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76 APPENDIX D Case Examples California (Caltrans) Roundabout Selection â¢ Caltrans uses an Intersection Control Evaluation (ICE) policy for selecting intersection control â¢ The Caltrans ICE policy was published in 2013 and applies to all project types on intersections and interchanges on the State Highway System. â¢ The motivation for the ICE policy was originally systematic implementation of roundabouts and was expanded to refer to other intersection types. â¢ For the past 7 or 8 years the Caltrans Safety Management Program was promoting roundabouts as a countermeasure. â¢ Most (approximately 95%) of roundabouts on the ground in California are a result of local agency desire, action and funding, and occurred before the ICE was put in place. Modifications to Existing Roundabouts â¢ One state highway roundabout was originally constructed as a partial multilane roundabout was converted to a single- lane roundabout. â¢ In Long Beach, a redesign of a multilane roundabout/traffic circle hybrid is planned to reduce capacity but not reduce the diameter of the existing circle. The project will reduce the width of the roundabout approaches and circulatory roadway, and was motivated by a high number of property damage only crashes. While the modifications will increase vehicle delay, the expectation is to see a reduction in the number of crashes. Design Vehicle â¢ The design vehicle is dictated by the Surface Transportation Assistance Act (STAA). â¢ The design vehicle depends on which ânetworkâ the inter- section or interchange is on, and the classification of the road. â¢ Four STAA vehicle types are: STAA 53, STAA 48, STAA Double, STAA ELLN (Extralegal Load). â¢ This varies slightly from other state DOT nomenclature but the vehicles are similar sizes. â¢ The design vehicle accommodation is customized based on intersection traffic conditions. â¢ Some effort to accommodate extra sized loads. â¢ Three roundabout rodeos have been conducted, and all were highly successful. Accelerated, Low-Cost Roundabouts â¢ Caltrans is open to the learning more about opportunities but it seems to be something that may be more interesting to municipalities. â¢ Los Angeles completed an overnight implementation of a roundabout. â¢ City of Modesto implemented a temporary roundabout over the course of a few days using channelizers and markings that has been in service for seven years. Implementation and Effectiveness of Policies â¢ Since the ICE policy went into effect there has been a dramatic change in the number of roundabout alternatives being evaluated and selected, and a reduction in the time to determine if the roundabout is a viable alternative. â¢ The policy requires the consideration of roundabouts, which was inconsistent and infrequent prior to ICE. â¢ There are no examples of ICE where the optimum outcome was not a roundabout. â¢ In the ICE process, a well-conceived roundabout alternative is very competitive. Quality Control â¢ Review process within Caltrans is not formal. â¢ Case-by-case review. â¢ Help municipalities access the technical assistance through FHWA. â¢ Relying on consultant reviews through an informal process. â¢ Caltrans encouraging project managers to utilize peer review in the design contracts for more complex locations. Connecticut (ConnDOT) Roundabout Selection â¢ Most roundabout proposals are coming from municipalities but ConnDOT also proposes them. â¢ The request from municipality is usually made by the town engineer or public works director but just was just recently approached by a town planner. â¢ Most exposure to roundabouts in Connecticut came through word of mouth or engineering publications. â¢ Connecticut differs from other states because there is no county government, and the two major stakeholders are the state and the municipality. â¢ If there is strong support from the town it makes the process go quicker. â¢ Initial installation faced strong opposition; there were 300+ people at the public hearing, but strong political support to deliver the project. In the end, crashes were reduced and congestion went away, accomplishing the major goals of the project. â¢ ConnDOT is focused on installing roundabouts where they can be successful. Phased Implementation Approach â¢ ConnDOT is interested in a phased approach, but have not done so yet. â¢ The last roundabout that was built was designed for 20 years out and it was built with excess capacity. ConnDOT has seen that the roundabout could have been opened up as a single-lane roundabout. â¢ ConnDOT has six multilane roundabouts and three could open as single lane roundabouts for the first ten years,
77 eliminating the ability for drivers to cross over lanes and taking the fastest path through the roundabout. â¢ ConnDOT is starting to question the traffic volume projec- tions, and instead making the roundabout work for ten years. Modifications to Existing Roundabouts â¢ ConnDOT has not modified any roundabouts in Connecticut. â¢ ConnDOT has modified older rotaries. â¢ First rotary modification was in was in Killingworth, Connecticut. â¢ There was no deflection so ConnDOT installed a truck apron to improve safety. â¢ ConnDOT received a National Roadway Safety award from FHWA for the Killingworth rotary modification. â¢ A rotary in Seymour, Connecticut is being modified now for less than $700,000 as opposed to $2,000,000 for a new roundabout. â¢ Because of the reduced cost the Seymour project is getting a lot of support. Design Vehicle â¢ WB-50 used to be the default design vehicle, but now a WB-62 or WB-67 is most commonly used. â¢ WB 62 for most of the movements in the intersection and WB-67 for landscaping. â¢ Low clearance truck trailers (lowboys) have been chal- lenging. â¢ For lowboy accommodation ConnDOT keeps the same cross-slope for the circulatory roadway and truck apron. â¢ One roundabout has an 11% slope on the approach to the roundabout and there have been no issues with plowing. â¢ Splitter islands have a hole cast for installing a rod in the winter, which serves as a warning device to the alert the plow driver to the location of the splitter island. â¢ The center island truck apron must be at least as wide as the snow plow wheel base width. â¢ One concrete truck apron was chipped by a plow so ConnDOT now uses a granite curb detail with a chamfer. Accelerated, Low-Cost Roundabouts â¢ Because of rotary retrofits, this is not as applicable. â¢ Some towns are trying minis. In one case the center island was developed using only paint that hasnât been as effective. There could be some challenges with implementing Mini roundabouts in in Connecticut. â¢ ConnDOT is putting extra emphasis on making sure fastest paths are checked at mini-roundabouts. Implementation and Effectiveness of Policies â¢ ConnDOT was initially focused first on single-lane roundabouts but is now branching out toward multilane roundabouts. â¢ The highway design manual is currently being rewritten and will have additional guidance on roundabouts. â¢ ConnDOT is interested in putting in language specifying a preference for roundabouts. â¢ ConnDOT is not able to influence consultant design. â¢ Consultants and municipalities now propose roundabouts which is a change from a few years ago. Knowledge Gaps â¢ ConnDOTâs implementation strategy is working out well. â¢ On the technical side ConnDOT is learning as they get more experience. For instance, ConnDOT is now using granite on the truck apron. â¢ ConnDOT has expanded some of the information regard- ing roundabout design, but they mostly point to NCHRP Report 672 for details. Quality Control â¢ All the roundabouts built in Connecticut have gone through in-house design at ConnDOT. â¢ ConnDOT has spent a lot of time observing post construction. â¢ So far there has been a small pool of designers able to design roundabouts, but the pool of designers is growing. â¢ ConnDOT has identified additional details needed in the highway design manual. â¢ ConnDOT used an external reviewed for the first proposed roundabout in the state. Other â¢ ConnDOT is interested in seeing how phased implementation works. â¢ A roundabout proposed in Manchester, Connecticut will have rail going right through the middle of the intersection. â¢ There are potentially 20 to 25 planned roundabouts on state roads. â¢ The roundabouts that have been built, work! Georgia (GDOT) Roundabout Selection â¢ The majority of roundabouts are identified through the safety program. â¢ Many in design or construction have been identified by particular needs in the field, for example difficult intersection geometry or crash pattern. â¢ 1999 was the first roundabout in Georgia. A draft policy was developed in 2001 that was formally adopted in 2004. â¢ In 2008 the language changed from encourage to âpreferredâ and allowed multilane roundabouts. â¢ GDOT is now getting local municipalities asking for round abouts. â¢ The policy requires consideration of a roundabout during signal permit or any other type of project, which has triggered a lot of proposed roundabouts. Phased Implementation Approach â¢ If traffic volumes in the future-year analysis warrant a multi- lane roundabout GDOT recommends a phased approach. â¢ Most have been built with the outside footprint, circle, and splitter island geometry of the ultimate multilane roundabout. â¢ One roundabout was supposed to be phased but GDOT ended up building the full multilane roundabout due to an uptick in volumes prior to construction. â¢ Most projects use a 20 year design horizon to meet federal requirements.
78 â¢ GDOT uses a ten year window for considering a phased approach. â¢ GDOT prefers opening roundabouts as a single-lane round- about. If the roundabout will operate acceptably as a single- lane roundabout for at least seven to ten years, GDOT will open as a single-lane roundabout. Modifications to Existing Roundabouts â¢ So far GDOT has only modified roundabouts in the design process. Because of the restriction on building multilane roundabouts lifted in 2008, GDOT doesnât have a lot of multilane roundabouts to modify. Design Vehicle â¢ The design vehicle for roundabouts in Georgia is WB-67 truck. â¢ GDOT has aided municipalities with roundabouts not on the state highway system. â¢ In cases where a smaller design vehicle was used, GDOT encouraged hardscape on the center island. â¢ Depending on the routes GDOT can design for oversize- overweight (OSOW) vehicles, with a focus on over-length vehicles. â¢ GDOT knows the over-length vehicle routes but not the vehicle axle spacing. GDOT is now requiring the axle spac- ing to be able to model potential truck turning movements. â¢ The GDOT OSOW office tracks the over-length history and determines, based on the routes, if there is a need to accommodate OSOW vehicles, otherwise GDOT looks to use parallel routes. â¢ One example is a Kia plant being built; once the factory is done there is no longer a need to accommodate over-length vehicles. â¢ GDOT does not design to accommodate side by side truck movements, nor does GDOT design to allow full straddling. â¢ GDOT designs to allow a truck in the right lane to over-track but still leave room for a car in the adjacent lane. Accelerated, Low-Cost Roundabouts â¢ In District 1 GDOT used state forces to install a mini round- about. Modular curbing was used to define the center island and was backfilled with asphalt. â¢ If GDOT was to repeat the installation, GDOT would have used a more rigid curbing system. â¢ Project included widening on three of the four corners and a 90 foot inscribed circle diameter roundabout. â¢ The cost was $63,000 including full repaving and striping. â¢ GDOT has conducted two or three âquick responseâ projects that have $200k budget cap. â¢ GDOT used district maintenance resources and a general contractor. â¢ Contractor built central island and set the intersection grades and then GDOT did asphalt overlay on all approaches. â¢ Challenges were coordination between forces, and actual costs may have been higher, overall costs were probably closer to $300K. â¢ Another location is more temporary, using just rigid modular curb for the roundabout layout, and no paving. â¢ GDOT is procuring rigid modular curb, as most locations are on roadways that do not have curb and gutter. â¢ This practice has been effective at reducing queues and crashes. Implementation and Effectiveness of Policies â¢ The policy reads as a âshallâ condition, but there is some room to get around the policy. â¢ The policy could be stronger and require a clearer statement of why the roundabout was not chosen. â¢ An ICE policy would help. Knowledge Gaps â¢ There is not a lot of flexibility in available roundabout design guidance. â¢ With a decent design and good speed control, roundabouts have proven safety and operational benefits. â¢ Without ICE, GDOT engineers have to convince the GDOT project manager and highway design folks to get a round- about to the concept level. Otherwise, a signal will be installed with the safety benefits of a roundabout ignored. â¢ Some consultant peer reviews have made it difficult to implement due to increased costs due to consultant comments. â¢ GDOT would like know what design requirements could be relaxed (curb and gutter or illumination, for instance) to increase the cost-effectiveness. Quality Control â¢ GDOT does a peer review on most roundabouts. Public Rights-of-Way Accessibility Guidelines (PROWAG) â¢ We provide conduit under the road where the signal would go. Just the piece of conduit. Kansas (KDOT) Roundabout Selection â¢ Roundabout selection has been strictly based on crashes, but operations are considered. â¢ Requests from municipalities for gateway treatments are fairly frequent. â¢ From a local perspective, cities have used roundabouts as a traffic calming device in locations with less frequent and less severe crashes. â¢ Many roundabout locations are off of the highway system. Kansas has a reputation for roundabouts partially because of many local examples. â¢ Lawrence, Kansas, has a roundabouts first policy because of the positive impacts of roundabouts. Phased Implementation Approach â¢ For a phased approach KDOT builds the outside geometry and allows for expansion to the inside.
79 â¢ Partially because of recent experience with a multilane roundabout in Emporia, Kansas, multilane roundabouts are not viewed as favorable at the moment. Modifications to Existing Roundabouts â¢ A multilane roundabout in Emporia, Kansas was reconfig- ured to a single lane roundabout. A number of trucks were over turning, and confusion with navigation was identified as issues. Since the capacity was reduced, there havenât been further problems (converted 18 months ago). â¢ Agency has shifted focus to be supportive of the communityâs desires. Design Vehicle â¢ The design vehicle for roundabouts matches the design vehi- cle for the highway network in which the roundabout exists. â¢ Most roundabout designers are well aware of oversize/ overweight vehicle concerns as it is mentioned throughout the KDOT roundabout design guide. â¢ There is no standard super-load vehicle. â¢ WB-67 was the design vehicle in Lyndon, Kansas, but KDOT tweaked the design to allow rear-steer for larger loads, and to broaden the range of roundabouts. â¢ Wind energy has loads that are big and bulky but not heavy. These vehicles must obtain a permit for transport of the 130â150 foot loads. Accelerated, Low-Cost Roundabouts â¢ KDOT is not doing this, but there might be some local examples within Kansas. Knowledge Gaps â¢ KDOT used shoulders on a couple roundabouts, but believes curbing provides positive guidance for drivers. â¢ Most roundabouts are concrete pavement, and KDOT would like more information on the best ways to stage reconstruc- tion of concrete roundabouts. â¢ Experience in Emporia reinforced a phased approach. â¢ OSOW and wind energy vehicle accommodation are the two biggest design needs at the moment. Other â¢ KDOT hears from other states that the KDOT guide is being used for their design guidance. â¢ KDOT is still building dumbbell roundabouts because they are better with speed control than ovals and the cost of bridges is less. Maryland Roundabout Selection â¢ Roundabouts have become the default intersection form in Maryland. â¢ Roundabouts are mostly proposed for safety reason, but a few are capacity driven, and one in Mount Rainier, Maryland, was economic driven. â¢ Consultants working on development projects know SHA is going to require the evaluation of a roundabout, so theyâre proposing them as part of development project as well. â¢ Maryland has had their policy requiring evaluation for a while now. The policy is strictly enforced which has led to roundabouts becoming the default intersection choice. Phased Implementation Approach â¢ The Towson Circle and I-495/Ritchie-Marlboro Road interchange ramp terminal roundabouts were all built as two-lane multilane roundabouts, but planned to be expanded to three-lanes. Towson Circle was reduced to a hybrid single-lane/multilane roundabout a few years ago, and will never be expanded, and the Ritchie-Marlboro Road round- abouts were expanded to three lanes due to development pressure. â¢ Because of SHAâs experience with modifying many of the early multilane roundabouts, SHA attempts to open a roundabout as small as possible. â¢ If a roundabout will get at least five to ten years of service with a smaller configuration, SHA will open the roundabout smaller. Modifications to Existing Roundabouts â¢ The Towson Circle was reduced from a two-lane multilane roundabout to a hybrid single-lane/multilane roundabout. â¢ The roundabout at an interchange ramp terminal in Arundel Mills, Maryland was removed to allow a diverging diamond interchange to be constructed. â¢ Roundabouts near Fort Meade and in Odenton were both modified by reducing capacity. Design Vehicle â¢ SHA uses a WB-67 design vehicle as the default for all state routes. â¢ Many of the early roundabouts used a WB-50 design vehicle. While WB-67s can get through these roundabouts, markings around the intersections indicate they are not doing so with- out off-tracking on curbs or outside shoulders. (Although outside shoulders were used at many of Marylandâs early roundabouts, Maryland uses curb and gutter for all new roundabouts, and roundabout retrofit projects). Accelerated, Low-Cost Roundabouts â¢ SHA built a mini-roundabout using thermoplastic and tape at the intersection of US 50/Thompson Creek Road in Stevensville, Maryland. â¢ The roundabout cost about $50 thousand, and has been in place for five to ten years. â¢ SHA hasnât made a habit out of building more low-cost roundabouts, and credits the successful implementation of the roundabout in Stevensville to a low-speed environment, and an intersection without any real through movements. Knowledge Gaps â¢ Maryland acknowledges some early mistakes made in regards to roundabout design.
80 â¢ In particular, Maryland did not understand the potential for path overlap at multilane roundabouts, and has attempted to restripe or reduce the number of entering lanes to cor- rect the issue. Roundabout Cost â¢ All roundabouts in Maryland now have curb and gutter and illumination. This wasnât the case at many early roundabouts. â¢ In particular, maintenance of traffic is driving up the project cost at many roundabouts. Quality Control â¢ All roundabout designs are reviewed to ensure compliance with design guidelines (NCHRP Report 672). Public Rights-of-Way Accessibility Guidelines (PROWAG) â¢ Maryland is attempting to âdo the right thingâ and at a minimum installing conduit at all multilane crossings. Minnesota (MnDOT) Roundabout Selection â¢ MnDOT uses an ICE process at every intersection project. An ICE process has been used for six years in Minnesota. â¢ The intersection control is not pre-determined; the ICE process drives the selection. However, sometimes there are other reasons that drive the selection process, primarily safety. â¢ The process previously only had a signal warrant report but was later broadened to include roundabouts. Modifications to Existing Roundabouts â¢ Two roundabouts were modified from their original design. They were built using a 20-year traffic forecast for the design and a multi-lane roundabout was needed to accommodate the projected traffic. One location had performance issue immediately, the other had issues over the course of a few years. The traffic volumes at both locations were low enough that a single lane could have worked acceptably. One location was converted to a single-lane roundabout with striping and signing. At the other location, curbs were on two quadrants. â¢ There have been a few other instances of striping and signing changes. â¢ MnDOT is now considering more closely if a roundabout only marginally meets the threshold for multiple lanes, if so then MnDOT builds a single lane roundabout. Design Vehicle â¢ Design vehicle type varies based on the type of roadway facility. The design vehicle for trunk highways is a WB-62 truck and a low clearance trailer (lowboy). â¢ MnDOT verifies that the sign placement doesnât fall within the path of the vehicles. â¢ MnDOT is rethinking the truck apron height, for now, it is still four inches. Accelerated, Low-Cost Roundabouts â¢ No implementations from MnDOT so far, but in Minneapolis modular curbing was used for a temporary installation. Implementation and Effectiveness of Policies â¢ Per the engineering community, existing policies are pretty solid. The engineering community has not had any problems with implementing the policies from an engineering and technical point of view. â¢ One challenge is when a community wants a roundabout and a four way stop or traffic signal is proposed. There can be a lot of political will for a roundabout, but a four way stop may be practical and is a fraction of the cost. Knowledge Gaps â¢ How does MnDOT better design the roundabout for the opening year? How does MnDOT design something that works when it is opened and can be easily converted to accommodate future year volumes? â¢ A few instances where a signal was implemented 15 years ago and a roundabout is being considered. There are prop- erty damage only (PDO) crashes but how can we capture the existing value of the asset? Quality Control â¢ Most proposed roundabouts go through a roundabout review team made up of persons involved with designs. They make sure it is a sound design and this functions as a quality control check. Washington (WSDOT) Roundabout Selection â¢ Most roundabouts are brought forward because of local or DOT preference for roundabouts. â¢ Chapter 13 Intersection âtypeâ requires why a designer chose the intersection type: life cycle, mobility, and safety. Section 1300 is the policy, chapter 1320 is the roundabout design chapter. These both provide a lot of flexibility. â¢ Seeing the obvious benefits; WSDOT needed to legitimize the roundabout as an alternative, so the process was formal- ized. It was developed at the project traffic and operations sections. â¢ Roundabouts continued to be implemented because WSDOT had the right folks weighing in on the process. WSDOT learned that it was important to implement roundabouts when opportunities presented themselves. Modifications to Existing Roundabouts â¢ WSDOT has taken capacity out of multiplane roundabouts to minimize minor crash history: most are entering vehi- cles not yielding to circulating vehicles. These crashes are
81 typically property damage only (PDO) and modification involved reducing entry capacity. This was done at two locations. â¢ WSDOT rebuilt roundabouts at an interchange that was built in the late 1990s. Reconstruction included re-striping and semi-permanent curb. These locations had mostly PDO crashes. â¢ Not many modifications compared to the 105 WSDOT roundabouts that have been constructed. â¢ A roundabout was located on a bridge collapse detour route, and handled thru and left turns. Design Vehicle â¢ WSDOT first looks at the facility type, and then drills down to the individual movements within the intersection. â¢ WSDOT allows straddling of lanes as permitted by state law in its original form. â¢ With advent of practical design a WB-67 is not always needed, instead WSDOT looks at the individual movements. â¢ WSDOT recently modified the detail for the truck apron height from three inches to two inches. â¢ WSDOT engages region operations and traffic personnel. Section 1329 of the WSDOT design guidance references vehicle accommodations. Accelerated, Low-Cost Roundabouts â¢ WSDOT has done this at four locations, and all involved interim fixes in a weekend. â¢ These are typically done at compact roundabouts. â¢ No policy regarding this application but the traffic section has embraced them. â¢ They have been used at interchanges that are backing up on to the mainline. Local agencies are picking up on the idea as well. â¢ Primarily striping and signing, and the cost have been about $200,000 to $300,000 for the three county owned intersections. â These are good examples of interagency coordination. Implementation and Effectiveness of Policies â¢ In the near term WSDOT has been focused on the imple- mentation of roundabouts. Despite other successful projects, there is still resistance. â¢ Moving ahead, WSDOT is looking at life-cycle costs, espe- cially considering that signals require ongoing maintenance and retiming. Knowledge Gaps â¢ Knowledge gaps within WSDOT exist between Planning and Design. â¢ Design plans that are on the shelf are outdated in a year. â¢ Understanding that nodes are more important than the links. â¢ Speed is the not the defining factor of mobility. â¢ Access management could play a stronger role in transporta- tion planning. Quality Control â¢ All projects have a regional level review supported with headquarters supplied expertise. Public Rights-of-Way Accessibility Guidelines (PROWAG) â¢ WSDOT is working to make sure there is an active warning system at multi-lane crossings.
Abbreviations and acronyms used without definitions in TRB publications: A4A Airlines for America AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACIâNA Airports Council InternationalâNorth America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FAST Fixing Americaâs Surface Transportation Act (2015) FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers MAP-21 Moving Ahead for Progress in the 21st Century Act (2012) NASA National Aeronautics and Space Administration NASAO National Association of State Aviation Officials NCFRP National Cooperative Freight Research Program NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration NTSB National Transportation Safety Board PHMSA Pipeline and Hazardous Materials Safety Administration RITA Research and Innovative Technology Administration SAE Society of Automotive Engineers SAFETEA-LU Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (2005) TCRP Transit Cooperative Research Program TDC Transit Development Corporation TEA-21 Transportation Equity Act for the 21st Century (1998) TRB Transportation Research Board TSA Transportation Security Administration U.S.DOT United States Department of Transportation
TRANSPORTATION RESEARCH BOARD 5 0 0 F ifth S tre e t, N W W a s h in g to n , D C 2 0 0 0 1 A D D R ESS SER VICE R EQ UESTED NO N-PRO FIT O RG . U.S. PO STAG E PA ID CO LUM BIA, M D PER M IT NO . 88 ISBN 978-0-309-27208-7 9 7 8 0 3 0 9 2 7 2 0 8 7 9 0 0 0 0