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

ResourcesResources

Paul Ferry(406) 444-6244pferry@mt.gov

Lesly Tribelhorn(406) 444-6242ltribelhorn@mt.gov