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Although roundabouts have recently gained popularity and use in the United States, minimal guidance is available for constructing roundabouts or installing, maintaining, and removing temporary traffic control devices in work zones where roundabouts are constructed. This document provides considerations and typical applications to assist field staff in setting up temporary traffic control for both new construction and maintenance activities.
The information contained in this document has been compiled from a number of source documents from State agencies and research organizations including: Virginia (1), Oregon (2), Washington (3), and Wisconsin (4) as well as the Transportation Research Board (5).
Roundabouts located at Interstate 70 and Edwards Access Road in Edwards, CO (Photo courtesy of Felsburg Holt & Ullevig; photography: Terry Shapiro)
(Photo courtesy of NCDOT)
The one-way flow operational characteristics and roadway geometry of roundabouts make them different from most other intersections negotiated by drivers. Temporary traffic control during maintenance and construction activities must provide clear guidance to drivers, who in some cases are unfamiliar with roundabout operations.
The traffic control guidelines outlined in this document can be used during various maintenance and construction activities such as pavement repair, striping, signing, delineation, landscaping, and intersection repair as well as during the construction of new roundabouts. The Manual on Uniform Traffic Control Devices (MUTCD) (6), as well as State and local standards for guidance should be applied in reference to sign spacing, taper lengths, use of shadow vehicles (i.e., a vehicle used to protect workers from impact from errant vehicles) and other general temporary traffic control provisions.
Each intersection, adjacent road network, set of user needs and project construction method is unique. Temporary traffic control plans should reflect the diversity of considerations at intersections where roundabout construction and maintenance operations take place.
Roundabouts can be constructed under three types of traffic conditions (5. pp. 10-4):
Generally, diverting or detouring traffic away from the intersection is most desirable (5, pp. 10-4). However, this may not always be possible, in such cases; strategies to manage traffic operating through the work zone must be developed.
During the construction of a new roundabout, closures and detours should be used at the intersection when possible. By diverting traffic to other roadways, recognizable benefits include:
However, re-routing traffic creates concerns of its own, such as:
The benefits and concerns should be discussed with stakeholders such as public works departments, emergency responders, businesses, and adjacent property owners when deciding what traffic detour options to consider.
In cases where it is not possible to detour all the traffic, certain intersection approaches may need to be strategically kept open to traffic during construction. For example, minor roadway approaches may be closed and major street traffic maintained on the existing roadway or a temporary roadway built as part of construction staging (5, pp. 10-5). Other considerations for this hybrid approach may include:
A project in Winnebago County, Wisconsin involved shifting traffic on Route 45 to the east and west sides of the roundabout construction at Lake Buttes Des Morts Drive during successive phases. While the east approach of Lake Buttes Des Morts Drive was closed to traffic, the motorists on Route 45 were shifted to the west through the intersection. In the next phase of construction, the west supplementary approach was closed and Route 45 traffic was moved to the east. The intersection was open to Route 45 traffic at all times. Appendix A includes construction staging and traffic control plans.
In Gilbert's Corner, VA, four new roundabouts were to be constructed - one at Gilbert's Corner (intersection of Route 50 and Route 15), one at the intersection of Route 50 and Watson Road, one at the intersection of Route 50 and a new connector road, and one at the intersection of Route 15 and a new connector road. Roundabouts along Routes 15 and 50 were constructed first. During Phase 1 construction of the roundabout at the intersection of Routes 15/50, westbound traffic continued along Route 50 while construction of the southern half of the roundabout took place. In Phase 2, Route 50 traffic was diverted via a connector road to Route 15 while construction of the northern half of the roundabout took place. Construction staging and traffic control plans are included in Appendix B.
Prior to commencing work that would change traffic patterns, installation of certain peripheral items could expedite the opening of the roundabout and provide additional safety during construction (5, pp. 10-9). This could include permanent signing, lighting, and pavement markings. Once work commences, it is desirable for it to be completed as soon as possible to minimize time when the public is faced with an unfinished layout, or where traffic patterns may not be obvious (5, pp 10-9).
The following list presents a possible sequence for staging construction under full traffic constructions:
" install lighting. " install and cover the permanent roundabout signing until construction of splitter islands and central island. Traffic is expected to follow the new roundabout path upon commencement of central island installation, which requires proposed signing to be in place and uncovered. " construct outside widening, as needed. " reconstruct or resurface approaches, if needed. " construct splitter islands first, and delineate the central island. At this time, it is necessary to uncover permanent signing and operate the intersection as a roundabout. " complete the central island. " prepare final grade and apply paving course for the circulating roadway and entry/exit.
(Photo from Virginia DOT website)
(Photo courtesy of WSDOT)
An example of construction under full traffic occurred at the Raymond Avenue and Collegeview Avenue roundabout in the Town of Poughkeepsie, Dutchess County, NY. During Phase I, a temporary right turn lane was constructed on the eastbound approach to Collegeview Avenue while the western portion of the roundabout underwent construction. In Phase II, temporary roadways were constructed on the northbound and westbound approaches to Raymond Avenue as crews constructed the eastern portion of the roundabout. Construction staging and traffic control plans are shown in Appendix C.
Pavement repair, striping operations, maintenance of the truck apron, repairs to a splitter island, as well as other activities can require the establishment of a work zone within a roundabout. Appendix D contains four example temporary traffic control plan applications for roundabouts:
" Typical Application 1a, 1b, 1c - Single-Lane Roundabouts: Partial Closure; " Typical Application 2 - Single-Lane Roundabouts: Partial Closure with Detour; " Typical Application 3 - Multi-Lane Roundabouts: Inside Lane Closure; " Typical Application 4 - Multi-Lane Roundabouts: Outside Lane Closure.
Typical Applications 1a, 1b, and 1c illustrate how traffic control may be established when one quadrant of the roundabout is closed to traffic. The examples show how reverse flow through the roundabout may occur with use of flagging operations. Typical Application 2 demonstrates the use of a detour in lieu of reversing the flow through the roundabout when one quadrant is closed to traffic. Typical Application 3 shows how to set up temporary traffic control when work is being performed on the inside lane of a multi-lane roundabout. On a multi-lane approach, a lane drop is used to divert traffic to the inside lane before entering the roundabout. Typical Application 4 illustrates the temporary traffic control needed to perform work within a quadrant of a multi-lane roundabout. In this case, the inside lane is closed throughout the entire roundabout and the outside lane is closed in one quadrant. Traffic is diverted to a single lane before entering the roundabout and reverse flow is used under flagging operations.
These applications can be modified for more than four approaches by replicating each additional approach to reflect similar signing and channelization device spacing, as well as by designing taper and buffer lengths and sight distance spacing to conform to the MUTCD (6) and State or local standards.
Each roundabout is unique and the traffic control must be developed that considers the conditions and location of the temporary work zone operations. A detour could better serve traffic by minimizing delay and increasing safety and should always be considered where appropriate. For work within the existing roundabout but outside of the driving lane, such as work on a shoulder or within the truck apron or island, flagging operations may not be needed. A single ROAD WORK AHEAD sign per approach may be used in lieu of a more robust temporary traffic control package. Reference to the MUTCD (6), State or local guidelines may be necessary to adhere to other relevant traffic control applications.
When leaving the roundabout in an uncompleted state overnight, it is important to construct the splitter islands before constructing the central island. The splitter islands help to delineate opposing flow and guide motorists to enter the roundabout in counterclockwise fashion. Temporary traffic signals may also be an option, depending on construction staging, open approaches, available paths, and work occurring within the intersection.
Other Considerations (5, pp. 10-9):
In many cases, a flagging operation is required as a means of controlling traffic in a roundabout work zone scenario. Considerations for both single-lane and multi-lane roundabout applications include:
The use of a shadow vehicle (i.e., a vehicle used to protect workers from the impact of errant vehicles) is sometimes required for both single-lane and multi-lane applications, and could be considered for use in all applications, just as shadow vehicles are used for applications other than roundabouts. For more information, refer to the MUTCD, Roadside Design Guide and applicable State or local guidance.
Care should be taken to ensure that, at a minimum, existing pedestrian traffic is managed according to work zone and American's with Disabilities Act (ADA) standards for pedestrians set forth by the following references. If bicycle facilities exist at the roundabout, existing guidance for accessibility within work zones should be applied. Alternate routes for pedestrians and bicycles should be established if existing routes are temporarily interrupted. Alternate routes should be signed in advance and should be free of hazards and obstructions. For pedestrian and ADA legislation and guidance, refer to:
Consider providing brochures on how to drive, walk and bicycle through the roundabout. Consider the use of other public education tools such as public information meetings, press releases, project newsletters, portable changeable message signs, web site, and the news media. (4) The use of public information and education is encouraged when roundabouts are first introduced into a community or the roundabout is situated where a unique group of users are present. For example, if the roundabout is located near a school, senior housing, or tourist attraction, information could be provided that tailors a message to a specific group of users.
Information for these guidelines was adapted from:
This appendix contains construction staging and traffic control plans for a project in Winnebago County, Wisconsin that involved shifting traffic on Route 45 to the east and west sides of the roundabout construction at Lake Buttes Des Morts Drive during successive phases. While the east approach of Lake Buttes Des Morts Drive was closed to traffic, the motorists on Route 45 were shifted to the west through the intersection. In the next phase of construction, the west supplementary approach was closed and Route 45 traffic was moved to the east. The intersection was open to Route 45 traffic at all times. This example shows the construction of a roundabout where some traffic was diverted.
This appendix contains construction staging and traffic control plans for a new roundabout that was constructed in Gilbert's Corner, Virginia and is an example of where a roundabout was built with traffic detoured. The roundabout was constructed at the intersection of Route 50 and Route 15. During the first phase of roundabout construction (noted as Phase 3 in the plans), eastbound and westbound traffic continued along Route 50 while construction of the southern half of the roundabout took place. Also during this phase, traffic on Route 15 was detoured. In the second phase of roundabout construction at this intersection (noted as Phase 4 in the plans), Route 50 traffic was diverted via a connector road to Route 15 while construction of the eastern half of the roundabout took place. In the final phase of roundabout construction (noted as Phase 5 in the plans), the roundabout was opened to full traffic as the splitter islands and truck apron were completed.
This appendix contains construction staging and traffic control plans for the Raymond Avenue and Collegeview Avenue roundabout in the Town of Poughkeepsie, Dutchess County, NY and is an example of construction under full traffic. During Phase I, a temporary right turn lane was constructed on the eastbound approach to Collegeview Avenue while the western portion of the roundabout underwent construction. In Phase II, temporary roadways were constructed on the northbound and westbound approaches to Raymond Avenue as crews constructed the eastern portion of the roundabout.
Phase I Traffic Pattern Raymond Avenue and Collegeview Avenue Roundabout
Phase II Traffic Pattern Raymond Avenue and Collegeview Avenue Roundabout
This appendix contains examples of typical applications for how maintenance operations are performed within existing roundabouts. Each typical application details whether the application is for partial closure of a single- or multi-lane roundabout, and specifies which lane is closed. The typical applications give considerations for temporary traffic control use and originate from State practices, as indicated in each example.
Typical Application 1a
Single-Lane Roundabouts: Partial Closure
(Source: Virginia DOT (1). Work Area Protection Manual, 2011 Edition, Figure TTC-31.0)
Reference: (1, pp. 6H-70)
Typical Application 1b
Single-Lane Roundabouts: Partial Closure
(Source: Oregon DOT (2). Temporary Traffic Control Handbook for Operations of Three Days or Less, Diagram 640)
|Posted Speed||Spacing Between Signs||Buffer Speed|
Reference: (2, pp. 122)
Typical Application 1c
Single-Lane Roundabouts: Partial Closure
(Source: Washington DOT (3). Work Zone Traffic Control Guidelines, TCD 13)
Reference: (3, pp. 1-19)
Typical Application 2
Single-Lane Roundabouts: Partial Closure with Detour
(Source: Oregon DOT (2). 2011 Oregon Temporary Traffic Control Handbook for Operations of Three Days or Less)
Reference: (6, pp. 670,672)
Typical Application 3
Multi-Lane Roundabouts: Inside Lane Closure
(Source: Virginia DOT (1). Work Area Protection Manual, 2011 Edition, Figure TTC-32.0)
Reference: (1, pp. 6H-72)
Typical Application 4
Multi-Lane Roundabouts: Outside Lane Closure
(Source: Virginia DOT (1). Work Area Protection Manual, 2011 Edition, Figure TTC-33.0)
Reference: (1, pp. 6H-74)
The American Traffic Safety Services Association (ATSSA)
15 Riverside Parkway, Suite 100
Fredericksburg, VA 22406-1022
This material is based upon work supported by the Federal Highway Administration under grant agreement No. DTFH61-06-G-00004.
Any opinions, findings, and conclusions or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the Federal Highway Administration.