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Median Barriers Chapter 6 AASHTO Roadside Design Guide

Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)

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Page 1: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)

Median Barriers

Chapter 6AASHTO Roadside Design Guide

Page 2: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)

OVERVIEW

• Warrants• Median Barrier Selection• Median Barrier Location (placement within

median)

Page 3: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)

Figure 6.180

70

60 Barrier Barrier Not

50 Evaluate Need For Barrier Optional Normally

40 Considered

30

20

10

00 2 4 6 8 10 12 14 16 18 20

Median Width (Meters)

*Ave

rage

Daily T

raff

ic(T

hous

ands

)

Figure 6.1

*Based on a 5-Year Projection

Page 4: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)

Warrants

• FHWA memorandum to field offices• NCHRP Median Barrier Warrant Study• AASHTO Technical Committee for

Roadside Safety (Roadside Design Guide)

Page 5: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)

Initial Survey Findings…

• Requests must be specific!• FARS data not reliable source for cross-

over crashes• Many state DOTs unable to identify true

cross-over crashes or to correlate crashlocations with median width/characteristics

• Revising warrants upwards likely to reducecross median crashes in several states

Page 6: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)

MEDIAN BARRIER WARRANT (AASHTO 2002 Figure 6.1)

1999-2002 NJ Median Cross Over Crashes

0

10000

20000

30000

40000

50000

60000

70000

80000

90000

100000

110000

120000

0 10 20 30 40 50 60 70 80 90 100 110 120

Median Width (Feet)

(AA

DT

)

Barrier Not Normally Considered

Barrier Optional

Evaluate Need for Barrier

Page 7: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)

NC Cross-median Crashes

0

20000

40000

60000

80000

100000

120000

140000

0 50 100 150 200 250

Median Width (feet)

Ave

rag

e D

aily

Tra

ffic

(veh

/day

)

Evaluate Need forBarrier

Barrier Optional

Barrier Not Normally Considered

Page 8: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)

Research Objectives forNCHRP Project 17-14(2)

• Survey State Transportation Agencies regardingmedian practices.

• Analyze cross-median crash data from NC.• Analyze median-involved crash data from CA,

NC, and OH.• Conduct before-after analysis of slope

flattening projects in IA.• Recommend revised median barrier warrant

criteria and other median design guidelines.

Page 9: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)
Page 10: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)
Page 11: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)

Other STA Median Barrier Practices

• Washington DOT– Recommend barrier on full-access controlled

highways with posted speed > 45-mph andmedian < 50-ft wide.

• Florida DOT– Install barrier on all divided highway

medians < 64-ft.• North Carolina DOT

– Install barrier on all divided freeway medians< 70-ft.

Page 12: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)

Recommended Median Barrier Warrant

Median Width (feet)

Ave

rage

Dai

ly T

raff

ic (t

hous

ands

)

0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

70

80

90

100

Median Barrier Optional

Study ofCrash HistoryRecommended

Median BarrierWarranted

Page 13: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)

Current Status

Page 14: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)

Figure 6.180

70

60 Barrier Barrier Not

50 Evaluate Need For Barrier Optional Normally

40 Considered

30

20

10

00 2 4 6 8 10 12 14 16 18 20

Median Width (Meters)

*Ave

rage

Daily T

raff

ic(T

hous

ands

)

Figure 6.1

*Based on a 5-Year Projection

BarrierNOTwarrantedunless cost-effective

BarrierwarrantedunlessNOT cost-effective

Barrier warranted

Page 15: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)

Median Barrier Systems

• 3-Strand Cable (generic & high tension)• W-Beam (weak post)• Box-Beam• W-Beam (strong post) w/rubrail• Thrie Beam• Modified Thrie Beam• Concrete Safety Shapes

Page 16: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)
Page 17: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)

3 strand cable system

Page 18: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)
Page 19: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)
Page 20: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)
Page 21: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)
Page 22: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)
Page 23: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)
Page 24: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)
Page 25: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)

Thrie beam

Page 26: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)
Page 27: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)

NJ Concrete Barrier

Page 28: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)
Page 29: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)

42 inch safety shape

Page 30: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)

Constant slope barriers

Page 31: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)
Page 32: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)

Median Barrier Location

Page 33: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)

Barriers

Barrier

Barrier

11

1

1

11010

10

6

1

S2S3

Edge ofTraveledWay

Edge ofTraveledWay

WW/2 W/2

a b c d e

Illustration 1

Illustration 2

Illustration 3

Figure 6.11

Page 34: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)
Page 35: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)
Page 36: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)
Page 37: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)
Page 38: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)
Page 39: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)
Page 40: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)
Page 41: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)
Page 42: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)
Page 43: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)
Page 44: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)
Page 45: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)

What we know….

• Many cross-median crashes occur on mediansover 30 feet wide

• Median encroachments are likely to increase withhigher traffic volumes

• Cross-over crashes are severe• Median barriers can significantly reduce cross

over crashes• Barrier selection and placement are critical for

optimal performance

Page 46: Median Barriers - Transportation.orgaii.transportation.org/Documents/FHWA-AASHTORSDGChapter6.pdf · Chapter 6 AASHTO Roadside Design Guide. ... Roadside Safety (Roadside Design Guide)

What we don’t know

• What median width/ADT combinationsresult in cost-effective warrants?

• How should crash history be considered?• How will cable, metal-beam or concrete

median barriers perform when struck by avehicle coming UP a slope into the barrier?

• When will new warrants be adopted byAASHTO?