Statewide Roundabout Guidance Chris Tiesler, PE Associate Engineer Michael Clements, PE Signal & Arterial System Manager
Agenda Background Three Tools Screening Tool Spreadsheet Tool Design Guidance Primer Case Study
Background State agencies with successful roundabout programs generally have Policy statement Process Tools Internally apply the intent of the policy Assist in performing assessments VDOT has a strong policy, but lacked a consistent process and tools necessary to adhere to its policy
Three Tools Screening Guidance Planning-level feasibility Spreadsheet Tool Compare control forms Go beyond operations Easy to use/maintain User Manual companion Design Guidance Primer Principle-based Resource http://www.virginiadot.org/info/faq-roundabouts.asp
Figure 1 Planning Level Daily Intersection Volumes (NCHRP Report 672 Exhibit 3-12) Tool #1: Planning-Level Screening Document Determine General Lane Needs 50,000 45,000 40,000 35,000 30,000 Double-lane roundabout may be sufficient (additional analysis needed) AADT 25,000 20,000 Single-lane roundabout may be sufficient (additional analysis needed) 15,000 10,000 5,000 Single-lane roundabout likely to operate acceptably Double-lane roundabout likely to operate acceptably 0 0% 10% 20% 30% 40% Left-Turn Percentage Planning Level Daily Intersection Volumes (NCHRP Report 672 Exhibit 3-12)
Figure 1 Planning Level Daily Intersection Volumes (NCHRP Report 672 Exhibit 3-12) Planning-Level Screening Right of Way Determine approximate footprint Roundabout Configuration Typical Design Vehicle Common Inscribed Circle Diameter Range* Mini-Roundabout SU-30 45 to 90 ft Single-Lane Roundabout B-40 90 to 150 ft WB-50 105 to 150 ft WB-67 130 to 180 ft Multilane Roundabout (2 lanes) WB-50 150 to 220 ft WB-67 165 to 220 ft Multilane Roundabout (3 lanes) WB-50 200 to 250 ft WB-67 220 to 300 ft * Assumes 90-degree angles between entries and no more than four legs. List of possible design vehicles not all-inclusive. Adapted from NCHRP Report 672 (Exhibit 6-9)
Figure 1 Planning Level Daily Intersection Volumes (NCHRP Report 672 Exhibit 3-12) Planning-Level Screening Approximate magnitude/size of roundabout and associated impacts can be initially judged Consider: Right of way Environmental impacts Utilities Topography
Figure 1 Planning Level Daily Intersection Volumes (NCHRP Report 672 Exhibit 3-12) Planning-Level Screening What other questions/factors should I consider? Network Interactions Consider site and surround intersection(s) in close proximity Intersection spacing? Adjacent traffic control related queuing characteristics Corridor considerations
Tool #2: Spreadsheet Tool Compares life-cycle costs of roundabout to traffic signal or stop-control across range of criteria Elements included: Safety Vehicular delay Operations and Maintenance Capital design and construction costs Right-of-way cost Elements not included: Emissions and fuel consumption Other qualitative elements
Key Takeaways Easy to use Requires basic information that is readily available Evaluate criteria beyond traffic operations à BETTER DECISIONS
What do I need? Opening year and design year ADTs Recent turning movement counts Operational analysis to determine: Turn lane requirements Control delay Basic geometric layout Historical crash data (optional) Preliminary cost estimate User is prompted for additional detail as needed (case-by-case) Assumptions can be made Straightforward inputs
Spreadsheet Format Four main input tabs Introduction MainENTRY AdjustSPF DelayENTRY Results tab Summary comparison Benefit/Cost ratio (if calculable/relevant)
Introduction Tab Provides spreadsheet navigation instructions Color Coding Orange cells indicate required data entry Blue cells indicate optional data entry Red text provides further instruction
MainENTRY Tab User-friendly drop list fields allow for easy scenario selection Non-applicable fields blocked out in gray
MainENTRY Tab
MainENTRY Tab Terminology ( Case ) only used in this spreadsheet Traditional intersection refers to stopcontrol or signal Scenarios Case 1: Existing Traditional Intersection vs. Proposed Roundabout Case 2: Proposed Traditional Intersection vs. Proposed Roundabout at Site of Existing Intersection Case 3: Proposed Traditional Intersection vs. Proposed Roundabout at New Site
MainENTRY Tab Existing Controls Traffic Signal Two-Way Stop Control All-Way Stop Control Field is not applicable for Case 3.
MainENTRY Tab Proposed Traditional Intersection Traffic Signal Two-Way Stop Control All-Way Stop Control Field is not applicable for Case 1.
MainENTRY Tab Required safety inputs are used to predict crash frequency
MainENTRY Tab Operations and Maintenance User enters Number of Luminaires Spreadsheet automatically includes other costs (signal maintenance for a signal, landscaping for roundabout, etc.) Capital Costs User must enter Spreadsheet does not provide average costs Default Unit Costs
Highway Safety Manual Content Part A Introduction and Fundamentals 1: Introduction 2: Human Factors 3: Fundamentals Part B Roadway Safety Management 4: Network Screening 5: Diagnosis 6: Select Countermeasures 7: Economic Evaluation 8: Prioritization 9: Safety Effectiveness Evaluation Part C Predictive Method 10: Two-Lane Rural Highways 11: Multilane Rural Highways 12: Urban and Suburban Arterials Part D Crash Modification Factors 13: Roadway Segments 14: Intersections 15: Interchanges 16: Special Facilities 17: Networks Glossary
AdjustSPF Tab Data entered uses HSM Part C CMFs to complete the SPF calculations Only fields for selected facility type are shown
DelayENTRY Tab
DelayENTRY Tab Enter the results of ops analysis from another program (Synchro, Sidra, HCS, etc.) Opening year and design year Use as many hours of day as you want Peak hours only is OK User can apply a typical or peak hour to multiple hours of the day Spreadsheet does not extrapolate to all hours of day
VDOT Spreadsheet Tool - Results Intersection Annual and Initial Capital Cost Comparison Annual Costs are itemized by: Safety Delay Operating and Maintenance Initial Capital is itemized by: Preliminary Engineering Right-of-Way and Utilities Construction
VDOT Spreadsheet Tool - Results Calculates the monetary safety and delay components of the intersection forms Compares ops/maintenance and initial capital costs expenditures Life Cycle Benefit/Cost Ratio
Spreadsheet Tool Summary Spreadsheet tool compares intersection control forms across wide range of criteria Operations Safety Costs Construction Operations/Maintenance (Life Cycle) Easy to use and maintain Supplements initial roundabout screening tool User Manual provides detailed information regarding methodologies
Design Guidance Primer Condensed design guidance for practitioners Emphasize key principles Planning Economic Evaluation Public Involvement Operations Safety Design Design Vehicle Splitter Islands Truck Apron Non-motorized Users Curbs/Drainage Traffic Control Devices Illumination Landscaping
Case Study - Hopkins Road/Kingsland Road
Case Study - Hopkins Road/Kingsland Road Existing TWSC intersection 4 legs Both roads suburban two-lane, two-way roads Hopkins Road 7,750 ADT (opening year) 11,290 ADT (design year) Kingsland Road 1,840 ADT (opening year) 2,120 ADT (design year) Evaluate traffic signal vs. single-lane roundabout
What do I need? Opening year and design year ADTs Recent turning movement counts Operational analysis to determine: Turn lane requirements Control delay Basic geometric layout Historical crash data (optional) Preliminary cost estimate User is prompted for additional detail as needed (case-bycase) Assumptions can be made Straightforward inputs
Why Evaluate Roundabout? 15 crashes in three years 11 angle crashes Five injury crashes One fatality
Hopkins Road/Kingsland Road
Hopkins Road/Kingsland Road - Results
Summary All three tools are now housed and available on VDOT s external Roundabouts website http://www.virginiadot.org/info/faq-roundabouts.asp Streamlines, enhances, and standardizes the consideration of roundabouts as prescribed by VDOT s policy Consideration of life cycle costs beyond initial capital costs Safety Operations/maintenance EASY TO USE!
Questions?