REGIONAL DESIGN INSTRUCTION

New York State Department of Transportation

Region One RDI 11-03 Roundabout Design Process

Approved by: __/s/ James P. Bridges____ _______ James P. Bridges, Regional Design Engineer

__/s/ Mark J. Kennedy____ _______ Mark J. Kennedy, Regional Traffic Engineer

Effective Date: February 23, 2011 Expires: February 23, 2016 Supersedes: None

Purpose The purpose of this RDI is to identify and discuss critical design issues related to the

design of intersection projects where a roundabout is being (or could be) considered as an intersection option and to establish a formal process the Region will follow to evaluate roundabout designs in the most efficient manner possible. This RDI requires that the appropriate people are involved early in the decision making process to ensure resource efforts are not expended on an inappropriate design.

This policy is needed because of the evolving nature of roundabout design and the Department’s desire to ensure consistency to the traveling public. The need for this policy will be re-evaluated in the future as roundabout design experience is greatly increased.

This RDI supplements guidance for roundabout intersection design provided in Chapters 5, 8, 11 & 18 of the Highway Design Manual (HDM), Engineering Instruction (EI) 00-21 and NCHRP’s publication titled, “Roundabouts: An Informational Guide – Second Edition” (Report 672). Designers should be aware that at the time this RDI was issued it was NYSDOT’s intent to rescind the Department’s current policy on roundabouts (EI 00-21) and adopt NCHRP Report 672 with some minor alterations/clarifications. Designers should determine what the Department’s current policy on roundabouts is prior to initiating design and, as appropriate, periodically throughout the design phase. This RDI is not intended to be an all encompassing policy. Designers should also consider other appropriate sources of information and guidance available to them for the design of roundabouts.

https://www.dot.ny.gov/portal/pls/portal/mexis_app.pa_ei_eb_admin_app.show_pdf?id=1621http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_672.pdfhttp://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_672.pdfhttps://www.dot.ny.gov/portal/pls/portal/mexis_app.pa_ei_eb_admin_app.show_pdf?id=1621https://www.dot.ny.gov/portal/pls/portal/mexis_app.pa_ei_eb_admin_app.show_pdf?id=1621

RDI 11-03 Page 2

Background

Since the late 1990’s roundabouts have become an additional option when considering solutions for a particular intersection. In fact, Section 5.9.1 of the HDM includes language about the consideration of roundabouts. It states, “…when a project includes reconstructing or constructing new intersections, a roundabout alternative is to be analyzed to determine if it is a feasible solution based on site constraints.” It goes on to state, “when the analysis shows that a roundabout is a feasible alternative, it should be considered the Department’s preferred alternative due to the proven substantial safety benefits and other operational benefits.”

Over the past several years, a number of roundabouts have been designed and constructed in the Region. These roundabouts have been monitored since they became operational. Some of these roundabouts (primarily the higher volume 2-lane roundabouts) are not functioning as well as originally intended. The following types of operational issues have been observed:

• Higher than anticipated accident rates, • Excessive approach speeds, • Failure to yield to traffic within the roundabouts, • Incorrect lane usage, • Improper lane usage for private ingress/egress points close to roundabouts, • Motorist noncompliance with approach signs and pavement markings.

Based on these observations and analysis of accident patterns, the Region determined that some of the most critical roundabout design parameters are entry angle (deflection), non-overlapping entry and exit paths on multi-lane roundabouts, approach speed, fastest vehicle paths (“racing lines”), sight distance, pavement markings and an appropriate level of signage. It is critical that designers understand the relationships between the various roundabout geometric elements and the resulting operation. Attention to detail is critical for the success of a roundabout project. The Region has concluded that the most effective way to address these types of operational issues on future designs is a formalized approach to the design and review process for roundabouts. To ensure the appropriate design parameters are considered and the appropriate parties are involved in the decision making process, the following, more comprehensive design process will be followed when a roundabout is being (or could be) considered as an intersection option. The focus of the process in the following section is generally on roundabouts. Until roundabouts become a standard intersection design, much like stop and signal controlled intersections currently are, following the steps outlined below will enable the Region as a whole to become more proficient in the design of roundabouts and will provide a means to ensure consistency on the transportation system.

RDI 11-03 Page 3

Policy

This policy applies to:

• All intersection designs in Region 1 on the State Highway system where a roundabout is being (or could be) considered as an intersection option. This includes projects initiated by municipalities or developers through the Highway Work Permit process.

• All local intersection projects administered by the Region where a roundabout is being (or could be) considered as an intersection option.

This policy will not be applicable to Short Term Accident Reduction (STAR) Projects, as outlined in RDI 07-02, or subsequent issuance, unless the Regional Traffic Engineer and the Regional Design Engineer agree that a roundabout should be investigated.

Definition of Terms Used in the Process Steps

• “Designer” - Throughout the process below the term “designer” implies the individual or group of individuals responsible for the progression of design. The Project Manager, Consultant Manager, Permit Engineer, or the Local Project Manager, as appropriate, will coordinate the steps within this RDI with the individual or entity responsible for the design.

• “Bicycle/Pedestrian Coordinator” – Throughout the process below the term “Bicycle/Pedestrian Coordinator” implies the individual(s) within NYSDOT Region 1 who, at the time of design, should be consulted on bicycle and pedestrian accommodations. The designer should contact the Landscape Architecture and Environmental Services Group at the appropriate time to identify the individual(s) that will be involved in this process.

Design Process Steps

The steps outlined below are not necessarily all inclusive. In unusual circumstances, elimination of some of the steps outlined below may be appropriate, provided there is consensus between the RDE, RTE and Regional Roundabout Coordinator. A diagram outlining the below steps is included in Appendix A.

1. Identify the candidate intersection. The candidate intersection will typically be

identified as part of the Department’s IPP/Scoping process.

2. Initial Screening a. Highway Design Manual (HDM) Roundabout Exceptions

Section 5.9.1 of the HDM lists exceptions to the requirement that a roundabout alternative be analyzed to determine if it is a feasible solution based on site constraints. These exceptions are where the intersection: - Has no current or anticipated safety, capacity, or other operational

problems. - Is within a well working coordinated signal system in a low-speed, <

50 mph (80 km/h), urban environment with acceptable accident histories.

https://www.dot.ny.gov/regional-offices/region1/repository/RDI%2007-02%20Short%20Term%20Accident%20Reduction%20STAR%20Projects%20(F.pdf

RDI 11-03 Page 4 - Is where signals will be installed solely for emergency vehicle

preemption. - Has steep terrain that makes providing an area, graded at 5% or less

for the circulating roadways, infeasible. - Has been deemed unsuitable for a roundabout by the NYSDOT Main

Office Intersection Design Squad [with Regional concurrence].

b. Traffic Volume As an additional initial screening criterion, the designer should consider the volume of traffic using the intersection. If the projected average annual daily traffic (AADT) entering the intersection for the design year is 45,000 vehicles/day or less, a roundabout could be considered further per the diagram below. Preliminary traffic volume and turn count information can be obtained from the Regional Planning Office.

Exhibit 3-12 in NCHRP’s publication titled, “Roundabouts: An Informational Guide – Second Edition”.

c. Scoping Meeting Discussion

The designer should initiate a discussion at the project’s Scoping Meeting to determine if there is a strong consensus on a proposed solution for the subject intersection(s). For this discussion to occur, many of the items listed in step 3, “Concept Development”, should be considered prior to the Scoping Meeting. The discussion at the Scoping Meeting should include a conversation related to:

• Potential cost and impacts of the various alternative intersection designs, balancing NYSDOT’s long-term transportation needs with the initial capital investment required to address the objectives of the project. Would a roundabout be the most cost effective solution?

• Has a roundabout been articulated as a favorable/unfavorable solution by the municipality and/or a Metropolitan Planning Organization (MPO)? If so, should documentation be developed

http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_672.pdf

RDI 11-03 Page 5 to justify to the municipality or MPO why a roundabout is/isn’t an appropriate alternative?

After considering all of the above initial criteria: • If a one or two lane roundabout is feasible, continue to step 3. • If a roundabout is not considered feasible, the designer will document the

reasoning to an appropriate level of detail in the Design Approval Document. In this case the designer should progress the remaining non-roundabout alternatives per HDM Section 5.9 and abandon this process.

3. Concept Development

The designer will: a. Request an accident analysis for the existing intersection. Review the

analysis and note any patterns of accidents and any recommended solutions offered by the Regional Traffic & Safety Group.

b. Identify the use of the existing intersection by pedestrians and bicyclists. c. Identify the design vehicle(s). d. Determine if the intersection is part of a Qualifying Highway on the

National Network of Designated Truck Access Highways or on an Oversized Vehicle Route. It is recommended the designer contact the Office of Modal & Security, Oversize/Overweight Permitting Section, in the Main Office for assistance.

e. Determine if the intersection is part of a linkage or corridor study and what recommendations were made regarding the intersection and/or adjacent roadways.

f. Model applicable intersection alternatives using appropriate methods such as the latest, approved version of SIDRA, per Engineering Bulletin 07-012, or subsequent issuance. This should include, at a minimum, appropriate roundabout and traditional stop and/or signal controlled intersection options. If the number of feasible options is expected to be excessive, it is suggested the designer attempt to eliminate impractical options prior to continuing this process.

i. Model ETC, ETC+10 and ETC+20 for all relevant peak periods (AM and PM peak, minimum). For Highway Work Permit Projects: Projects implemented through the Highway Work Permit process, with no public funds, will be required to consider ETC and ETC+10 only. If the results from the ETC+10 analysis would result in a significantly upgraded intersection (as compared to the ETC analysis), a discussion between NYSDOT, the developer, the developer’s designer and the municipality should take place to determine if: a) the upgraded intersection should be pursued (ETC+10), b) the minimum intersection should be pursued with provisions to expand in the future (ETC, but allowing for expansion to ETC+10 in the future), or c) the minimum intersection should be pursued (ETC). Also, a discussion regarding the funding mechanisms should take place for any upgraded intersection (items a or b).

ii. Identify the growth rates used. NYSDOT designers will obtain the growth rates from the Regional Planning Office. Growth rates

https://www.dot.ny.gov/portal/pls/portal/mexis_app.pa_ei_eb_admin_app.show_pdf?id=6762https://www.dot.ny.gov/portal/pls/portal/mexis_app.pa_ei_eb_admin_app.show_pdf?id=6762

RDI 11-03 Page 6 derived by consultant designers will need to be verified by NYSDOT’s Regional Planning Office.

iii. Provide classified turning movement volumes (for all intersection options).

iv. Provide a comparison and recommendation for the corridor or network. Include all pertinent software reports (such as LOS, queue lengths, delay, degree of saturation, etc.).

v. Identify the approximate year a single or double lane roundabout (as applicable) would likely fail/require expansion.

g. Identify the approach design speed for each approach leg. If the speed is greater or equal to 45 mph (70 km/h), the design must consider the addition of reverse curves on the approach, per Section 6.8.5.4 of NCHRP Report 672, Roundabouts: An Informational Guide – Second Edition.

h. Prepare conceptual drawings of each intersection option modeled. i. Traditional intersection options should be progressed in

accordance with HDM Section 5.9, Intersections at Grade. ii. Roundabout intersection options should be progressed in

accordance with the Department’s latest roundabout design guidelines and NCHRP Report 672, Roundabouts: An Informational Guide – Second Edition. When preparing conceptual drawings, among other things, the designer should consider the competing needs and placement of utility strips, signing and utility pole relocations. For instance, as a sidewalk approaches a roundabout, it is typically beneficial to taper the sidewalk away from the roundabout to allow ample room to accommodate signage within the utility strip.

The drawings should include existing features such as ROW/property lines, utilities, buildings, driveways, environmental constraints, drainage facilities and any other fixed objects.

i. Understand the potential impacts each intersection option has on ROW, utilities, the environment, future transportation plans, constructability, etc, and consider the effects any nearby intersections and/or private/commercial driveways might have on the operation of the intersection. Designers may wish to use RDI 10-04, or subsequent issuance, titled “Minor Intersection Design”, as a guide for the types of things to consider. Identify any potential impacts that might necessitate dismissal of any intersection options.

j. Estimate cost differences in all intersection options taking into account the potential impacts and mitigation.

k. Continue to step 4.

4. Concept Meeting a. The designer will hold a Concept Meeting with the following suggested

attendees: i. Regional Design Engineer,

ii. Regional Traffic Engineer, iii. Resident Engineer, iv. Design Supervisor, v. Regional Roundabout Coordinator,

vi. Main Office Intersection Design Squad Representative,

http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_672.pdfhttp://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_672.pdfhttp://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_672.pdfhttps://www.dot.ny.gov/regional-offices/region1/repository/RDI_10-04_Minor_Intersection_Design.pdf

RDI 11-03 Page 7 vii. Regional Bicycle/Pedestrian Coordinator,

viii. Regional Landscape Architect/Environmental Services Manager, ix. Construction Supervisor

Note - If the project is a permit project or Locally Administered Project the Regional Permit Engineer or Regional Local Project Manager, respectively, will initiate the Concept Meeting, using their discretion to invite the appropriate individuals. The project sponsor (municipality, developer, etc.) and Regional staff ultimately reviewing the project should be invited to the meeting.

b. At the meeting, the designer will provide a brief overview of the project and discuss the Concept Development items with the group. Based on the general consensus of the group, the intersection options to progress further will be identified.

c. The designer will prepare and distribute Concept Meeting Minutes to those involved in the Concept Meeting for review. The designer will ensure those who review the minutes agree with their content prior to finalizing.

d. If a roundabout remains feasible, continue to step 5. e. If all roundabout options are dismissed, the designer will document the

reasoning to an appropriate level of detail in the Concept Meeting Minutes and also include the reasoning for dismissal in the Design Approval Document. The designer will progress the remaining non-roundabout options per HDM Section 5.9 and abandon this process.

5. Geometric Design

The designer will: a. Develop the following design information for each roundabout option

being progressed, in accordance with the Department’s latest roundabout design guidelines and NCHRP report 672, Roundabouts: An Informational Guide – Second Edition:

i. Roundabout geometric data, including: 1. Complete the Critical Roundabout Design Parameters

Table (in Appendix B) for each roundabout option. An electronic version of this table can be found at: O:\Design\Design Resource\Info\Roundabout Information\RDI 11-03_roundabout design parameters.xls

2. Prepare detailed drawings showing the fastest path for each movement.

3. Complete the Fastest Path Table (in Appendix C) for each roundabout option. An electronic version of this table can be found at: O:\Design\Design Resource\Info\Roundabout Information\RDI 11-03_roundabout fastest paths.xls

4. Identify and document the design vehicle and frequency for each movement.

5. Draw AutoTrack vehicle paths for the design vehicle(s). ii. Summarize the design decisions by documenting any deviation(s)

from standard/desired roundabout design parameters included in Section 5.a.i above. It is preferred that this be accomplished in memo format (addressed to: “File” or, for consultant designed projects, the NYSDOT project manger) with a narrative and a table

http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_672.pdfhttp://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_672.pdf

RDI 11-03 Page 8 of non-conforming features. The table should include columns for: 1) element, 2) leg, 3) standard, 4) proposed and 5) justification & mitigation.

iii. Pavement Markings – Conceptual plans should be developed to a level of detail to identify lane assignments and vehicle paths.

iv. Landscaping – The designer should consider whether the use of strategically located landscaping might be advantageous as a means to reduce approach/entry speeds by limiting motorist’s visibility. For more information, see Chapter 9 in the NCHRP Report 672, Roundabouts: An Informational Guide – Second Edition.

v. Constructability – The designer should ensure there is a construction sequence that would allow each roundabout option to be constructed by having preliminary discussions with the Regional Traffic & Safety Office and the Construction Supervisor assigned to the project. A more detailed conversation will occur at the Mid-Design Review Meeting (see RDI 06-03, or subsequent issuance) for the preferred intersection option.

vi. Workshop meeting – At the designer’s discretion, a small-scale workshop meeting could be held to discuss the details of the above geometric information for the roundabout option(s) being considered. If this meeting occurs, it is recommended that the following attend:

1. Regional Traffic Engineer, 2. Design Supervisor, 3. Regional Roundabout Coordinator, 4. Main Office Intersection Design Squad Representative

Any comments offered at the Workshop should be incorporated into the design prior to step 6.

b. Develop conceptual plans for each traditional (stop and/or signal controlled) intersection option being progressed. Conceptual pavement marking plans should be developed to a level of detail to identify lane assignments and vehicle paths. Designers may wish to use RDI 10-04, or subsequent issuance, titled “Minor Intersection Design”, as a guide for the types of things to include/consider on the drawings.

c. Continue to step 6.

6. Geometric Meeting a. The designer will hold a Geometric Meeting with the following suggested

attendees: i. Regional Design Engineer,

ii. Regional Traffic Engineer, iii. Resident Engineer, iv. Design Supervisor, v. Regional Roundabout Coordinator,

vi. Main Office Intersection Design Squad Representative, vii. Regional Bicycle/Pedestrian Coordinator,

viii. Regional Landscape Architect/Environmental Services Manager, ix. Construction Supervisor

http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_672.pdfhttp://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_672.pdfhttps://www.dot.ny.gov/regional-offices/region1/repository/RDI%2006-03.Mid-Design%20Reviews.pdfhttps://www.dot.ny.gov/regional-offices/region1/repository/RDI_10-04_Minor_Intersection_Design.pdf

RDI 11-03 Page 9 Note - If the project is a permit project or Locally Administered Project the Regional Permit Engineer or Regional Local Project Manager, respectively, will initiate the Geometric Meeting, using their discretion to invite the appropriate individuals. The project sponsor (municipality, developer, etc.) and Regional staff ultimately reviewing the project should be invited to the meeting.

b. The designer will circulate the design information developed in step 5 to the Geometric Meeting attendees at least a couple working days in advance of meeting.

c. At the meeting, the designer will discuss the Geometric Design items with the group. The designer will seek general consensus on the details and decide which intersection options to move forward with.

d. The designer will prepare and distribute Geometric Design Meeting Minutes to those involved in the Geometric Design Meeting for review. The designer will ensure those who review the minutes agree with their content prior to finalizing.

e. If a roundabout remains feasible, continue to step 7. f. If all roundabout options are dismissed, the designer will document the

reasoning to an appropriate level of detail in the Geometric Meeting Minutes and include in Design Approval Document. The designer will progress the remaining non-roundabout options per HDM Section 5.9.

7. Geometric Alterations

If necessary, the designer will: a. Make any changes to the remaining intersection option(s) based on input

received at the Geometric Meeting. b. In rare instances, hold follow-up Geometric Alteration Meeting(s) until

general consensus is reached on the preliminary design. c. Prepare and distribute Geometric Alteration Meeting Minutes to those

involved in the Geometric Alteration Design Meeting. The designer will ensure those who review the minutes agree with their content prior to finalizing.

8. Complete Preliminary Design in accordance with NYSDOT and Region 1

policies/guidance. To document the decision making process and the selection of the chosen alternative, include the Concept, Geometric and Geometric Alterations information (as applicable) from steps 3 through 7 as a dedicated appendix in the Design Approval Document.

9. Initiate Final Design, including 3D modeling (if appropriate) for the project.

Public Involvement

As with any major project, public involvement is critical to its success. The public involvement process for roundabout intersections will be left up to the discretion of the design team, following appropriate NYSDOT and Region One guidance. It is recommended that the design team meet with the locally elected officials prior to any substantial design work being completed. Designers should refer to RDI 08-10, or subsequent issuance, for additional information and contact the Regional Design Community Participation Coordinator.

https://www.dot.ny.gov/regional-offices/region1/repository/RDI_08-10_Public_Involvement.pdf

RDI 11-03 Page 10 Lighting

For NYSDOT projects on the state highway system, the designer will follow the guidance in RDI 08-08, or subsequent issuance. If a roundabout will be constructed on a state highway, by means of a Highway Work Permit or Locally Administered Project, the designer shall follow the guidance in RDI 08-08, or subsequent issuance, with the following exceptions and/or additions:

• The lighting system shall be designed to the satisfaction of NYSDOT but purchased and installed by the permitee or municipality, as applicable.

• NYSDOT will take over maintenance and electrical costs for lighting upon completion of construction if NYSDOT has maintenance jurisdiction of the roundabout. If another entity (county, municipality, city, village, etc.) is responsible for the maintenance of the roundabout, that entity should also be responsible for maintenance and electrical costs associated with the lighting system.

References Document File Location \ Name

NCHRP Report 672 O:\Design\Design Resource\Info\Roundabout Information\NCHRP Report 672 - Roundabouts An Informational Guide 2nd Edition.pdf

Roundabout Design Parameters O:\Design\Design Resource\Info\Roundabout Information\RDI 11-03_roundabout design parameters.xls

Fastest Path Calculations O:\Design\Design Resource\Info\Roundabout Information\RDI 11-03_roundabout fastest paths.xls Keywords Intersection Design, Roundabout

https://www.dot.ny.gov/regional-offices/region1/repository/RDI_08-08v2_Highway_Lighting.pdfhttps://www.dot.ny.gov/regional-offices/region1/repository/RDI_08-08v2_Highway_Lighting.pdf

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APPENDIX A

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APPENDIX B

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APPENDIX C

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Purpose