Presentation on theme: "Kittelson & Associates, Inc. University of Utah January 2014"— Presentation transcript:
1 Kittelson & Associates, Inc. University of Utah January 2014 NCHRP 15-34A Performance-Based Analysis of Geometric Design of Highways and StreetsKittelson & Associates, Inc.University of UtahJanuary 2014
2 Presentation Outline Project Background and Overview Information GatheringProject Work PlanNCHRP Report
3 Presentation Outline Project Background and Overview Information GatheringProject Work PlanNCHRP Report
4 Project Background and Overview Past NCHRP 15-34Transition to NCHRP 15-34AProject TeamProject Goals
5 Project Background – NCHRP 15-34 Past NCHRP 15-34The original intent of NCHRP project was to facilitate the transference of research findings and performance-prediction technologies to application within highway and street decision-making processes.Transition to NCHRP 15-34AJanuary 2007 Interim Report 1February 2007 Project Panel MeetingFall 2007 Principal Investigator Change2008/2009 Conduct WorkJune 2009 Project Panel MeetingMarch 2010 Project StoppedLate Summer 2012 Project NCHRP 15-34A Initiated
6 Project Overview – NCHRP 15-34A Project TeamKittelson & Associates, Inc. – Brian Ray and Erin FergusonUniversity of Utah – RJ PorterDr. John MasonProject GoalsReview past material developed under NCHRP 15-34Develop NCHRP Report 15-34ASummarize research finding in the Supplemental Research Materials ReportArchived material, additional research details, AASHTO Green Book revisions, and future suggested research
7 Presentation Outline Project Background and Overview Information GatheringProject Work PlanNCHRP Report
8 Information Gathering Key Materials Obtained from NCHRP 15-34Original proposalOriginal work planPhase I working filesFirst Interim ReportFramework ConstructionUpdate on project activitiesDraft of Second Interim ReportKwon Final ThesisPresentation files from TRB workshopsPanel comments to proposal and both interim reportsPanel Meeting notes from two panel meetings
9 Information Gathering Material to be archivedInformation primarily from NCHRP First Interim Report (January 2007)definitions and timing of design decisionsrecommended performance measurescapabilities of performance prediction toolssensitivity of performance measures to geometric design decisionsNCHRP archived material is located:https://sites.google.com/site/nchrp1534archive/
10 Information Gathering Material used NCHRP Report 15-34ASimilar project development processenvironmental clearance activitiesTables and matrix summaries of design elements, design decisions, and resources/software/tools availableevaluate the performance effects of design decisionsUpdated performance categoriesconsistent with broader, national performance-based transportation decision making effortsSpecific recommended performance measurescapture panel prioritiesmore recent completed research
11 Presentation Outline Project Background and Overview Information GatheringProject Work PlanNCHRP Report
12 Project Work Plan – Develop NCHRP Report 15-34A DeliverablesAnnotated Outline of the NCHRP Report 15-34ADraft Report documentsFinal Report documentsNCHRP Report 15-34ASupplemental Research Materials ReportKey ComponentsCoordinate with the panel to receive inputConsider past information gatheredIncorporate new research material available
13 Presentation Outline Project Background and Overview Information GatheringProject Work PlanNCHRP Report
14 NCHRP 15-34A ReportPart A: Basis and Knowledge for Performance Based Analysis in Geometric Design of Highways and StreetsChapter 1 through 4 OverviewPart B: Applications Guidance for Conducting Performance Based AnalysisChapter 5 - FrameworkChapter 6 - Project Examples
15 NCHRP 15-34A Report Part A Part B Chapter 1 – Introduction Chapter 2 – OverviewChapter 3 – Identify Project OutcomesChapter 4 – Geometric Design ElementsPart BChapter 5 – Process FrameworkChapter 6 – Case Studies/Project Examples
17 Chapter 1 - Introduction Role of performance-based analysis in transportation activitiesRole and value in geometric design of highways and streetsGuiding PrinciplesIntended outcomesConnect to project development processPerformance measures of design decisions
18 Chapter 1 - Introduction Fundamental model of the approach
19 Chapter 1 - Introduction Performance-based analysis of geometric designprinciples-focused approach that looks at the outcomes of design decisions as the primary measure of design effectiveness.Identifying project intended outcomesbasis for evaluating performanceGeometric design performanceInfluences whether a project achieves intended outcomes
21 Chapter 2 – OverviewOverview of geometric design decisions
22 Chapter 2 – OverviewRelationship between project-level and performance measures
23 Chapter 2 - OverviewGeometric design and the project development stagesPlanning Studies – not includedAlternatives Identification and EvaluationProject initiation, purpose and need, traffic analyses, preliminary alternatives, public outreach, technical studies, cost/benefit evaluations, refined analyses, selected alternative(s).
24 Chapter 2 - OverviewGeometric design and the project development stages - continuedPreliminary DesignHorizontal and vertical alignment, typical sections, grading plans, structures, traffic/ITS, signing and striping, illumination, and utilities.Final DesignConstruction
25 Chapter 2 – OverviewGeometric design and environmental evaluations and clearanceProject ScopingPurpose and NeedAlternatives AnalysisEffected EnvironmentEnvironmental ConsequencesMitigation
27 Chapter 3 – Identify Project Outcomes Fundamentally: Who are we serving?Who are we serving?identifying the key road users and stakeholders for a given project and project contextWhat are we trying to achieve?identifying and articulating the core desired outcomes from the project
28 Chapter 3 – Identify Project Outcomes Defining Project Performance – Goals and MeasuresMoving Ahead for Progress in the 21st Century Act (MAP-21)Congestion ReductionInfrastructure ConditionEnvironmental SustainabilityFreight Movement and Economic VitalityReduced Project Delivery DelaysSafetySystem ReliabilityUS DOT’s Strategic Plan forEconomic competitivenessEnvironmental sustainabilityLivable communitiesOrganizational excellenceSafetyState of good repair
29 Chapter 3 – Identify Project Outcomes Geometric Design Performance CategoriesAccessibilityability to approach a desired destination or potential opportunity for activity using highways and streets (including the sidewalks and/or bicycle lanes).Mobilityability to move various users efficiently from one place to another using highways and streets.Quality of Servicethe perceived quality of travel by a road user.Reliabilityconsistency of performance over a series of time periods.Safetyexpected frequency and severity of crashes occurring on highways and streets.
30 Chapter 3 – Identify Project Outcomes Role and Influence of Geometric Design FeaturesPerformance CategoryDefined Role/Influence of Geometric Design FeaturesWellDocumentedModerate DocumentationLimited DocumentationAccessibilityXMobilityReliabilitySafetyQuality of Service
31 Chapter 3 – Identify Project Outcomes Geometric Design Decisionsconsider overall intended project outcomes, project performance, and transportation performance.How do the features or qualities of the features influence performance measures related to accessibility, mobility, quality of service, reliability, and safety?may have incremental and cumulative effectsdiscrete choices may impact broader conceptssustainability, economic competitiveness, or livabilityidentifying project design controlsleads to appropriate design criteria to meet those design control needs
32 Chapter 3 – Identify Project Outcomes Project Design Controls and InfluencesSpeed concepts and design decisionsSight distance conceptsDesign choices for segments and nodes
33 Chapter 3 – Identify Project Outcomes Design choices for segmentsExample Design Decisions for SegmentsAccess points and densityDesign speed and target speedHorizontal alignmentNumber of travel lanesSidewalk and pedestrian facilitiesBicycle accommodation featuresTransit accommodation featuresDesign vehicle accommodationMedian provisionsTravel lane widthsAuxiliary lane widthsType and location of auxiliary lanesShoulder widthShoulder typeLane and shoulder cross slopesSuperelevationRoadside design featuresRoadside barrierMinimum horizontal clearanceMinimum sight distanceMaximum gradeMinimum vertical clearanceVertical alignmentBridge cross sectionBridge length/terminiRumble strips
34 Chapter 3 – Identify Project Outcomes Design choices for nodesExample Design Decisions for Nodes - Intersections and InterchangesIntersection form, control type, and featuresInterchange form and featuresDesign speed and target speedNumber and types of lanesSidewalk and pedestrian facilitiesBicycle accommodations facilitiesTransit accommodations facilitiesSpecial/vulnerable user treatmentsDesign vehicle accommodationsTraffic islandsLane widthsAuxiliary lane lengthsShoulder width and compositionApproach or ramp cross sectionHorizontal alignment of approaches or rampMainline ramp gores and terminalsCross road ramp terminalsVertical alignment of approaches or rampAuxiliary lane terminals and transitionsPavement cross slope and superelevationIntersection sight distanceMedian opening configurationCurve tapers & radiiRamp roadsideRamp barriers
36 Chapter 4 – Geometric Design Elements IntroductionSummarize critical or high priority known relationships between design elements and performanceDocument the general relationshipIdentify possibly performance trade-offsPresent resources and tools that can be used
37 Chapter 4 – Geometric Design Elements OverviewKey ResourcesAASHTO’s Highway Safety Manual (HSM)2010 Highway Capacity Manual (2010 HCM)Transit Capacity and Quality of Service Manual, 2nd Edition (TCQSM)FHWA’s Speed Concepts: Informational GuideDraft 2010 HSM chapters for freeways and interchanges (NCHRP Project 17-45)Interactive Highway Safety Design Model (IHSDM)
38 Chapter 4 – Geometric Design Elements Overview - NotationsEach characteristic/decision – performance measure category combination is classified as:Expected direct effectExpected indirect effectNo expected effect
39 Chapter 4 – Geometric Design Elements Overview - NotationsSecondary notation classifies each relationship as one of the following :The relationship can be directly estimated by existing performance prediction tools;The relationship can be indirectly estimated using more than one existing tool or supplemental calculations;The relationship cannot be estimated by existing tools; orNot applicable (i.e., the relationship does not exist).
40 Chapter 4 – Geometric Design Elements Expected relationships between geometric design elements and performance categoriesSegmentsNodes – Intersections and Interchanges● = expected direct effect□ = expected indirect effect-- = expected not to have an effect* = relationship can be directly estimated by existing performance prediction tools◊ = relationship can be indirectly estimated using more than one existing toolx = relationship cannot be estimated by existing tools
41 Chapter 4 – Geometric Design Elements Segments Segment Geometric Elements/CharacteristicsAccessibilityMobilityQuality of ServiceReliabilitySafetyAccess points and density●*□◊Design speed and target speed--□*Horizontal alignment●◊Number of travel lanesSidewalk and pedestrian facilities●□x●xBicycle accommodation featuresMedian provisionsTravel lane width(s)Auxiliary lane width(s)Type and location of auxiliary lanesShoulder width(s) and compositionShoulder type(s)Lane & shoulder cross slopesSuperelevationRoadside design featuresRoadside barriersMinimum horizontal clearancesMinimum sight distanceMaximum grade(s)Minimum vertical clearancesVertical alignment(s)Bridge cross sectionBridge length/ terminiRumble strips
42 Chapter 4 – Geometric Design Elements Nodes – Intersections Intersection Geometric Elements/CharacteristicsAccessibilityMobilityQuality of ServiceReliabilitySafetyIntersection form, control type, and features●◊●*□xNumber and types of lanesSidewalk and pedestrian facilities●xBicycle accommodation facilitiesDesign vehicle accommodationsTraffic islandsLane widthsAuxiliary lane terminals and transitionsShoulder width and compositionHorizontal alignment of approachesVertical alignment of approachesPavement cross slope and superelevation--Intersection sight distanceMedian opening configurationCurve tapers and radii
43 Chapter 4 – Geometric Design Elements Nodes – Interchanges Interchange Geometric Elements/CharacteristicsAccessibilityMobilityQuality of ServiceReliabilitySafetyInterchange form and features●◊●x□x●*Sidewalk and pedestrian facilitiesBicycle accommodation facilitiesAuxiliary lane lengthsHorizontal alignment of rampVertical alignment or rampPavement cross slope and superelevation--Ramp cross sectionMainline ramp gores and terminalsRamp roadsideRamp barriersCross road ramp terminals
44 Chapter 4 – Geometric Design Elements Geometric Design Decisions and PerformanceAccessibilityability to approach a desired destination or potential opportunity for activity using highways and streets (including the sidewalks and/or bicycle lanes).Mobilityability to move various users efficiently from one place to another using highways and streets.Quality of Servicethe perceived quality of travel by a road user.Reliabilityconsistency of performance over a series of time periods.Safetyexpected frequency and severity of crashes occurring on highways and streets.
45 Chapter 4 – Geometric Design Elements Tables summarize the design elements/decisions and their relationship to performance measures from each of the transportation performance categoriesKey ResourcesAASHTO’s Highway Safety Manual (HSM)2010 Highway Capacity Manual (2010 HCM)Transit Capacity and Quality of Service Manual, 2nd Edition (TCQSM)FHWA’s Speed Concepts: Informational GuideDraft 2010 HSM chapters for freeways and interchanges (NCHRP Project 17-45)Interactive Highway Safety Design Model (IHSDM)NCHRP Report 687, Guidelines for Ramp and Interchange SpacingNCHRP 672, Roundabouts: An Informational Guide, 2nd Edition
46 Chapter 4 – Geometric Design Elements Accessibility Facility TypePerformance MeasureDefinitionGeometric Design ElementsBasic RelationshipPotential Performance TradeoffsSegmentDriveway DensityNumber of driveways per mileAccess points and densityHigher density of driveways associated with higher motor vehicle accessDegrade bicycle LOS, Increase crash likelihood, Increase average travel speedUrban/ Suburban SegmentTransit stop spacingDistance between transit stops along a roadway segmentTransit accommodation featuresHigher frequency increases access for transit ridersIncreases transit travel time and may degrade mobility for other vehicle modesPresence of Pedestrian FacilityPresence of a sidewalk, multiuse path or shoulderSidewalk and pedestrian facilitiesGreater connectivity and continuity of pedestrian network increases access for pedestriansImplementing pedestrian facilities in a constrained environment may require removing capacity or parking for vehicle modePresence of Bicycle FacilityPresence of bicycle lanes, multiuse path, or shoulderBicycle accommodation featuresGreater connectivity and continuity of bicycle network increases access for bicyclistsImplementing bicycle facilities in a constrained environment may require removing capacity or parking for vehicle mode
47 Chapter 4 – Geometric Design Elements Mobility Facility TypePerformance MeasureDefinitionGeometric Design ElementsBasic RelationshipPotential Performance TradeoffsSegmentAverage Travel TimeThe mean amount of time it takes a roader user to travel from one point to another point along a roadway segment.Number of travel lanesIncreased vehicle lanes decrease average travel time for autos and increases vehicle speed.Degrades quality of service for pedestrians and bicyclists.Degrade mobility for pedestrians and bicyclists.Higher vehicle speeds are associated with higher severity crashes.Inferred speedThe maximum speed for which all critical design- speed-related criteria are met at a particular location.Horizontal alignment, vertical alignment, and cross- sectionHigher inferred speeds associated with higher free flow speeds and higher mobility.Higher vehicle speeds are also associated with higher severity crashes.Two-Lane SegmentAverage percent time spent followingThe average percent of total travel time that vehicles must travel in platoons behind slower vehicles due to an inability to pass.Horizontal and vertical alignment, sight distance, Type and location of auxiliary lanesIncreased opportunities to pass slow moving vehicles reduces percent time spent following, providing a passing lane can reduce crashes.Increase vehicle speeds, increase potential for higher severity crashes.
48 Chapter 4 – Geometric Design Elements Mobility Facility TypePerformance MeasureDefinitionGeometric Design ElementsBasic RelationshipPotential Performance TradeoffsFreewaySegmentSpeedThe freeway speed down stream of an entrance ramp and before an exit ramp or another entrance rampRamp spacing dimensions as defined in NCHRP Report 687.Use of downstream auxiliary laneAt relatively high exit ramp volumes, ramp spacing affects freeway speedsDecreased freeway speeds are possible with decreased ramp spacing.An auxiliary lane may improve freeway speedsIntersectionDelayAverage control delay experienced by road users at an intersection.Intersection form, control type, and features, Number and types of lanesLower control delay for any road user improves mobility for that modeOften tradeoffs between delay experienced by different modes depending on the type of traffic control present.Volume to Capacity (v/c) RatioThe ratio of volume present or forecasted and the available capacity at the intersection.Increased vehicle capacity associated with lower v/c ratios.Degrades quality of service for pedestrians and bicyclists.Degrade mobility for pedestrians and bicyclists.
49 Chapter 4 – Geometric Design Elements Quality of Service Facility TypePerformance MeasureDefinitionGeometric Design ElementsBasic RelationshipPotential Performance TradeoffsUrban/ Suburban SegmentPedestrian LOSA letter grade associated with the quality of travel experience for a pedestrian. Based on HCM methodology.Sidewalk and pedestrian facilities, width of pedestrian lanes, buffer from vehicle traffic, driveway density, crossing frequencyIncreasing width of pedestrian facility, increasing distance from vehicle traffic, decreasing driveway density, and increasing opportunities to cross a street improves pedestrian LOSMeeting performance metrics for pedestrians may degrade travel quality for other modes – e.g., on-street parking improves pedestrian LOS and degrades bicycle LOSUrban/ Suburban IntersectionsCrossing distance, traffic control delayDecreasing pedestrian crossing distance and delay to cross a street improves pedestrian LOSMeeting performance metrics for pedestrians may degrade travel quality for other modes
50 Chapter 4 – Geometric Design Elements Quality of Service Facility TypePerformance MeasureDefinitionGeometric Design ElementsBasic RelationshipPotential Performance TradeoffsUrban/ Suburban SegmentBicycle LOSA letter grade associated with the quality of travel experience for a bicyclist. Based on HCM methodology.Bicycle accommodation features, physical separation from motor vehicle traffic, access points and density, on street parkingIncreasing width of bicycle facility, decreasing driveway density, increasing separation from moving vehicle traffic, and removing on-street parking improves bicycle LOSMeeting performance metrics for bicyclists may degrade travel quality for other modesUrban/ Suburban IntersectionsTraffic control delayDecreased delay for bicyclists increases quality of travel experience
51 Chapter 4 – Geometric Design Elements Quality of Service Facility TypePerformance MeasureDefinitionGeometric Design ElementsBasic RelationshipPotential Performance TradeoffsUrban/ Suburban Segments and IntersectionsTransit LOSA letter grade associated with the quality of travel experience for a transit rider. Based on HCM methodology.Transit accommodations facilities (presence of transit only lane, bus pull out areas, bus merge/diverge lanes, bus queue jump lanes)Providing bus only lane, queue jump lanes, merge/diverge lanes decreases bus travel time and improves transit rider quality of travelIncorporating transit only features often comes at the expense of providing additional auto or bicycle capacity or treatmentsAuto LOSNumber and duration of stops along an urban/suburban corridor.Number of travel lanes, intersection form, control type, and featuresReducing the number of stops and duration of stops along a corridor improves auto MMLOSIncreased vehicle lanes and speeds degrades pedestrian and bicycle MMLOSIntersections and SegmentsLarge Vehicle Turning and Off- Tracking CharacteristicsAbility and ease with which large vehicles are able to physically move through an intersection or along a segmentCurve radii, curb radii, lane widthGenerally larger curve radii, larger curb radii and wider vehicle lanes enable easier navigation for larger vehiclesIncreasing curve radii, curb radii, and lane width often degrade pedestrian and bicycle MMLOS due to the longer crossing distances
52 Chapter 4 – Geometric Design Elements Reliability On-going research to develop performance measures to connect reliability to specific geometric design elementsVariation in travel time and variation in speed are two more common performance measuresThere are no clear performance measures available to easily integrate into design decisionAdditional reliability resources:SHRP 2 L07: Evaluation of Cost-Effectiveness of Highway Design Features (9)SHRP 2 L08: Incorporation of Travel Time Reliability into the Highway Capacity Manual (10)SHRP 2 L09: Incorporation of Non-recurrent Congestion Factors into the AASHTO Policy on Geometric Design (11)
53 Chapter 4 – Geometric Design Elements Reliability There are a number of design considerations that can be applied to highways and streets. These include the following tradeoffs:Mobility gained in implementing peak period hard shoulder running on a freeway segments and risk associated with a disabled vehicle during the peak period.Congestion pricing strategies on freeway segments to improve reliability and potential equity implications for lower income households.Ramp metering strategies to preserve the quality of mainline traffic flow while at the expense of degrading mobility on adjacent local streets.Implementing transit signal priority, bus only lane and/or queue jumps for transit vehicles along an urban corridor to improve the reliability of bus service with the potential impact of degrading mobility for side street vehicle traffic.Implementing concrete median barriers with heights that eliminate distractions from incidents on opposing roadway lanes (“rubbernecking”) and the potential safety performance degradation by introducing a fixed object.
54 Chapter 4 – Geometric Design Elements Safety Facility TypePerformance MeasureDefinitionGeometric Design ElementsBasic RelationshipPotential Performance TradeoffsRural two-lane segmentsCrash frequency and severityExpected number of and severity of crashesHorizontal alignment, shoulder width and composition, shoulder type, lane width, type and location of auxiliary lanes, rumble strips, roadside design features, lighting, two-way left turn lane, gradeSee HSMSome safety improvements reduce mobility, reduce access (e.g., reducing driveway density), or negatively impact another performance measure.Rural two-lane intersectionIntersection form, control type, and features, number and types of lanes, lighting, skewRural multilane segmentsShoulder width and composition, shoulder type, lane width, lane and shoulder cross slopes, median provisions, lighting, two- way left turn laneRural multilane intersection
55 Chapter 4 – Geometric Design Elements Safety Facility TypePerformance MeasureDefinitionGeometric Design ElementsBasic RelationshipPotential Performance TradeoffsUrban/suburban segmentsCrash frequency and severityExpected number of and severity of crashesBasic cross-section, , access points and density, fixed object density, median provisions, on- street parkingSee HSMSome safety improvements reduce mobility, reduce access (e.g., reducing driveway density), or negatively impact another performance measure.Urban/suburban intersectionIntersection form, control type, and features, number and types of lanes, signal phasingFreeway SegmentsLane width, shoulder width and composition, ramp spacing, use of auxiliary lanes, ramp entrance/exit configurationsSee NCHRP ReportInterchangeInterchange form and features, number and types of lanes, horizontal alignment, cross section, roadside
56 Chapter 4 – Geometric Design Elements Opportunities to Expand Performance-Based AnalysisA key fundamental concept in performance-based analysis to inform design decisions is geometric sensitivity.Geometric sensitivityThe degree to which varying the dimensions related to a geometric element has an impact on performance.A relationship that shows an expected impact on some aspect of transportation performance as a direct result of a geometric design decision.Level of sensitivityamount of the impacthighly sensitivenumber of travel lanes versus passenger car mobilityless sensitivelane width and average travel speedCertain relationships are sensitive only for certain ranges of geometric dimensions.
57 Chapter 4 – Geometric Design Elements Opportunities to Expand Performance-Based AnalysisNCHRP Report 687, Guidelines for Ramp and Interchange Spacing
60 Chapter 5 – Process Framework Project InitiationProject Contextexisting site constraintscurrent performancesurrounding land usesplanned improvementsanticipated form and functionIntended OutcomesClarity of the characteristics defining the current and desired future of the site;A clear and concise understanding of the primary project purpose; andA set of performance measures to be used to evaluate a design’s impact on the desired project purpose.
61 Chapter 5 – Process Framework Concept DevelopmentGeometric InfluencesIdentify the geometric characteristics that influence a project’s performanceIdentify the geometric characteristics or decisions influenced by the desired performance of a project.Potential Solutions – specific awareness of the:Project contextIntended outcomesGeometric characteristics and decisions
62 Chapter 5 – Process Framework Evaluation and SelectionEstimated Project PerformanceSelecting the evaluation resourceFor the stage in the project development process.Applicable to the project contextFinancial FeasibilityTotal construction and maintenance costCost effectivenessBenefit/cost Ratio (B/C ratio)Interpreting Results
63 Chapter 5 – Process Framework SelectionAre the performance evaluation results making progress towards the intended project outcomes?Do the alternatives serve the target audience and achieve the desired objectives?Are there reasonable adjustments that can be made to the geometric design elements most significantly influencing project performance?Do the performance measures help differentiate between the alternatives?
64 Chapter 5 – Process Framework Environmental Review ProcessEnvironmental ChecklistThe 15-34A framework can be used to explore and consider project alternatives or adjustments to enable a project to be eligible for a Categorical Exclusion.Environmental AssessmentProject Initiation phase of the performance-based analysis framework can serve as a useful resource in developing a clear, sound, and concise project Purpose and Need statement.Concept Development and Evaluation and Selection phases of the framework are resources for developing alternatives that minimize the potential for environmental impacts.Environmental Impact StatementThe 15-34A framework can be beneficial to practitioners in developing a draft EIS, selecting a preferred alternative in the final EIS, and identifying the means to avoid and minimize environmental impacts.
66 Chapter 6 – Case Studies/Project Examples Case Studies include a range of projects for:Site - Area and Facility Type;Project Development Stage;Performance Categories, andProject Type.
67 Chapter 6 – Case Studies/Project Examples Case Study #Site - Area and Facility TypeProject Development StagePerformance CategoriesProject Type1US 21/Sanderson Road - Rural Collector (Two-Lane Highway)Alternatives Identification and EvaluationSafetyIntersection – Consider alternative intersection control to improve safety.2Richter Pass Road - Rural CollectorPreliminary DesignSafety, MobilitySegment – Consider alternative horizontal curve radii to improve safety while minimizing costs and maintaining appropriate speed.3Cascade Ave - Suburban/Urban ArterialSafety, Mobility, Reliability, Accessibility, Quality of ServiceCorridor – Retrofitting an existing auto-oriented urban arterial to incorporate complete street attributes. Focus on alternative street cross-sections.4SR 4 - Rural CollectorSafety, Reliability, Quality of ServiceSegment – Consider alternative shoulder widths and sideslopes to minimize impact to an environmentally sensitive area.527th Avenue - Urban Minor ArterialQuality of Service, Safety, AccessibilitySegment – Alignment and cross-section considerations for new urban minor arterial being constructed to entice employers to a newly zoned industrial area.6US 6/Stonebrook Road - Rural InterchangeInterchange - Converting an at-grade intersection to a grade-separated interchange. Focus on selecting the appropriate interchange form and location
68 Case Study #1 – US 21/Sanderson Road Alternatives identification and evaluation stage of an intersection projectRural two lane highway (i.e., rural arterial)Intended outcome - improve safetyPerformance category – safetyuses expected crash frequency as the primary performance metricThe learning objectives of this case study include:Illustrating the process of applying performance-based analysis;Demonstrating the use of resources beyond typical design manuals within the project development process; andIllustrating how a financial feasibility assessment can inform project selection.
69 Case Study #1 – US 21/Sanderson Road Project Initiation - Project Context Intersection CharacteristicsRural, two-lane highway (US 21)Two-way stop controlled intersectionPrimary entrance to a tribal reservationUS 21 Highway - Regional east-west connectionAgricultural, undeveloped, wetlands, and low density residentialAADT is approximately 7700 vehicles per dayPosted speed is 55 mph, the 85th percentile speed is 58 mphLimited to no pedestrian or bicycle activityIntersection operational level of service (LOS) is LOS BSafety Data -Several fatal and serious injury crashes - Past 5 years55% were angle or turning crashes26% were rear-end crashesFailure to yield right-of-way (26% of crashes) and excessive speed (16% of crashes)Incremental solutionsadding illuminationAdding left-turn and right-turn lanes on US 21.
70 Case Study #1 – US 21/Sanderson Road Project Initiation - Intended Outcomes Tribe and the State Department of Transportation (DOT)Initiated a study to identify additional safety projectsReduce the number and severity of crashesEnhance the intersection as the gateway to their communityAccommodate a full range of motorists – agricultural equipment, logging trucks, local residents and visitors.Performance category - safety
71 Case Study #1 – US 21/Sanderson Road Concept Development Design elements related to crash frequency/severityPerformance TargetRelated Design ElementsRelated Design ConsiderationsReduce Total Number of Crashes; Reduce Severity of CrashesIntersection ControlTwo-way stop controlledAll-way stop controlledTraffic SignalRoundaboutIntersection Design FeaturesLeft-Turn LanesRight-Turn LanesPresence of LightingVisibility of IntersectionIncrease Intersection Awareness/VisibilityCross-Sectional Elements on Intersection ApproachLane WidthRumble StripsMedian (Painted or Splitter Island Type)Decrease Vehicle Speed on Intersection ApproachAlignment on Intersection ApproachRoadway curvatureSight DistanceAdvanced Signing
72 Case Study #1 – US 21/Sanderson Road Concept Development The project team identified the following groupings of alternatives to explore:Alternative intersection control;Advanced signing and pavement markings; andChanges in roadway cross-sectional features.
73 Case Study #1 – US 21/Sanderson Road Potential Solutions Potential intersection configurations - to make the intersection more visible and more clearly identifiable as the main intersection to access the tribal land.Implementing lane narrowingConstructing a Single-Lane Roundabout;Installing a Traffic SignalWay-finding signs and landscapingResources UsedAASHTO Green BookNCHRP Report 672 Roundabouts: An Informational Guide, Second EditionFHWA’s Low Cost Safety Concepts for Two-Way Stop Controlled, Rural Intersections on High-Speed Two-Lane, Two-Way RoadwaysNCHRP Report 613 Guidelines for the Selection of Speed Reduction Treatments on High-Speed Intersections
74 Case Study #1 – US 21/Sanderson Road Potential Solutions Solution Development – Single Lane Roundabout
75 Case Study #1 – US 21/Sanderson Road Potential Solutions Design Decisions – Single Lane RoundaboutAppropriate sizeposted speed on US 21design vehiclesanticipated turning movement volumesNumber of entry and exit lanes on each approachEntry and exit curve radiiestimated entry, circulating and exiting vehicle speedsAppropriate length of the splitter islands on US 21 to help make the intersection visible and support appropriate speed reduction from the roadway segment to the roundabout entry.Resource - NCHRP Report 672 Roundabout Informational Guide, Second Edition
76 Case Study #1 – US 21/Sanderson Road Potential Solutions Solution Development – Traffic Signal
77 Case Study #1 – US 21/Sanderson Road Potential Solutions Design Decisions – Traffic SignalAppropriate length of the approach medians on US 21 to help make the intersection visibleNumber of lanes and lane arrangement based on anticipated turning movement volumesAppropriate curve radii based on design vehiclesAppropriate taper lengths and deceleration lane lengths based on posted speed
78 Case Study #1 – US 21/Sanderson Road Evaluation and Selection Primary intent of the projectreduce the frequency and severity of crashesSecondary considerationincorporate way-finding and gateway treatments at the intersectionPerformance evaluation and financial feasibilityevaluating safety effectiveness as related to the likelihood of reducing crash frequency and severity
79 Case Study #1 – US 21/Sanderson Road Evaluation and Selection Estimating PerformanceDesign Elements Related to Crash Frequency/SeverityPerformance TargetRelated Design ElementsRelated Design ConsiderationsTools or Resources to Evaluate PerformanceReduce Total Number of Crashes; Reduce Severity of CrashesIntersection ControlTwo-way stop controlledAll-way stop controlledTraffic SignalRoundaboutHighway Safety Manual, Chapter 10 and Chapter 14 (5)Supporting Software Tools: HiSafe; IHSDMIntersection Design FeaturesLeft-Turn LanesRight-Turn LanesPresence of LightingVisibility of IntersectionsFHWA’s Low Cost Safety Concepts for Two-Way Stop Controlled, Rural Intersections on High- Speed Two-Lane, Two-Way Roadways (3)NCHRP Report 613 (4)
80 Case Study #1 – US 21/Sanderson Road Evaluation and Selection Estimating PerformanceDesign Elements Related to Crash Frequency/SeverityPerformance TargetRelated Design ElementsRelated Design ConsiderationsTools or Resources to Evaluate PerformanceIncrease Intersection Awareness/VisibilityCross-Sectional ElementsLane WidthRumble StripsMedian (Painted or Splitter Island Type)FHWA’s Low Cost Safety Concepts for Two-Way Stop Controlled, Rural Intersections on High- Speed Two-Lane, Two-Way Roadways (3)NCHRP Report 613 (4)Decrease Vehicle Speed on Intersection ApproachCross-Sectional Elements on Intersection ApproachAlignment on Intersection ApproachRoadway curvatureSight DistanceAdvanced Signing
81 Case Study #1 – US 21/Sanderson Road Evaluation and Selection Incorporating Financial Feasibilityidentify the relative cost effectiveness of each alternativeLocation - SolutionExpected Crashes/ YearEstimated Percent Reduction# of Crashes Mitigated/YearDesign Life (Years)Planning Level Cost Estimate$/Crash Mitigated Over Design LifeSanderson Road Intersection TWSC- FHWA Lane Narrowing2.231%0.75$45,000$13,196Sanderson Road Intersection TWSC - FHWA Splitter Island68%1.5$112,500$15,040Sanderson Road- Single Lane Roundabout71%1.620$3.15 million$100,832Sanderson Road - Traffic Signal36%0.8$5.61 million$354,167
82 Case Study #1 – US 21/Sanderson Road Selected Alternative Tribe and DOT decided to implement a roundabout at the US 21/Sanderson Road intersectionway-finding and gateway treatmentsRoundabout AlternativeLong-term potential for reducing the intersection crash frequency and severityOpportunities for gateway treatments at and on approach to the intersectionCreate definitive visual cues and changes in roadway geometry to capture motorists’ attention and aid in reducing approach speeds.
83 Case Study #3 – Cascade Avenue Reconstructing an existing auto-oriented urban arterialcomplete street attributesalternative street cross-sectionsLocal business owners would like to see the corridor revitalizedThe learning objectives of this case study include:Incorporating performance measures and decisions related to accommodating multiple modes;Illustrating tradeoffs between modes considering measures beyond mobility; andCapturing considerations and tradeoffs within a constrained physical environment.Geometric design performance categories of quality of service for multiple modes, safety, access, reliability and mobility.
84 Case Study #3 – Cascade Avenue Project Initiation - Project Context Urban arterialNorth-south connection between the downtown and universityAADT volume 22,000 vehicles per dayThree different fixed transit routes - 45% of riders within the CityFrequently used by bicyclistsPosted speed on Cascade Avenue is 35 mph
85 Case Study #3 – Cascade Avenue Intended Outcomes Target audienceBusiness community stakeholdersTransit riders, pedestrians and bicyclistsLocal residents and existing motoristsIntent of the StudyImprove the road user experienceProvide access to road users not previously servedEnhance the economic vitality and activity of the streetPerformance categoriesquality of service, safety, accessibility, reliability, and mobilityPerformance measuresQuality of Service – Multimodal Level of Service (MMLOS)Safety – Crash frequency and conflict pointsAccessibility – Type and presence of facilities and transit service characteristicsMobility – Average travel timeReliability – Consistency in travel time
86 Case Study #3 – Cascade Avenue Concept Development Roadway cross-sectional elements were selected as the primary geometric elements likely to influence the performance measuresLane widthNumber of automobile through lanesBicycle facility presence and typeSidewalk widthLandscaped buffer between sidewalk and travel lanesOn street parkingBus only lanesCentral roadway median
87 Case Study #3 – Cascade Avenue Potential Solutions The four basic alternatives :Alternative 1 – Existing cross-section oriented towards serving automobilesBaseline for comparisonAlternative 2 – Transit oriented cross-sectionServe transit vehicles and ridersAlternative 3 – Bicycle and pedestrian oriented cross-sectionServe bicyclists and pedestriansAlternative 4 – Hybrid of transit, bicycle and pedestrian features.Serve transit, bicyclists and pedestriansResources Used to Develop SolutionsUrban Streets Design Guide published by the National Association of City Transportation Officials (NACTO)NACTO’s Urban Bikeway Design GuideAASHTO Guide for the Development of Bicycle Facilities, 4th EditionCity’s local design guides and standards
88 Case Study #3 – Cascade Avenue Potential Solutions – Solution Development Each alternative cross-section has a modal emphasis in contrast to the existing auto-oriented cross-sectionA common element among the alternatives is the lack of on-street parking.More pedestrian spaceCity’s goals and policies focus on projects serving person-trips rather than only auto tripsCreates concern for on-street parking in adjacent residential areasOther tradeoffs consideredallocating lanes for specific modes – Transit-only laneimprove mobility and reliability for transit ridersmore predictable operating conditionsnegatively impacts mobility (and potentially reliability) for automobilesProviding bicycle lanes and wider sidewalks for pedestriansAlternatives include a central landscaped mediandocumented safety benefits for autos and pedestriansSpace to implement landscaping to help improve the aesthetics of the corridor
89 Case Study #3 – Cascade Avenue Potential Solutions – Primary Alternative Evaluation
90 Case Study #3 – Cascade Avenue Potential Solutions – Primary Alternative Evaluation
91 Case Study #3 – Cascade Avenue Potential Solutions – Primary Alternative Evaluation Common elements across the alternativesFalls within the existing 82 feet of right-of-way widthno additional right-of-way requiredRequires changing the existing curb locationsrevised storm water management and drainage along the corridorReduces the capacity for automobilesTwo-lanes in each direction to one-lane in each directionRemoves on-street parkingIncreases sidewalk width for pedestriansDifferentiating factors across the alternativesAmount of space designated for bicyclistsPresence of a central medianPresence of a physical buffer for pedestrians and bicyclists from motor vehiclesType of space allocated for transit vehiclesAdditional critical considerationsLogistics of truck loading and unloading for the businessesDefining transition areas on approach to intersections or major drivewaysManage conflict areas within transit-only and/or bicycle lanesTraffic control and lane configurations at intersections
92 Case Study #3 – Cascade Avenue Evaluation and Selection Performance categoriesSafetycrash frequency, crash severity, and conflict pointsMobilityaverage travel timeReliabilityVariation in travel timeAccessibilityType and facility presence and transit service characteristicsQuality of servicemultimodal level of service
93 Case Study #3 – Cascade Avenue Evaluation and Selection Estimating PerformanceSummary of ResourcesAlternativeSafetyMobilityReliabilityAccessibilityQuality of Service#1 – Existing ConditionHSM, Chapter 12HCM 2010Qualitative Assessment#2 – Transit OrientedHSM, Chapter 12 Principles#3 – Bicycle and Pedestrian Oriented#4 – Hybrid of Transit, Bicycle and Pedestrian
94 Case Study #3 – Cascade Avenue Evaluation and Selection Estimating Performance – SafetyAASHTO’s HSM methodologiesSafety performance for urban/suburban arterials roadway cross-sectionsCross-sections ranging from two-lane undivided to five-lanesEstimate the long-term annual safety performance of Cascade Avenue if no changes to the cross-section were made.Remaining features that cannot be evaluated using the HSMThe transit lanes present in Alternative 2 and 4;The buffered bicycle lane present in Alternative 3; andThe traditional bicycle lane in Alternative 4.Qualitative considerations based on the alternative’s ability to separate conflicting modes and provide protected space for vulnerable users.
95 Case Study #3 – Cascade Avenue Evaluation and Selection Estimating Performance – MobilityHighway Capacity Manual (HCM) 2010 methodologiesAverage travel time from one end of Cascade Avenue to the other.morning, mid-day and evening weekday periodsSaturday mid-day peak period.Travel time for motorists and transit vehicles
96 Case Study #3 – Cascade Avenue Evaluation and Selection Estimating Performance – ReliabilityOn-going research to develop performance measures and a means to strengthen the connection between reliability and geometric design decisionsCurrent approach for urban arterialsVariation in travel time is the best means for estimating relative consistency for motorists and transit riders on Cascade AvenueSimulated traffic operations along the corridor
97 Case Study #3 – Cascade Avenue Evaluation and Selection Estimating Performance – AccessibilityQualitative assessment of accesslow, moderate, or highpresence of facilities for specific modes and the transit service characteristics reflected in each alternative.
98 Case Study #3 – Cascade Avenue Evaluation and Selection Estimating Performance – Quality of ServiceMultimodal Level of Service (MMLOS) - HCM 2010Provides a letter grade A through F to indicate the quality of the travel experience from specific road users’ perspective.May result in one street cross-section having different quality of experiences depending on whether a person is walking, biking, taking transit or driving an automobile.Captures some of the benefits from project elements the HSM cannot; such as bicycle lanes.
99 Case Study #3 – Cascade Avenue Evaluation and Selection Performance Evaluation ResultsAlternativeSafetyMobility: Average Travel Time (min)Reliability: Variation in Travel TimeAccessibilityQuality of Service: MMLOS#1 – Existing ConditionPedestrianLow-DBicycleFTransit4.433.68 to 5.26ModerateAuto2.672.42 to 3.17HighA#2 – Transit OrientedCE4.403.68 to 4.76B3.433.35 to 3.60#3 – Bicycle and Pedestrian Oriented4.803.97 to 6.003.80 to 6.10#4 – Hybrid of Transit, Bicycle and Pedestrian4.383.65 to 4.783.453.32 to 3.56
100 Case Study #3 – Cascade Avenue Evaluation and Selection Incorporating Financial Feasibilityidentify the relative cost effectiveness of each alternativeAlternativeCost per MileAlternative #1 – Existing Condition$0Alternative #2 – Transit Oriented$1.4 millionAlternative #3 – Bicycle and Pedestrian Oriented$1.6 millionAlternative #4 – Hybrid of Transit, Bicycle and Pedestrian$1.0 million
101 Case Study #3 – Cascade Avenue Selected Alternative City and project stakeholders - Alternative 2provides improved safety, reliability, access, and quality of service for transit riders, pedestrians and bicyclists.Local business community - Alternative 3City plans to integrate Alternative 3 attributes into Alternative 2landscaping along the sidewalkscharacteristics to better serve bicyclists
102 NCHRP 15-34A Report Summary Performance-based analysis of geometric designprinciples-focused approach that looks at the outcomes of design decisions as the primary measure of design effectiveness.Geometric Design Performance CategoriesAccessibility, Mobility, Quality of Service, Reliability, SafetyProcess FrameworkProject Initiation – Project Context and Intended OutcomesConcept Development – Geometric Influences and Potential SolutionsEvaluation – Estimated Performance and Financial FeasibilitySelected Alternative
103 Presentation Outline Project Background and Overview Information GatheringProject Work PlanNCHRP Report
104 NCHRP 15-34A: Performance-Based Analysis of Geometric Design of Highways and Streets Questions?Brian Ray Erin Ferguson Richard J. Porter