77.4”

MGS TL-3 Test with Steel Posts on a 2H:1V Slope

•Posts•8’ long W6x9 posts tested•6’‐3” post spacing•Not recommended with Woodposts at this time

•Blocks•8” block tested•12” block acceptable•Not recommended withoutblockouts at this time

Working Width – 55.2”FHWA Letter B‐261

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Guardrail on Gabion Walls

MGS with No Blockouts on Wire-faced, Rock Gabion Wall

Working Width – 45.2”FHWA Letter B‐243A

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Intercepted Length of Need

FHWA Letter B‐209 – NCHRP 350 TL 2

FDOT Standard Plans 536‐001CRT Systems for Side Roads & Driveways

MASH TL-3 Test of Short Radius Guardrail

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MASH TL-2 Test Short Radius Guardrail

Preliminary Design from NCHRP 15-53

Key Characteristics:•W‐beam barrier (31” height) steel postswith 8” wood blockouts

•10‐gauge thickness for all rails•24 ft tangent section on primary road•35 ft tangent section on secondary road•3/4” diameter cable placed at 12‐in fromground (about 5 in from rails)

•Another cable placed along the center ofthe w‐beam

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Clear Area Needed Behind Rail

Interfering Drainage Devices

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MGS - Omitting 1 post

•No post modifications

•Can be used with wood or steel posts, but NOT with curbs•Can be used with 8” and 12” blockouts, but NOT with thenon‐blocked system

•Working Width 50.1”

•Limit 1 per 50’

12’-6”

MGS TL-3 VideosOmitting 1 post

Working Width 50.1” Limit 1 per 50’

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For 27 ¾” Guardrail•3 weakened posts on each side ofspan with double 8” blockouts

•100 feet of nested rail

For 31” (MGS) Guardrail•3 weakened posts on each side ofspan with single 12” blockouts

•Single rail

FHWA Letter B‐ 58 (350) & B‐189 (MASH)

Long Span Designs

MGS TL-3 Test Omitting 3 Posts

Working Width – 94” Eligibility Letter B‐189

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RDG Figure 5‐52FHWA Letter B‐64B

Paving Around Posts

FDOT Standard Plan 536‐001

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Posts in Rock

A<18” A ≥18”

RDG Figure 5‐51FHWA Letter B‐64B

Posts in Rock

FDOT Standard Plans 536‐001Shallow Mount

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Rigid & Concrete Barriers

RDG Chapter 5 & 6

Module 10

MASH Test Levels

TESTLEVEL

VEHICLEIMPACTSPEED

IMPACT ANGLE

TL-1 Car, PU 31 mph 25°



TL-4 TL3 + 22,000# SU 56 mph 15°

TL-5 TL3 + 80,000# Semi 50 mph 15°

TL-6 TL3 + 80,000# Tanker 50 mph 15°

TL‐4(18000 lb – 350)

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Single Slope Barrier Video

• CalTrans design – 9.1 degree slope

• TxDot design – 10.8 degree slope

TxDOT T224MASH TL‐542” height

Openings were provided for aesthetics

TxDOT T222MASH TL‐332 ¾” height

Precast concrete anchored to deck

Vertical Wall Barrier Video

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Barriers for Large Trucks

•TL‐3 – Passenger Vehicles (Car and PU) 32” based on NJ shape testing

•TL‐4 – Single Unit Truck (22,000#) 36” based on Single Slope testing

•TL‐5 Tractor Trailer (80,000#) 42” based on Vertical Wall testing

Note – No national criteria for when to use TL‐4, 5, or 6

• Only one TL‐6 barrier has been tested and there are alimited number of these around the country

• Height – 90”

TL-6 Texas Tall Wall Video

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FHWA Letter B‐182

Considerations for Taller Barriers

• Sight Distance

• Head Slap

Portable Traffic Barriers

•Concrete Safety Shape•Moveable Systems

•Low‐Profile Concrete Barrier

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Portable Concrete Barriers Details

•Shape•Connections•Deflection•Anchorage

RDG Chapter 9

FHWA Letter B‐215

Iowa F-Shape Precast Barrier Video

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Deflection Factors

•Number of joints

•Connection type•Anchorage

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Anchoring PCB to Bridge Deck

•NCHRP 350 test•On edge of deck (no lateral offset)•1‐½” dia, 21‐¼” long pin•No significant damage to deck•Max dynamic deflection = 11.5”

FHWA Letter B‐206

Anchoring PCB to Asphalt

•MASH Test•12” in front of slope break•1‐½” dia, 48” long pin•Max Dynamic deflection = 17.8”

FHWA Letter Pending

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Anchoring PCB Video

•Guidebook for Use of Pinned‐Down Temporary ConcreteBarriers in Limited Space Applications

https://www.roadsidepooledfund.org/wp‐content/uploads/2017/06/ ReportNo605071_Guidebook_Pinned_Barrier.rev2_.pdf

FDOT Standard Plans 102-110

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QuickChange Moveable Barrier System

FHWA Letter B‐277

Low Profile Barrier

https://www.roadsidepooledfund.org/longitudinal‐barrier/mash‐tl‐3‐low‐profile‐concrete‐barrier/

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FDOT Low Profile Barrier

FDOT Standard Plans 102‐120

www.SeminolePrecast.com

Selecting Higher Test Level Barriers

•Adverse Geometrics

•Increased Percentage of Trucks•Severe Consequences of Penetration•Crash History

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Questions/Comments

Day 3 To-Dos

• MASH Crash Testing Overview Video(15 minutes)https://connectdot.connectsolutions.com/rsd_mash/

• Visit https://www.roadsidepooledfund.org/mash‐implementation/search/

Documents

Combating Roadway Departures Roadside Safety Design