Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Chapter 10/Construction and Maintenance Page 10-1 Roundabouts: An Informational Guide CHAPTER 10 CONSTRUCTION AND MAINTENANCE CONTENTS 10.1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-3 10.2 PUBLIC EDUCATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-3 10.3 CONSTRUCTION STAGING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-4 10.3.1 Construction under No Traffic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-4 10.3.2 Construction with Some Traffic Diverted . . . . . . . . . . . . . . . . . . . . 10-5 10.3.3 Construction under Full Traffic . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-8 10.4 WORK ZONE TRAFFIC CONTROL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-10 10.4.1 Pavement Markings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-10 10.4.2 Signing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-11 10.4.3 Lighting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-11 10.5 CONSTRUCTION PLANS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-11 10.6 CONSTRUCTION COORDINATION . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-11 10.6.1 Contractor and Designer Coordination . . . . . . . . . . . . . . . . . . . . . 10-12 10.6.2 Utility Coordination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-12 10.7 MAINTENANCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-13 10.7.1 Landscaping Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-13 10.7.2 Snow Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-13 10.7.3 Pavement Maintenance and Rehabilitation . . . . . . . . . . . . . . . . . 10-15 10.8 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-16
Roundabouts: An Informational Guide Page 10-2 Chapter 10/Construction and Maintenance LIST OF EXHIBITS Exhibit 10-1 Example of Roundabout Informational Brochure . . . . . . . . . . . . . 10-3 Exhibit 10-2 Example of Public Meeting Presentation Boards . . . . . . . . . . . . . . 10-4 Exhibit 10-3 Example of Construction under Partial Traffic . . . . . . . . . . . . . . . . 10-6 Exhibit 10-4 Examples of Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-8 Exhibit 10-5 Temporary Traffic Control During Roundabout Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-10 Exhibit 10-6 Maintenance Vehicle Parking Pullout within the Central Island . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-13 Exhibit 10-7 Example of Roundabout Plowed for Snow . . . . . . . . . . . . . . . . . . 10-14 Exhibit 10-8 Snow Accumulation in the Splitter Island . . . . . . . . . . . . . . . . . . . 10-15 Exhibit 10-9 Example Maintenance Project Staging Plan . . . . . . . . . . . . . . . . . 10-15
Chapter 10/Construction and Maintenance Page 10-3 Roundabouts: An Informational Guide 10.1 INTRODUCTION This chapter focuses on issues related to the actual construction of a round- about as well as issues related to ongoing maintenance. 10.2 PUBLIC EDUCATION One of the most important aspects of planning a roundabout construction project is providing public education. The public needs to be notified and educated whenever there is a change in traffic patterns. It can be especially important for a roundabout because the first roundabout in a city or region will be new to many motorists. The public involvement techniques discussed in Chapter 3 can be applied during the construction period. The following are some suggestions to help alleviate initial driver confusion: ⢠Hold public meetings prior to construction. ⢠Prepare news releases/handouts detailing what the motorist can expect before, during, and after construction. ⢠Install variable message signs before and during construction. ⢠Use travelers advisory radio immediately prior to and during construc- tion to disseminate construction information and driving instructions. ⢠Use websites or other online social media to disseminate information on construction progress and on use of the roundabout. ⢠Install signing during and after construction warning of changed traffic patterns. Exhibit 10-1 illustrates a roundabout brochure that was developed for the installation of a new multilane roundabout in Clackamas County, Oregon. This provides general information about roundabouts and provides all users instruc- tions for navigating the new roundabout in their community. Public education during con- struction is as important as the public education effort during the planning process. Clackamas County, Oregon Exhibit 10-1 Example of Roundabout Informational Brochure
Roundabouts: An Informational Guide Page 10-4 Chapter 10/Construction and Maintenance As part of the new roundabout installation in Clackamas County, a public information meeting was also held. Exhibit 10-2 provides two of the presentation boards that were used at the meeting to illustrate the proposed roundabout plan and expected project schedule. Exhibit 10-2 Example of Public Meeting Presentation Boards Additional public education information and specific project examples are provided in Chapter 3. 10.3 CONSTRUCTION STAGING Roundabouts can be constructed under three types of traffic conditions: ⢠With all traffic diverted away from the work area, ⢠With some traffic diverted, or ⢠Under full traffic. The guiding principle is to minimize staging and to provide large sections of the project to construct during each construction stage. This will increase quality of construction, reduce driver confusion, reduce the construction time, and save construction costs. Generally, diverting or detouring as much traffic from the intersection as possible is the most desirable option. However, it is recognized that in many circumstances full (or even partial) detours are not feasible. 10.3.1 CONSTRUCTION UNDER NO TRAFFIC It is highly desirable to construct a roundabout without traffic passing through the work zone. This will significantly reduce the construction time and cost and will increase the safety of the construction personnel. This is possible under two common scenarios: the roundabout is on a new roadway, or all traffic can be diverted away from the roundabout (even for a short period of time). Construction staging should be considered during the prelimi- nary design of the roundabout, especially if it must be built under traffic.
Chapter 10/Construction and Maintenance Page 10-5 Roundabouts: An Informational Guide Anecdotal experience suggests that minimizing detour changes during con- struction is desirable to reduce public confusion through the time of construction. It is easier to communicate one or two different detours to the driving public through the course of a project versus constantly changing routes. Prior to detour- ing traffic, peripheral items (e.g., signing, illumination, and landscaping) outside the traveled way or with minimal effect on traffic can be completed to reduce the time the road is closed and the detour is in place. 10.3.2 CONSTRUCTION WITH SOME TRAFFIC DIVERTED In some cases, if it is not possible to detour all of the traffic from the intersec- tion, certain approaches may need to remain open to traffic. Construction under partial traffic commonly includes closing the minor roadway approaches, with the major street movements maintained either on the existing roadway or on tempo- rary roadways implemented as part of the construction staging. The primary purpose of this technique is to eliminate intersection conflicts while still allowing some traffic to use the intersection. Exhibit 10-3 provides a case study that illustrates an example of roundabout construction under partial traffic (1). The case study discusses construction staging at the Baldwin Road/Coats Road/Indianwood Road intersection in Oakland County, Michigan, where a single-lane roundabout was installed while maintaining traffic flow on the major roadway (Baldwin Road) through the use of temporary roadways. The majority of the roundabout construction occurred during Stage 2 due to the ability to close the minor approaches (Coats Road and Indianwood Road). Otherwise, the roundabout construction would have required additional staging, more complex traffic control, and an extended construction timeline.
Roundabouts: An Informational Guide Page 10-6 Chapter 10/Construction and Maintenance Exhibit 10-3 Example of Construction under Partial Traffic Baldwin Road/Coats Road/Indianwood Road A single-lane roundabout was constructed at the intersection under partial traffic using four construction stages. Baldwin Road is the major roadway, which includes the west and south approaches of the intersection. The shaded portions of the plans represent the permanent pavement under construction, temporary pavement being placed for construction staging, or temporary pavement under traffic. Stage I: Temporary Roadway Construction Construct a 12-ft (3.6-m) temporary roadway adjacent to the existing Baldwin Road for the east and south approaches of the intersection. Construct replacement culvert over the south approach. Maintain two-way traffic on the east, west, and north approaches. Maintain traffic on the south approach with partial lane closure controlled with flagging. Stage II: Primary Roundabout Construction Close Coats Road and Indianwood Road to traffic. Shift traffic to temporary roadway on east and west approaches to maintain two-way traffic on Baldwin Road. Close southeast business driveway and restrict northwest business driveway to right-in/right-out only. Construct all roundabout improvements on the east and north approaches. Construct partial roundabout improvements on west and south approaches. Construct temporary pavement at the west and south approaches.
Chapter 10/Construction and Maintenance Page 10-7 Roundabouts: An Informational Guide Exhibit 10-3 (cont.) Example of Construction under Partial TrafficStage III: West Approach Construction Complete roundabout improvements on west approach. Remove temporary pavement on south and west approaches. Shift traffic to temporary roadways on west approach to maintain two-way traffic on Baldwin Road. Close northwest business driveway and open southeast business driveway to right-in/right-out only movements. Install permanent signing on the north and east approaches and on the central island. Install signing and markings on the south and west approaches. Open Coats Road and Indianwood Road to traffic on permanent roadways. East, north, and south approaches operate as roundabout with two-way traffic. Stage IV: South Approach Construction Shift traffic to permanent roadway on west approach. Shift traffic to temporary roadway on south approach. Complete improvements on the south approach, including splitter island, completion of permanent roadway on the west side of the approach and removing temporary pavement. Complete improvements on the west approach, including splitter island and removing temporary pavement. Install remaining permanent signing and striping on all approaches.
Roundabouts: An Informational Guide Page 10-8 Chapter 10/Construction and Maintenance 10.3.3 CONSTRUCTION UNDER FULL TRAFFIC If it is not possible to detour all approaches, detour as many approaches as possible. This reduces the volume of traffic through the intersection and the num- ber of turning movements available. However, when under full traffic, there are typically some intersection conflicts that should be carefully monitored and exe- cuted with the appropriate type of traffic control. One possible sequence for staging construction under full traffic is as follows: 1. Install signing and lighting. (Signing should be initially covered.) 2. Construct outside widening if applicable. 3. Reconstruct or resurface approaches if applicable. 4. Construct splitter islands and delineate the central island. At this point the signs should be uncovered, and the intersection should operate as a roundabout. A recently completed splitter island is shown in Exhibit 10-4(a). 5. Finish construction of the central island. 6. Prepare final grade and apply final paving course for the circulating road- way and entry/exits. Grading of the circulatory roadway is shown in Exhibit 10-4(b). Exhibit 10-4 Examples of Construction (a) Splitter island construction (Portland, Oregon)
Chapter 10/Construction and Maintenance Page 10-9 Roundabouts: An Informational Guide Prior to the work that would change the traffic patterns to that of a roundabout, certain peripheral items may be completed. This would include permanent signing (covered), lighting, and some pavement markings. These items, if installed prior to the construction of the central island and splitter islands, would expedite the opening of the roundabout and provide additional safety during construction. When work has commenced on the installation of the roundabout, it is desirable that it be completed as soon as possible to minimize the time the public is faced with an unfinished layout or where the traffic priority may not be obvious. If possible, all work, including the installation of splitter islands and striping, should be done before the roundabout is open to traffic. If it is necessary to leave a roundabout in an uncompleted state overnight, the splitter islands should be constructed before the central island. Any portion of the roundabout that is not completed should be marked, delineated, and signed in such a way as to clearly outline the intended travel path. Pavement markings that do not conform to the intended travel path should be removed. Other staging considerations are as follows: ⢠If projects must be constructed under traffic, night work is an option to reduce the impacts to traffic during peak hours. ⢠Flagging can be used on the approaches and exits to allow the contractors to work. ⢠Temporary signals can be used on the approaches under certain stages, if applicable. ⢠Temporary roadway construction may be necessary during certain stages of construction. ⢠The use of a temporary traffic pattern that is counter to normal roundabout operation (i.e., vehicles circulating clockwise instead of counterclockwise) is undesirable. Exhibit 10-4 (cont.) Examples of Construction (b) Circulatory roadway sub-grade construction (Portland, Oregon)
Roundabouts: An Informational Guide Page 10-10 Chapter 10/Construction and Maintenance Phasing should (to the extent possible) be aimed to train drivers in correct driving rules and habits once fully opened. This includes operating the inter- section in a similar pattern to the final roundabout configuration. Exhibit 10-5 illustrates the use of cones and barrels to delineate the roundabout approaches and circulatory roadway while physical construction of the splitter island and central island is occurring. Exhibit 10-5 Temporary Traffic Control During Roundabout Construction Towson, Maryland 10.4 WORK ZONE TRAFFIC CONTROL As is the case with any construction project, before any work can begin, all traffic control devices should be installed as indicated in the traffic control plan or recommended typical details. This traffic control should remain in place as long as it applies and then be removed when the message no longer applies to the condition. During the construction of a roundabout it is essential that the intended travel path be clearly identified. This may be accomplished through pavement markings, signing, delineation, channelizing devices, and guidance from police and/or construction personnel, depending on the size and complexity of the roundabout. Care should be taken to minimize the channelizing devices so that motorists, bicyclists, and pedestrians have a clear indication of the required travel path. Each installation should be evaluated separately; a definitive guideline for the installation of roundabouts is beyond the scope of this guide. Refer to Part 6 of the MUTCD for requirements regarding work zone traffic control (2). 10.4.1 PAVEMENT MARKINGS The pavement markings used in work zones should be the same layout and dimension as those used for the final installation. Because of the confusion of a work area and the change in traffic patterns, additional pavement markings may be used to clearly show the intended direction of travel. In some cases when pave-
Chapter 10/Construction and Maintenance Page 10-11 Roundabouts: An Informational Guide ment markings cannot be placed, channelizing devices (i.e., cones, tubular markers, and/or drums) should be used to establish the travel path. 10.4.2 SIGNING The signing in work zones should consist of all necessary signing for the effi- cient movement of traffic through the work area, pre-construction signing advising the public of the planned construction, and any regulatory and warning signs neces- sary for the movement of traffic outside of the immediate work area. The permanent roundabout signing should be installed where practical during the first construction stage so that it is available when the roundabout is operable. Permanent signing that cannot be installed initially should be placed on temporary supports in the proposed location until permanent installation can be completed. 10.4.3 LIGHTING Temporary or permanent lighting, as described in Chapter 8, should be used to light the work area. A newly constructed or incomplete roundabout at night can be a surprise to drivers unless it is clearly visible when approaching the inter- section. It is particularly important to provide lighting in construction areas for pedestrians and bicycles to ensure that drivers are aware of their presence and provide guidance for all users to navigate the intersection. 10.5 CONSTRUCTION PLANS The requirements of every agency are different when it comes to construction plans and documents. However, plan sheets specifically important to roundabout construction are: ⢠Staging plan with detour routes (as appropriate), ⢠Staking plan with curve data (coordinates, radius), ⢠Paving plan and jointing plan (concrete pavement), ⢠Lighting plan, ⢠Signing plan, and ⢠Pavement marking plan. Example construction plans can be found in the Kansas Department of Transportationâs Kansas Roundabout Guide (3) and the Wisconsin Department of Transportation Facilities Development Manual (4). 10.6 CONSTRUCTION COORDINATION As with all types of roadway construction projects, construction of a round- about requires close coordination during the planning and implementation stages. The designer should remain engaged in the project through construction to ensure
Roundabouts: An Informational Guide Page 10-12 Chapter 10/Construction and Maintenance that design details are properly executed and respond to contractor questions. The design and construction team should also coordinate closely with utilities to ensure that the existing equipment can be preserved, as needed, and new equip- ment can be integrated into the system. The following sections provide additional details regarding some of the coordination that should be considered during construction of a roundabout. 10.6.1 CONTRACTOR AND DESIGNER COORDINATION Once a roundabout goes to construction it is important that any changes from the plan be discussed with the designer. Changes in lane widths, radii, grades, or other geometric parameters can affect safety and operational perfor- mance by impacting vehicle speeds, vehicle alignments, accommodation of trucks, and so forth. For multilane roundabouts, it is particularly important that the engineer be notified and be on site to ensure that the contractor precisely lays the markings according to the plan. If the markings stray from the design, the roundabout may not operate as expected because the entering and receiving lanes need to line up appropriately and spiral markings should flow naturally. Similarly, where con- crete pavement is used, the joint plans are an important design feature that must be carefully implemented by the contractor. Joint lines can be mistaken for lane lines and therefore it is important that additional joints or changes to the joint patterns be reviewed by the engineer. Engineers should ensure that the contractor has a clear understanding of the design details for the truck apron. Contractors may build the truck apron flush to the circulatory roadway (which may lead to higher vehicle speeds) or may leave too much exposure on the face of the truck apron curb (which would discourage use by trucks or lead to truck load shifting). In either case, the accurate construc- tion of the truck apron is important to achieving the intended intersection operations. 10.6.2 UTILITY COORDINATION All roundabout construction should be closely coordinated with the local util- ity company. Existing utilities should be identified during the initial design stages of the roundabout to identify potential conflicts with utilities. This can be achieved through conducting a detailed field survey, reviewing existing intersection record drawings (as-built plans or as-constructed plans), and obtaining information from the utility company. If the roundabout construction will affect existing facilities, the utility company should be notified and integrated into the construction planning process to ensure proper relocation. Installation of new equipment at the roundabout, such as illumination, conduit for future potential signalization, and drainage facilities should also be coordinated with the utility company to ensure that the new facilities can be adequately integrated into the existing system. Manhole placement should be included in the utility coordination. While the placement is specific to each site and may be dictated by the existing system, manholes should be located to allow
Chapter 10/Construction and Maintenance Page 10-13 Roundabouts: An Informational Guide for safe access by maintenance crews and only minimal disruption to traffic at the roundabout. 10.7 MAINTENANCE Maintenance of roundabouts is similar to that of any other intersection. A plan is necessary to carry out the maintenance operation, be it trimming the shrubs, snow removal, or routine pavement maintenance. 10.7.1 LANDSCAPING MAINTENANCE As discussed in Chapter 9, choosing landscaping objects that require only periodic maintenance is preferred, particularly within the central island and split- ter islands. One option for improving maintenance access to the central island is to provide an inset for a maintenance vehicle, as illustrated in Exhibit 10-6. This option is not necessary for most roundabouts, but may be desirable where more regular maintenance is required or where high traffic volumes may make it diffi- cult or unsafe to access the central island. Exhibit 10-6 Maintenance Vehicle Parking Pullout within the Central Island Bend, Oregon 10.7.2 SNOW REMOVAL Each agency in cold climates has its own technique and routine for plowing snow. For the first roundabout in a jurisdiction, it may be helpful to develop a plowing sequence plan until the plow operators become familiar and more effi- cient with plowing the roundabouts. Many jurisdictions have standard widths for snowplows within their fleet. In areas where snow removal is anticipated to be a regular occurrence, the geometric design of the roundabout may need to be tailored to accommodate the width of the plow blade. Some maintenance crews have noted that roundabouts make it easier to turn around snowplows as well. Exhibit 10-7 shows an example of a roundabout plowed for snow.
Roundabouts: An Informational Guide Page 10-14 Chapter 10/Construction and Maintenance One common method for snow removal is for the snowplow to start on the innermost section of the circulatory roadway, often on the truck apron, and keep circulating while spiraling outward with each revolution clearing the snow from the circulatory roadway. At the same time, a second plow operator will clear the entries and exits, or the same plow operator will clear the approaches once the circulatory roadway is clear. The crown of the circulating roadway, if present, will also help dictate the plowing sequence of a roundabout. One of the biggest pitfalls with plowing snow from the roundabout is identi- fying the location of the raised truck apron and other curb locations after heavy snowfall has occurred. Damage to the apron or to the curbs may occur if care is not taken by the operator in identifying the curb locations. Snow storage should also be considered when plowing at a roundabout. Storage should not create a sight obstruction for drivers approaching or circulating the roundabout and should not affect pedestrian access through a roundabout. Exhibit 10-8 illustrates the limited sight-distance that can occur due to snow accu- mulation along the outside edge of the roundabout. Knocking down the height of the snow piles or removing snow from the islands may be necessary after pro- longed periods of snowfall. It is also important that snow not be stored such that it will thaw and then freeze as ice on the circulatory roadway. Snow plowed from the roadway may contain road salts and other automobile waste that could impact vegetation if placed in sensitive landscaped areas. Exhibit 10-7 Example of Roundabout Plowed for Snow Cle Elum, Washington
Chapter 10/Construction and Maintenance Page 10-15 Roundabouts: An Informational Guide 10.7.3 PAVEMENT MAINTENANCE AND REHABILITATION Pavement maintenance and rehabilitation projects are similar to new con- struction as far as construction staging. It is preferred that maintenance be conducted under as little traffic as possible; however, it can be done under traffic using the techniques described earlier in this chapter. Exhibit 10-9 provides an example of flagging operation for conducting maintenance work on one quadrant of an existing roundabout. The work was completed under full traffic with four flaggers (one at each approach) to guide traffic flow. In addition, it may be neces- sary to include another flagger on the central island to assist with movement through the roundabout. Exhibit 10-8 Snow Accumulation in the Splitter Island View looking left from the entry (New York) Exhibit 10-9 Example Maintenance Project Staging Plan Source: Washington State Department of Transportation (5)
Roundabouts: An Informational Guide Page 10-16 Chapter 10/Construction and Maintenance 10.8 REFERENCES 1. Orchard Hiltz & McCliment, Inc., and Hampton Engineering Associates, Inc. âStaging Construction.â Construction plans for Baldwin/Indianwood/Coats Road Roundabout, Oakland County, Michigan, 2003. 2. Manual on Uniform Traffic Control Devices. FHWA, Washington, D.C., 2003. 3. Kittelson & Associates, Inc., and TranSystems Corporation. Kansas Roundabout Guide: A Supplement to FHWAâs Roundabouts: An Informational Guide. Kansas Department of Transportation, Topeka, Kansas, 2003. 4. Wisconsin Department of Transportation. Facilities Development Manual. http://roadwaystandards.dot.wi.gov/standards/fdm/Forms/11-26-050p01.pdf. Accessed March 2010. 5. Washington State Department of Transportation. Work Zone Traffic Control Plans. www.wsdot.wa.gov/Design/Standards/PlanSheet/WZ-1.htm. Accessed August 2009.
