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Detours – Selection and DesignDetours – Selection and Design
Highways & Engineering ConferenceMarch 2, 2006
Presenters:Presenters:
Paul Ferry, Highways Engineer Lesly Tribelhorn, Highways Design Engineer
ObjectivesObjectives
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 DetoursTypes of Detours
Types of DetoursTypes of Detours
Detour traffic onto an existing route Temporary detour Median crossovers (divided highways) Lane closures Part-width construction
Interstate/FreewayInterstate/Freeway
Interstate/FreewayInterstate/Freeway Median crossovers – design considerations
GuardrailBridge widthsInterchange proximity and accessReview distance between crossoversLocation (topography, geometrics, distance between)DrainageFuture projects
Interstate/FreewayInterstate/Freeway
Median crossovers – safety+ Ingress/egress controlled+ Interstate standards met– Two-way traffic– Cross over of traffic– No passing
Interstate/FreewayInterstate/Freeway Median crossovers – cost considerations
Construct & remove crossoverTraffic control (length, maintenance)Guardrail revisions
Median crossovers – site constraintsTopography considerations for crossover locationNo environmentalNo R/W
Interstate/FreewayInterstate/Freeway
Lane closure – design considerationsBridge widthsTemporary barrier rail– Length of area to be protected– Barrier deflection– Taper rates– End treatment
Interstate/FreewayInterstate/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/FreewayInterstate/Freeway
Lane closure – cost considerationsTraffic control
Lane closure – site constraintsInterchange locations
Interstate/FreewayInterstate/Freeway
Temporary detours – design considerationsUsually for culvert replacement in high fillMay need temporary widening, barrier railJack and bore instead (≤48” diameter)?Need temporary access control fence?Proximity of interchanges
Interstate/FreewayInterstate/Freeway
Temporary detours – safety+ Short length– Driver expectations violated
Temporary detours – cost considerationsConstruction & removal of detourTraffic control minimized
Interstate/FreewayInterstate/Freeway
Temporary detours – site constraintsEnvironmental involvement possibleR/W, access fence possible
Interstate/FreewayInterstate/Freeway
Detour traffic onto an existing routeBridge widths, structural capacity, clearanceRoad surfacing and structureRoadway widthSafety issues (mixing traffic, accesses, standards)Clear zoneLength and duration of detourCosts - traffic control and surfacing improvement
Interstate/FreewayInterstate/Freeway
Two-lane rural routesTwo-lane rural routes
Two-lane rural routesTwo-lane rural routes
Detour onto an existing route - designCost of temporary detour excessive?Bridge widths and capacityAdequate clearanceRoadway widths and structural capacityClear zoneWork with construction and maintenance
Two-lane rural routesTwo-lane rural routes
Detour onto an existing routeSafety depends on route selectedCosts minimal – traffic control, route maintenanceSite constraints should be minimal
Two-lane rural routesTwo-lane rural routes
Temporary detours
Two-lane rural routesTwo-lane rural routes
Temporary detours Replacement of drainage structuresExcavation leaves insufficient room for traffic
Design Criteria – temporary detoursDesign Criteria – temporary detours
AlignmentAlignment
Design speedRoute design speed – 10 mphLocationDurationSight distance
AlignmentAlignment
LocationTopography – which side most economicalUtility impactsR/W issuesEnvironmental impactsImpacts to adjacent developmentsAccesses
AlignmentAlignment
Request adequate survey for proper design Offset and detour length Normal crown horizontal curves Adequate cover over culverts Bridge freeboard Downstream location preferred
SurfacingSurfacing
Traffic loading Detour duration
Duration of Detour Operation Current
ADT
< 5 Days 5 - 30 Days 31 Days – 3 Months
> 3 Months
< 500 gravel gravel dust palliative dust palliative
500 - 1499 gravel dust palliative dust palliative PMS
1500 - 6000 dust palliative dust palliative PMS PMS
> 6000 dust palliative PMS PMS PMS
GUIDELINES FOR SELECTION OF DETOUR SURFACING
Figure 15.3G
Roadway WidthRoadway Width
24’ adequate for most ADT < 400, consider narrower lanes
10’ – 11’Two-way, one lane
Grading/side slopesGrading/side slopes
Typically 3:1Traffic volumesDetour durationTemporary barrierGeotech involvement!Detour embankment part of roadway?
DrainageDrainage
Size provided by Hydraulics Address sequencing for flowing streams
Safety and costsSafety and costs
Safety level variesDesignTrafficDriver expectations
Costs can be significantConstruction and removalR/W, utility movesTraffic control and maintenance
Environmental considerationsEnvironmental considerations
Environmental considerationsEnvironmental considerations
Coordinate with district biologist Special construction methods for streams Wetland, historic, archaeological site avoidance
Part-width constructionPart-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 constructionPart-width construction
Safety can be compromisedDriver expectation – sudden speed reduction?Design may be necessaryOffset by short construction time
Cost savings can be significant Evaluate environmental, R/W involvement
Lane closuresLane closures
Special case for two-lane highwayCosts or construction issues for other detour typesSafety compromised - very short duration only24-hour flaggers for safetyShort length preferred (sight distance, safety)Costs low – traffic control onlyEnvironmental, other impacts minimal
Two-lane rural routesTwo-lane rural routes
Other options?Other options?
Other options?Other options?
Offset alignment and use PTWDetours for drainage installation not neededMore efficient construction operationEnhanced safety
Jack and bore Road closures
Urban constructionUrban construction
Urban constructionUrban construction
Pedestrian/ADA access Utility considerations Emergency vehicle access Impacts to businesses Public relations Worker safety
Urban constructionUrban construction
Costs and safety comparisons Depend on work, location Specific to project
Urban constructionUrban construction
Detour traffic onto an existing routeClose one block at a timeSequencing and coordination
Urban constructionUrban construction
Existing route detour considerations:Additional traffic loads on adjacent streetsSurfacing improvements necessary?Pedestrian/ADA accommodationBusiness access – signing criticalHospital, residences, school access
Urban constructionUrban construction
Lane closuresRoom to accommodate traffic and construction workNeed positive separation for utility work in trenches?Access to businesses - may need detourPedestrian/ADA access on both sides of street
Urban constructionUrban construction
Temporary detour & median crossoversUsually impracticalCostsAdequate room
Safety features compromiseSafety features compromise
Detour traffic onto an existing route Temporary detour Median crossovers (divided highways) Lane closures Part-width construction
General questions to addressGeneral questions to address
General questions to addressGeneral 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 projectWide loads
SummarySummary
Types of detours Types of highway Considerations:
Design issuesCost comparisonsSafety compromisesEnvironmental impacts; other site constraints
ResourcesResources
MDT Road Design Manual; 2006Chapter 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