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Detours – Selection and Design. Highways & Engineering Conference March 2, 2006. Presenters:. Paul Ferry, Highways Engineer Lesly Tribelhorn, Highways Design Engineer. Objectives. Know which types of detours are appropriate Apply proper design criteria Consider safety and costs

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Detours – Selection and Design

Highways & Engineering Conference

March 2, 2006


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Presenters:

  • Paul Ferry, Highways Engineer

  • Lesly Tribelhorn, Highways Design Engineer


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Objectives

  • Know which types of detours are appropriate

  • Apply proper design criteria

  • Consider safety and costs

  • Think about environmental, other site constraints

  • Know where to look for information



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Types of Detours

  • Detour traffic onto an existing route

  • Temporary detour

  • Median crossovers (divided highways)

  • Lane closures

  • Part-width construction



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Interstate/Freeway

  • Median crossovers – design considerations

    • Guardrail

    • Bridge widths

    • Interchange proximity and access

    • Review distance between crossovers

    • Location (topography, geometrics, distance between)

    • Drainage

    • Future projects


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Interstate/Freeway

  • Median crossovers – safety

    • Ingress/egress controlled

    • Interstate standards met

    • Two-way traffic

    • Cross over of traffic

    • No passing


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Interstate/Freeway

  • Median crossovers – cost considerations

    • Construct & remove crossover

    • Traffic control (length, maintenance)

    • Guardrail revisions

  • Median crossovers – site constraints

    • Topography considerations for crossover location

    • No environmental

    • No R/W


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Interstate/Freeway

  • Lane closure – design considerations

    • Bridge widths

    • Temporary barrier rail

      • Length of area to be protected

      • Barrier deflection

      • Taper rates

      • End treatment


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Interstate/Freeway

  • Lane closure – safety

    • Directional traffic separated

    • Interstate standards met

    • Access controlled

    • Excavation located next to travel lane

    • Bridge work – extended duration

    • No passing


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Interstate/Freeway

  • Lane closure – cost considerations

    • Traffic control

  • Lane closure – site constraints

    • Interchange locations


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Interstate/Freeway

  • Temporary detours – design considerations

    • Usually for culvert replacement in high fill

    • May need temporary widening, barrier rail

    • Jack and bore instead (≤48” diameter)?

    • Need temporary access control fence?

    • Proximity of interchanges


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Interstate/Freeway

  • Temporary detours – safety

    • Short length

    • Driver expectations violated

  • Temporary detours – cost considerations

    • Construction & removal of detour

    • Traffic control minimized


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Interstate/Freeway

  • Temporary detours – site constraints

    • Environmental involvement possible

    • R/W, access fence possible


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Interstate/Freeway

  • Detour traffic onto an existing route

    • Bridge widths, structural capacity, clearance

    • Road surfacing and structure

    • Roadway width

    • Safety issues (mixing traffic, accesses, standards)

    • Clear zone

    • Length and duration of detour

    • Costs - traffic control and surfacing improvement




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Two-lane rural routes

  • Detour onto an existing route - design

    • Cost of temporary detour excessive?

    • Bridge widths and capacity

    • Adequate clearance

    • Roadway widths and structural capacity

    • Clear zone

    • Work with construction and maintenance


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Two-lane rural routes

  • Detour onto an existing route

    • Safety depends on route selected

    • Costs minimal – traffic control, route maintenance

    • Site constraints should be minimal


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Two-lane rural routes

  • Temporary detours


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Two-lane rural routes

  • Temporary detours

    • Replacement of drainage structures

    • Excavation leaves insufficient room for traffic


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Design Criteria – temporary detours


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Alignment

  • Design speed

    • Route design speed – 10 mph

    • Location

    • Duration

    • Sight distance


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Alignment

  • Location

    • Topography – which side most economical

    • Utility impacts

    • R/W issues

    • Environmental impacts

    • Impacts to adjacent developments

    • Accesses


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Alignment

  • Request adequate survey for proper design

  • Offset and detour length

  • Normal crown horizontal curves

  • Adequate cover over culverts

  • Bridge freeboard

  • Downstream location preferred


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Surfacing

  • Traffic loading

  • Detour duration


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Roadway Width

  • 24’ adequate for most

  • ADT < 400, consider narrower lanes

    • 10’ – 11’

    • Two-way, one lane


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Grading/side slopes

  • Typically 3:1

    • Traffic volumes

    • Detour duration

    • Temporary barrier

    • Geotech involvement!

    • Detour embankment part of roadway?


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Drainage

  • Size provided by Hydraulics

  • Address sequencing for flowing streams


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Safety and costs

  • Safety level varies

    • Design

    • Traffic

    • Driver expectations

  • Costs can be significant

    • Construction and removal

    • R/W, utility moves

    • Traffic control and maintenance



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Environmental considerations

  • Coordinate with district biologist

  • Special construction methods for streams

  • Wetland, historic, archaeological site avoidance


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Part-width construction

  • Design considerations:

    • Low speed environment?

    • Wide enough for oversize loads?

    • Bridges impacted?

    • Practical locations available for temp. detour?

    • Can temporary barrier rail reduce widening?


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Part-width construction

  • Safety can be compromised

    • Driver expectation – sudden speed reduction?

    • Design may be necessary

    • Offset by short construction time

  • Cost savings can be significant

  • Evaluate environmental, R/W involvement


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Lane closures

  • Special case for two-lane highway

    • Costs or construction issues for other detour types

    • Safety compromised - very short duration only

    • 24-hour flaggers for safety

    • Short length preferred (sight distance, safety)

    • Costs low – traffic control only

    • Environmental, other impacts minimal




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Other options?

  • Offset alignment and use PTW

    • Detours for drainage installation not needed

    • More efficient construction operation

    • Enhanced safety

  • Jack and bore

  • Road closures



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Urban construction

  • Pedestrian/ADA access

  • Utility considerations

  • Emergency vehicle access

  • Impacts to businesses

  • Public relations

  • Worker safety


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Urban construction

  • Costs and safety comparisons

  • Depend on work, location

  • Specific to project


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Urban construction

  • Detour traffic onto an existing route

    • Close one block at a time

    • Sequencing and coordination


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Urban construction

  • Existing route detour considerations:

    • Additional traffic loads on adjacent streets

    • Surfacing improvements necessary?

    • Pedestrian/ADA accommodation

    • Business access – signing critical

    • Hospital, residences, school access


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Urban construction

  • Lane closures

    • Room to accommodate traffic and construction work

    • Need positive separation for utility work in trenches?

    • Access to businesses - may need detour

    • Pedestrian/ADA access on both sides of street


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Urban construction

  • Temporary detour & median crossovers

    • Usually impractical

    • Costs

    • Adequate room


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Safety features compromise

  • Detour traffic onto an existing route

  • Temporary detour

  • Median crossovers (divided highways)

  • Lane closures

  • Part-width construction



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General questions to address

  • ADT and truck traffic; emergency vehicle use

  • Site considerations

  • Can the road be closed to through traffic?

  • Are there adjacent projects?

  • Are there other projects that may be affected?

    • Detour onto another construction project

    • Wide loads


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Summary

  • Types of detours

  • Types of highway

  • Considerations:

    • Design issues

    • Cost comparisons

    • Safety compromises

    • Environmental impacts; other site constraints


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Resources

  • MDT Road Design Manual; 2006

    • Chapter 15

  • AASHTO: A Policy on Geometric Design of Highways and Streets (Green Book); 2004

  • AASHTO: Guidelines for Geometric Design of Very Low-Volume Local Roads (ADT < 400); 2001


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Resources


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