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  Think about environmental, other site constraints  Know where to look for information

Types of Detours

 Detour traffic onto an existing route  Temporary detour  Median crossovers (divided highways)  Lane closures  Part-width construction

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/Freeway  Median crossovers – safety + Ingress/egress controlled + Interstate standards met – Two-way traffic – Cross over of traffic – No passing

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/Freeway  Lane closure – design considerations Bridge widths Temporary barrier rail –Length of area to be protected –Barrier deflection –Taper rates –End treatment

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/Freeway  Lane closure – cost considerations Traffic control  Lane closure – site constraints Interchange locations

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/Freeway  Temporary detours – safety + Short length – Driver expectations violated  Temporary detours – cost considerations Construction & removal of detour Traffic control minimized

Interstate/Freeway  Temporary detours – site constraints Environmental involvement possible R/W, access fence possible

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

Interstate/Freeway

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 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 routes  Temporary detours

Two-lane rural routes  Temporary detours Replacement of drainage structures Excavation leaves insufficient room for traffic

Design Criteria – temporary detours

Alignment  Design speed Route design speed – 10 mph Location Duration Sight distance

Alignment  Location Topography – which side most economical Utility impacts R/W issues Environmental impacts Impacts to adjacent developments Accesses

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  Traffic loading  Detour duration

Roadway Width  24’ adequate for most  ADT < 400, consider narrower lanes 10’ – 11’ Two-way, one lane

Grading/side slopes  Typically 3:1 Traffic volumes Detour duration Temporary barrier Geotech involvement! Detour embankment part of roadway?

Drainage  Size provided by Hydraulics  Address sequencing for flowing streams

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 considerations

 Coordinate with district biologist  Special construction methods for streams  Wetland, historic, archaeological site avoidance

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 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  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

Two-lane rural routes

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 construction

 Pedestrian/ADA access  Utility considerations  Emergency vehicle access  Impacts to businesses  Public relations  Worker safety

Urban construction  Costs and safety comparisons  Depend on work, location  Specific to project

Urban construction  Detour traffic onto an existing route Close one block at a time Sequencing and coordination

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 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 construction  Temporary detour & median crossovers Usually impractical Costs Adequate room

Safety features compromise  Detour traffic onto an existing route  Temporary detour  Median crossovers (divided highways)  Lane closures  Part-width construction

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  Types of detours  Types of highway  Considerations: Design issues Cost comparisons Safety compromises Environmental impacts; other site constraints

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

Resources  Paul Ferry (406)  Lesly Tribelhorn (406)