Statewide Roundabout Guidance

Transcription

1 Statewide Roundabout Guidance Chris Tiesler, PE Associate Engineer Michael Clements, PE Signal & Arterial System Manager

2 Agenda Background Three Tools Screening Tool Spreadsheet Tool Design Guidance Primer Case Study

3 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

4 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

5 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)

6 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 to 90 ft Single-Lane Roundabout B to 150 ft WB to 150 ft WB to 180 ft Multilane Roundabout (2 lanes) WB to 220 ft WB to 220 ft Multilane Roundabout (3 lanes) WB to 250 ft WB 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)

7 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

8 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

9 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

10 Key Takeaways Easy to use Requires basic information that is readily available Evaluate criteria beyond traffic operations à BETTER DECISIONS

11 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

12 Spreadsheet Format Four main input tabs Introduction MainENTRY AdjustSPF DelayENTRY Results tab Summary comparison Benefit/Cost ratio (if calculable/relevant)

13 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

14 MainENTRY Tab User-friendly drop list fields allow for easy scenario selection Non-applicable fields blocked out in gray

15 MainENTRY Tab

16 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

17 MainENTRY Tab Existing Controls Traffic Signal Two-Way Stop Control All-Way Stop Control Field is not applicable for Case 3.

18 MainENTRY Tab Proposed Traditional Intersection Traffic Signal Two-Way Stop Control All-Way Stop Control Field is not applicable for Case 1.

19 MainENTRY Tab Required safety inputs are used to predict crash frequency

20 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

21 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

22 AdjustSPF Tab Data entered uses HSM Part C CMFs to complete the SPF calculations Only fields for selected facility type are shown

23 DelayENTRY Tab

24 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

25 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

26 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

27 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

28 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

29 Case Study - Hopkins Road/Kingsland Road

30 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

31 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

32 Why Evaluate Roundabout? 15 crashes in three years 11 angle crashes Five injury crashes One fatality

33 Hopkins Road/Kingsland Road

34 Hopkins Road/Kingsland Road - Results

35 Summary All three tools are now housed and available on VDOT s external Roundabouts website 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!

36 Questions?