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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

Detours – Selection and Design

Highways & Engineering Conference

March 2, 2006

presenters
Presenters:
  • Paul Ferry, Highways Engineer
  • Lesly Tribelhorn, Highways Design Engineer
objectives
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
types of detours7
Types of Detours
  • Detour traffic onto an existing route
  • Temporary detour
  • Median crossovers (divided highways)
  • Lane closures
  • Part-width construction
interstate freeway9
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
interstate freeway10
Interstate/Freeway
  • Median crossovers – safety
    • Ingress/egress controlled
    • Interstate standards met
    • Two-way traffic
    • Cross over of traffic
    • No passing
interstate freeway11
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
interstate freeway40
Interstate/Freeway
  • Lane closure – design considerations
    • Bridge widths
    • Temporary barrier rail
      • Length of area to be protected
      • Barrier deflection
      • Taper rates
      • End treatment
interstate freeway41
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
interstate freeway42
Interstate/Freeway
  • Lane closure – cost considerations
    • Traffic control
  • Lane closure – site constraints
    • Interchange locations
interstate freeway43
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
interstate freeway44
Interstate/Freeway
  • Temporary detours – safety
    • Short length
    • Driver expectations violated
  • Temporary detours – cost considerations
    • Construction & removal of detour
    • Traffic control minimized
interstate freeway45
Interstate/Freeway
  • Temporary detours – site constraints
    • Environmental involvement possible
    • R/W, access fence possible
interstate freeway46
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
two lane rural routes49
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
two lane rural routes50
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
two lane rural routes51
Two-lane rural routes
  • Temporary detours
two lane rural routes53
Two-lane rural routes
  • Temporary detours
    • Replacement of drainage structures
    • Excavation leaves insufficient room for traffic
alignment
Alignment
  • Design speed
    • Route design speed – 10 mph
    • Location
    • Duration
    • Sight distance
alignment57
Alignment
  • Location
    • Topography – which side most economical
    • Utility impacts
    • R/W issues
    • Environmental impacts
    • Impacts to adjacent developments
    • Accesses
alignment58
Alignment
  • Request adequate survey for proper design
  • Offset and detour length
  • Normal crown horizontal curves
  • Adequate cover over culverts
  • Bridge freeboard
  • Downstream location preferred
surfacing
Surfacing
  • Traffic loading
  • Detour duration
roadway width
Roadway Width
  • 24’ adequate for most
  • ADT < 400, consider narrower lanes
    • 10’ – 11’
    • Two-way, one lane
grading side slopes
Grading/side slopes
  • Typically 3:1
    • Traffic volumes
    • Detour duration
    • Temporary barrier
    • Geotech involvement!
    • Detour embankment part of roadway?
drainage
Drainage
  • Size provided by Hydraulics
  • Address sequencing for flowing streams
safety and costs
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
environmental considerations67
Environmental considerations
  • Coordinate with district biologist
  • Special construction methods for streams
  • Wetland, historic, archaeological site avoidance
part width construction
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?
part width construction69
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
lane closures
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
other options74
Other options?
  • Offset alignment and use PTW
    • Detours for drainage installation not needed
    • More efficient construction operation
    • Enhanced safety
  • Jack and bore
  • Road closures
urban construction76
Urban construction
  • Pedestrian/ADA access
  • Utility considerations
  • Emergency vehicle access
  • Impacts to businesses
  • Public relations
  • Worker safety
urban construction77
Urban construction
  • Costs and safety comparisons
  • Depend on work, location
  • Specific to project
urban construction78
Urban construction
  • Detour traffic onto an existing route
    • Close one block at a time
    • Sequencing and coordination
urban construction79
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
urban construction80
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
urban construction81
Urban construction
  • Temporary detour & median crossovers
    • Usually impractical
    • Costs
    • Adequate room
safety features compromise
Safety features compromise
  • Detour traffic onto an existing route
  • Temporary detour
  • Median crossovers (divided highways)
  • Lane closures
  • Part-width construction
general questions to address84
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
summary
Summary
  • Types of detours
  • Types of highway
  • Considerations:
    • Design issues
    • Cost comparisons
    • Safety compromises
    • Environmental impacts; other site constraints
resources
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
resources87
Resources
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