Detours – Selection and Design

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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
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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
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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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Interstate/Freeway
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Two-lane rural routes
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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 lt 400, consider narrower lanes
• 10 11
• Two-way, one lane

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Grading/side slopes

• Typically 31
• 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
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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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Two-lane rural routes
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Other options?
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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
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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
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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 lt 400) 2001

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Resources

• Paul Ferry
• [phone]
• pferry_at_mt.gov
• Lesly Tribelhorn
• [phone]
• ltribelhorn_at_mt.gov