National Academies Press: OpenBook

Roundabout Practices (2016)

Chapter: Chapter Three - Survey Results

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Suggested Citation:"Chapter Three - Survey Results ." National Academies of Sciences, Engineering, and Medicine. 2016. Roundabout Practices. Washington, DC: The National Academies Press. doi: 10.17226/23477.
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Suggested Citation:"Chapter Three - Survey Results ." National Academies of Sciences, Engineering, and Medicine. 2016. Roundabout Practices. Washington, DC: The National Academies Press. doi: 10.17226/23477.
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Suggested Citation:"Chapter Three - Survey Results ." National Academies of Sciences, Engineering, and Medicine. 2016. Roundabout Practices. Washington, DC: The National Academies Press. doi: 10.17226/23477.
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Suggested Citation:"Chapter Three - Survey Results ." National Academies of Sciences, Engineering, and Medicine. 2016. Roundabout Practices. Washington, DC: The National Academies Press. doi: 10.17226/23477.
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Suggested Citation:"Chapter Three - Survey Results ." National Academies of Sciences, Engineering, and Medicine. 2016. Roundabout Practices. Washington, DC: The National Academies Press. doi: 10.17226/23477.
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Suggested Citation:"Chapter Three - Survey Results ." National Academies of Sciences, Engineering, and Medicine. 2016. Roundabout Practices. Washington, DC: The National Academies Press. doi: 10.17226/23477.
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Suggested Citation:"Chapter Three - Survey Results ." National Academies of Sciences, Engineering, and Medicine. 2016. Roundabout Practices. Washington, DC: The National Academies Press. doi: 10.17226/23477.
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Suggested Citation:"Chapter Three - Survey Results ." National Academies of Sciences, Engineering, and Medicine. 2016. Roundabout Practices. Washington, DC: The National Academies Press. doi: 10.17226/23477.
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Suggested Citation:"Chapter Three - Survey Results ." National Academies of Sciences, Engineering, and Medicine. 2016. Roundabout Practices. Washington, DC: The National Academies Press. doi: 10.17226/23477.
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16 were built as part of projects overseen by their state agency on the state highway system. Table 5 displays the approximate total number of roundabouts, by type, as reported by each state responding to the questionnaire, and Table 6 displays the approximate total number of roundabouts on the state highway system, by type, as reported by each state. (The numbers of roundabouts provided by the states may differ from informa- tion included in the literature review in chapter two. Further, although this survey included definitions describing each type of roundabout, states may have interpreted terms differently.) As seen, the total number of roundabouts for all of the reporting states is approximately 2,707, with 1,997 single- lane roundabouts (74%) and 616 multilane roundabouts (26%). Washington and Wisconsin both report having more than 300 total roundabouts, while Missouri, North Carolina, and Washington each report having more than 200 single-lane roundabouts. Wisconsin is the only state reporting more than 100 multilane roundabouts, and is also the only state where the reported number of multilane roundabouts is more than half of the number of total roundabouts. Concerning roundabouts on a state highway system, Wisconsin is the only state reporting more than 200 in total; North Carolina, Virginia, and Wisconsin each report having 100 or more single-lane roundabouts on the state highway system. Wisconsin reports 147 multilane roundabouts on the state highway system; the next highest reported number, 30, is in Washington. Approximately 45% of the total roundabouts reported are on the state highway system. Approximately 42% of the reported single-lane roundabouts are on the state highway system, and approximately 60% of the reported multilane roundabouts. The states were asked to provide the environment (urban, suburban, or rural) in which mini-, single-lane, and multilane roundabouts were located in their states. The responses were generalized—all, some, most, or none—in an attempt to increase the response rate; and were converted to a numeri- cal score using a value of 1 for all, 0.67 for some, 0.33 for some, and 0 for none. Figure 23 is a visual representation of the proportion of mini-, single-lane, and multilane round- abouts in urban, suburban, and rural locations. As shown, the most common reported environment for all roundabout types is urban, with suburban environments also common for single-lane and multilane roundabouts. A higher proportion of mini-roundabouts are located in urban areas compared with This chapter outlines the results of the background informa- tion collected in a survey of all state agencies across the United States. The information was gathered from responses to a sur- vey questionnaire distributed to all members of the AASHTO Subcommittee on Traffic Engineering, which includes the state traffic engineers from the 50 states as well as Washington, D.C. and Puerto Rico. The survey was sent in February 2015, with follow-up reminders sent in March and April. Forty (40) states, or 80%, responded to the survey, as shown in Figure 21. The survey was modeled on portions of the 1998 NCHRP Synthesis 264 report, and where applicable, the results are com- pared. Although NCHRP Synthesis 264 recorded responses from 44 state agencies, only nine reported a roundabout in operation, under construction, or in design as of 1997. Of the 40 states that responded to the questionnaire for this effort, two states (Idaho and South Dakota) reported that their agency has not built a roundabout on the state highway system. How- ever, SDDOT reported that a roundabout has been planned or designed, but not yet built. (As discussed in the literature review chapter, all 50 states and the District of Columbia had a roundabout as of 2010, but some did not have a roundabout built under the purview of the state agency or the state highway system.) The data received in the NCHRP Synthesis 264 question- naire also included specific information about individual roundabouts in operation by state agencies and municipali- ties. Because of the larger number of roundabouts now in operation in the United States, this information was not rep- licated as part of this synthesis. To assess when individual states began constructing round- abouts, respondents were asked the approximate year the state agency built its first roundabout on the state highway system, not the year the first roundabout was constructed in their state. In some cases, respondents reported the year the first circular intersection was built on the state highway system. In these cases, the online database maintained by Kittelson & Associ- ates, Inc. (3). was consulted to identify the appropriate year. As shown in Figure 22, six state agencies had built round- abouts before 1999. By 2000, more than twice as many state agencies had built roundabouts (14 total), and by 2012, 38 of the 40 reporting state agencies had built a roundabout. States were asked to provide the approximate total number of mini-, single-lane, and multilane roundabouts in their state, and the approximate number of mini-, single-lane, and multi- lane roundabouts that their state has jurisdiction over and/or chapter three SURVEY RESULTS

17 single-lane and multilane roundabouts. Rural roundabouts are most likely to be single-lane roundabouts. ROUNDABOUT SELECTION States were asked to select the frequency in which they select roundabouts based on a set of common reasons, items from NCHRP Synthesis 264 supplemented by reasons identified by the study team and the panel for this synthesis. The follow- ing reasons of selection were provided, and states were asked to provide the frequency using a Likert-type rating scale— always, usually, about half the time, seldom, and none—of responses: • Aesthetic/urban design improvements • Higher capacity • Improved safety performance • Lower initial capital costs • Lower life-cycle costs • Lower speeds/traffic calming • Responding to request from elected official • Responding to request from local jurisdiction • Shorter vehicular delays. FIGURE 21 States responding to questionnaire. Alaska Arkansas California Connecticut Delaware Florida Georgia Illinois Indiana Iowa Kansas Kentucky Louisiana Maine Maryland Massachusetts Michigan Minnesota Mississippi Missouri Montana Nebraska Nevada New Hampshire New Mexico New York 1 1 1 1 1 North Carolina North Dakota Oregon Pennsylvania Rhode Island Texas Vermont Virginia Washington West Virginia Wisconsin Wyoming 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 FIGURE 22 Year state agency built their first roundabout on the state highway system.

18 States were also asked to provide additional reasons why roundabouts were selected in a comment field. Figure 24 dis- plays the most frequent reasons for the selection of round- abouts by state agencies. To provide a visual representation of the frequency of selection, a weighted score was applied to the responses using a value of 1 for always, 0.75 for usually, 0.5 for about half the time, 0.25 for seldom, and 0 for never. As shown, the primary reason for the selection of round- abouts is improved safety performance, selected with “always” or “usually” frequency by 33 of the 37 responses (89%). By comparison, 22% of respondents in NCHRP Synthesis 264 indicated “greater safety” as a major reason for building roundabouts. Shorter vehicular delays and higher capacity were the next most frequent responses, with 68% and 51% of respondents choosing “always” or “usually,” respectively. Several respondents indicated that the two answers could be combined, but they were separated to provide a com- parison with NCHRP Synthesis 264, where 14% and 8% of respondents chose “shorter delays” and “higher capacity,” respectively. On the other end of spectrum, the most frequent reasons that were cited as “seldom” (69%) or “never” (78%) for selecting roundabouts are “lower initial capital costs” and “responding to a request from elected official.” Several states provided written comments indicating other reasons why roundabouts were being considered. These responses included directives from the state agency to con- sider roundabouts, and the ability to minimize right-of-way impacts between intersections on narrow corridors or bridges. Reported Total Mini- Roundabouts Reported Total Single-Lane Roundabouts Reported Total Multilane Roundabouts Reported Total Roundabouts Alaska 3 20 9 32 Arkansas 0 25 0 25 California No answer 253 44 297 Connecticut 2 20 2 24 Delaware 1 11 1 13 Florida 4 13 11 28 Georgia 3 130 2 135 Idaho No answer No answer No answer — Illinois No answer No answer No answer — Indiana 0 122 39 161 Iowa 10 37 9 56 Kansas No answer 77 34 111 Kentucky 0 10 1 11 Louisiana No answer No answer No answer — Maine No answer 19 5 24 Maryland 10 114 37 161 Massachusetts No answer No answer No answer — Michigan 1 50 30 81 Minnesota 2 107 32 141 Mississippi 30 20 6 56 Missouri 5 200 20 225 Montana 1 20 12 33 Nebraska No answer 6 4 10 Nevada No answer 10 4 14 New Hampshire 0 28 6 34 New Mexico No answer 15 15 30 New York 2 100 25 127 North Carolina 0 229 18 247 North Dakota 10 2 No answer 12 Oregon 0 60 10 70 Pennsylvania 0 20 1 21 Rhode Island No answer 3 3 6 South Dakota No answer 3 0 3 Texas No answer No answer No answer — Vermont 1 12 1 14 Virginia No answer 145 15 160 Washington 9 210 85 304 West Virginia 0 5 4 9 Wisconsin 0 154 175 329 Wyoming No answer No answer No answer — Total 94 2,250 660 3,004 The number of roundabouts shown are numbers provided by each reporting state, and may differ from information included in the Literature Review section of this synthesis. — = Not Reported. TABLE 5 APPROXIMATE REPORTED TOTAL NUMBER OF ROUNDABOUTS WITHIN EACH REPORTING STATE

19 Reported Mini-Roundabouts on the State Highway System Reported Single-Lane Roundabouts on the State Highway System Reported Multilane Roundabouts on the State Highway System Reported Total Roundabouts on the State Highway System Alaska 0 11 7 18 Arkansas 0 0 4 4 California 0 11 12 23 Connecticut 0 3 1 4 Delaware 1 11 1 13 Florida 0 11 3 14 Georgia 2 20 0 22 Idaho No answer No answer No answer — Illinois No answer No answer No answer — Indiana 0 5 9 14 Iowa 0 7 0 7 Kansas 0 13 7 20 Kentucky No answer 9 9 Louisiana 0 22 1 23 Maine No answer 19 5 24 Maryland 1 53 24 78 Massachusetts 0 4 2 6 Michigan 0 10 15 25 Minnesota 0 24 9 33 Mississippi 0 3 3 6 Missouri 1 55 15 71 Montana 0 10 10 20 Nebraska No answer 6 2 8 Nevada No answer 4 No answer 4 New Hampshire 0 8 1 9 New Mexico No answer 10 10 20 New York 0 65 25 90 North Carolina 0 120 16 136 North Dakota No answer 1 No answer 1 Oregon 0 1 1 2 Pennsylvania 0 17 1 18 Rhode Island No answer No answer No answer — South Dakota 0 0 0 0 Texas No answer No answer No answer — Vermont 0 6 1 7 Virginia No answer 110 5 115 Washington 4 80 30 114 West Virginia 0 0 4 4 Wisconsin 0 100 147 247 Wyoming 0 5 0 5 Total 9 834 371 1,214 The number of roundabouts shown are numbers provided by each reporting state, and may differ from information included in the Literature Review section of this synthesis. — = Not Reported. TABLE 6 APPROXIMATE REPORTED TOTAL NUMBER OF ROUNDABOUTS ON THE STATE HIGHWAY SYSTEM WITHIN EACH REPORTING STATE Mini-Roundabouts Single-Lane Roundabouts Multilane Roundabouts Urban Suburban Rural FIGURE 23 Approximate reported proportion of roundabouts by location and type.

20 As with NCHRP Synthesis 264, state agencies that had not built a roundabout were asked to provide reasons. Because only one state agency had not built or planned to build a roundabout, compared with 35 state agencies in NCHRP Synthesis 264, the results are less meaningful. However, the one state did indicate it was considering the construction of roundabouts, whereas NCHRP Synthesis 264 reported only 30% of states without a roundabout in the state system were considering their construction. States were also asked whether their state agency had installed a roundabout in a location that had previously expe- rienced one or more fatal crashes; as shown in Table 7, 23 of the 38 (61%) responded affirmatively. ROUNDABOUT COSTS States provided the approximate planning-level cost estimate (for use in a screening or feasibility level estimate) for mini-, single-lane, and multilane roundabouts in their states, and asked to limit their responses to “single-purpose” inter section projects. The planning-level cost estimate was intended to provide an estimate for the total cost for opening a round- about. However, it is possible that states may have misinter- preted the question, and provided only the construction cost rather than the total cost including the planning, design, and construction of the roundabout. As shown in Table 8, the states’ planning estimates for a mini-roundabout range from $50,000 to $1 million, with an average of $249,000. The planning-level cost estimates reported by states for a single-lane roundabout is higher, rang- ing from $100,000 to $5 million, with an average of $1.30 mil- lion. Highest are the costs of multilane roundabouts, estimated at $200,000 and $6 million, with an average of $2.05 million. PUBLIC OUTREACH States were asked to list the types of public outreach materials they have developed, and the results are shown in Figure 25. The question did not specify whether the public outreach material was project related or for general education pur- poses. As shown, 30 of the 39 reporting states (77%) have developed a roundabout website, 33 (85%) have developed a flyer and/or pamphlet, and 21 (54%) have developed a video. States were also asked to list other types of public outreach they had developed. Several states responded by saying they had included guidance about roundabouts on state highway maps, and several also mentioned TV and radio commercials and video animations. Lastly, one state also added newspaper articles and roundabout information included in the state’s commercial drivers manual, and another state added that it has used a mall kiosk, bus rides, and simulator events. Four 0 5 10 15 20 25 30 Im proved safety perfo rm a n ce Shorter v ehicular delays H igher capacity Low er sp eeds/traffic calm ing Low er life -cy cle co sts R esponding to req u est from lo cal jurisdictio n A esth etic/u rba n d esig n im pro v em ents R esponding to req u est fro m elected official L o w er initial capital co sts Always Usually About half the time Seldom Never Weighted Response Score FIGURE 24 Number of responses indicating the frequency of the use of primary reasons for the selection of roundabouts. Response Number % Yes 23 61 No 8 21 Don’t know 7 18 Total 38 100 TABLE 7 STATE AGENCIES THAT INSTALLED A ROUNDABOUT AT A LOCATION THAT HAD PREVIOUSLY EXPERIENCED ONE OR MORE FATAL CRASHES

21 of the reporting states (10%) indicated they had not devel- oped any public outreach material. As shown in Table 9, nearly all the states—37 of 38—use public information open houses, and over half use all of the strategies listed. In particular, states that use public informa- tion open houses list “attendance from agency staff.” Over 90% of the states include traffic engineers involved in the project, and 95% of the states prepare a presentation. ROUNDABOUT PERFORMANCE ANALYSIS This section provides an overview of the methods used by state DOTs to analyze the operational performance of round- abouts, and those used to analyze their safety performance. Operational Performance Analysis The states provided the operational performance analysis model(s) used or permitted by their state agencies. As shown in Table 10, 26 of the 36 states responding to the question (72%) use at least one form of the HCM 2010 model, with 22 states using the base HCM 2010 model and 12 states using the HCM 2010 model calibrated to local conditions. At least one form of the SIDRA Standard model is used by 27 of the 36 states responding to the question (75%), with 20 states using the SIDRA Standard model with the environment factor, and 13 states using the model without the environment factor. Eight of the reporting states use United Kingdom (UK) equa- tions, with four states using equations that are not calibrated to local conditions, and four using UK equations that are cali- brated to local conditions. Some form of microsimulation is used by 22 of the 36 reporting states (61%). The states also provided information on the software tools used by their state agency to determine the operational perfor- mance of a roundabout. The list of software tools was taken from the Roundabout Software Evaluation (39) report, with non-English language software tools removed, and new soft- ware tools available since the report was published added. As shown in Table 11, SIDRA is the most widely-used soft- ware tool, used by 28 of the 37 state agencies responding to the question, followed by Synchro and HCS. In addition to commercially available software packages, several states Roundabout Type Mini-roundabout Single-lane roundabout Multilane roundabout Number of Responses 10 29 25 Minimum $50,000 $100,000 $200,000 Average $249,000 $1,296,034 $2,048,000 Maximum $1,000,000 $5,000,000 $6,000,000 TABLE 8 PLANNING LEVEL COST ESTIMATE (SCREENING OR FEASIBILITY LEVEL ESTIMATE) BY ROUNDABOUT TYPE AS REPORTED BY STATE AGENCY Website Flyer and/or pamphlet Video No Material Developed 0 5 10 15 20 25 30 35 FIGURE 25 Number of state agencies developing types of public outreach material as reported by state agency.

22 have developed their own tools, including spreadsheets implementing HCM 2010 equations. Further, several state representatives commented that they specify different tools for the analysis of different time periods (existing versus future), or double-check results using a different tool if the capacity threshold is in question. Safety Analysis States were asked how their state analyzes safety performance at roundabouts. As shown in Table 12, five states (13%) do not typically analyze safety performance at roundabouts. Of the 38 responding states, 19 use either crash modification factors or crash reduction factors to analyze the safety performance at roundabouts, and 17 use the Highway Safety Manual predic- tive methodology. (States were allowed to select more than one response.) Five states have also developed state-specific procedures, and two use information published by the Insur- ance Institute for Highway Safety (IIHS). ROUNDABOUT DESIGN This section provides the results of the survey concerning the use of NCHRP Report 672, the use of a phased roundabout design approach, design-vehicle accommodations, and illu- mination at roundabouts. Software Tool Reporting State Agencies Using Software Tool % ARCADY 3 8 HCS 19 51 RODEL 9 24 SIDRA 28 76 State Agency-developed Tool 3 8 Synchro 20 54 VISTRO 2 5 Other* 4 11 *In comments, three listed VISSIM and 1 indicated Excel Spreadsheet. Public Information Open House Strategy Reporting States Agencies Using Strategy % Attendance from “high-ranking” agency official 19 50 Attendance from agency staff 37 97 Attendance from roundabout design team 34 89 Attendance from traffic engineers involved in the project 35 92 Attendance from transportation planners involved in the project 26 68 Charts, figures, etc... on display boards 33 87 Flyer and/or pamphlet 34 89 Presentations 36 95 Question and answer session (town hall meeting) 28 74 Scaled plan sets with vehicle models 21 55 Video 29 76 Video of roundabout simulation 31 82 Public information open houses not used 1 3 TABLE 9 PUBLIC INFORMATION OPEN HOUSE STRATEGIES REPORTED AS USED BY STATE AGENCIES Model Reporting State Agencies Using Model % HCM 2010 Model 26 72 Base HCM 2010 Model 22 61 HCM 2010 Model calibrated to local conditions 12 33 HCM 2010 Model calibrated to non-local conditions 2 6 SIDRA Standard Model 27 75 SIDRA Standard Model with Environment Factor 20 56 SIDRA Standard Model without Environment Factor 13 36 UK Equations 8 22 UK Equations uncalibrated 4 11 UK Equations calibrated 4 11 Microsimulation 22 61 Other 0 0 TABLE 10 OPERATIONAL PERFORMANCE MODELS REPORTED AS USED BY STATE AGENCIES TABLE 11 OPERATIONAL ANALYSIS SOFTWARE TOOLS REPORTED AS USED BY STATE AGENCIES

23 Use of NCHRP Report 672 States were asked the extent to which their agency uses NCHRP Report 672 for roundabout design guidelines. As shown in Table 13, 11 states use only NCHRP Report 672, 10 use material from other sources to supplement it, and 13 have developed their own guidance to supplement it. Three states either do not use, or rarely use, NCHRP Report 672, with two using materials from other sources, and one state having developed its own guidelines. However, two of the three states that rarely use NCHRP Report 672 indicated that this report had been a primary source in the development of their own design guidance. Phased Roundabout Implementation States provided information on the use of a phased roundabout implementation approach over the project life (e.g., a single-lane roundabout expanded to a multilane roundabout). As shown in Table 14, 23 of the reporting 37 states use a phased approach. If state agencies indicated they used a phased implementa- tion approach, they were asked if they had criteria for deter- mining when such an approach should be used. Eleven (11) states indicated they did have criteria. Although the criteria vary, five of the 11 indicated that they will move forward with a single-lane roundabout if the roundabout is projected to operate “acceptably” for at least 10 years. Three others indi- cated the determination was on a case-by-case basis. Roundabout Design Life States also provided information on the roundabout design life used to determine the ultimate design. As shown in Table 15, 29 of the 38 responding state agencies use a fixed duration for the design life, with seven setting the design-life on a case-by- case basis, and four using a practical design policy. (States were allowed to select more than one response.) No state agencies cited specific criteria or a fixed design year. The states using a fixed duration were asked to provide the number of years (Figure 26). Several states indicated more than one design life duration, but the clear majority use 20 years for the design life. States indicating they use a case-by-case basis or a practi- cal design policy were asked to share how frequently they use various design life options. As shown in Figure 27, the most common design life is also 20 years. A design life of five years, Safety Analysis Procedure Reporting State Agencies Using Safety Analysis Procedure % Our state does not typically estimate or predict safety at roundabouts 5 13 Highway Safety Manual predictive methodology 17 45 Crash modification factors or crash reduction factors (uncalibrated) 19 50 Crash modification factors or crash reduction factors (calibrated to local conditions) 9 24 Other Responses 7 18 Insurance Institute for Highway Safety 2 5 State agency-specific procedure 5 13 TABLE 12 SAFETY ANALYSIS PROCEDURES REPORTED AS USED BY STATE AGENCIES Use of NCHRP Report 672 to Provide Design Guidance Reporting Number of State Agencies NCHRP Report 672 is the only source of design guidance. 11 Material from other sources supplements NCHRP Report 672 10 Our state has developed guidance to supplement NCHRP Report 672 13 Our state uses material from other sources, and does not use, or rarely uses, NCHRP Report 672 2 Our state has developed separate guidance and does not use, or rarely uses, NCHRP Report 672 1 Total 37 TABLE 13 STATE AGENCY USE OF NCHRP REPORT 672 AS REPORTED BY STATE AGENCY State Agency Use of a Phased Implementation Approach to Multilane Roundabouts Reporting Number of State Agencies Yes 23 No 14 Total 37 TABLE 14 REPORTED STATE AGENCY USE OF A PHASED IMPLEMENTATION APPROACH TO MULTILANE ROUNDABOUTS

24 or more than 20 years, is not common, and a design-life of 10 years is used by only a few state agencies. Design Vehicle Accommodation States were asked if their agency had developed guidance on the accommodation of large vehicles (trucks, emergency Design-Life Criteria Reporting State Agency Responses % Case-by-Case Basis 7 18 Practical Design Policy 4 11 Specific Criteria 0 0 Fixed Design Year 0 0 Fixed Duration 29 76 TABLE 15 ROUNDABOUT DESIGN LIFE CRITERIA REPORTED AS USED BY STATE AGENCIES 0 5 10 15 20 25 30 10 years 15 years 20 years 25 years 30 years FIGURE 26 Number of reporting states indicating roundabout design life used by state agencies with a fixed design-life duration. 0 1 2 3 4 5 6 7 5 years 10 years 20 years Over 20 years Always Usually Sometimes Seldom Never FIGURE 27 Frequency of the use of design life duration options for reporting states using case-by-case basis or a practical design policy.

25 vehicles, farming equipment, oversize/overweight vehicles, etc.) at roundabouts. Of the 38 states responding to the ques- tion, 19 (50%) indicated their agency had developed guid- ance. Several states simply guide designers to use a WB-67 design vehicle, and at least four states are currently in the process of developing guidance for the accommodation of large vehicles. Illumination at Roundabouts States were asked if they follow developed standards/guidance on the illumination of roundabouts, and all 38 reporting states indicated they do follow developed guidance. However, one state indicated that although it uses the IES Design Guide, it does not require the illumination of roundabouts. States were asked to choose between the AASHTO Roadway Light- ing Guide, IES Design Guide, NCHRP Report 672, a state- specific standard, or other guidance. However, because NCHRP Report 672 illumination guidance is based on the IES Design Guide, responses shown in Table 16 for either choice were combined. As shown in Table 16, 20 of the 37 states that responded use the AASHTO Roadway Lighting Guide, and 20 use NCHRP Report 672 (IES Design Guide). Six states have developed their own state-specific standard, and eight use an alterna- tive approach, such as Roundabouts: An Informational Guide (1st Edition), and AASHTO’s 1984 An Informational Guide for Roadway Lighting. Illumination Standard/Guidance Reporting State Agencies Using Particular Illumination Standard/Guidance % AASHTO Roadway Lighting Design Guide 20 54 NCHRP Report 672 (IES Design Guide for Roundabout Lighting) 20 54 State-Specific Standard 6 16 Other 8 22 TABLE 16 ILLUMINATION STANDARD/GUIDANCE REPORTED AS USED BY STATE AGENCIES

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TRB's National Cooperative Highway Research Program (NCHRP) Synthesis 488: Roundabout Practices summarizes roundabout policies, guidance, and practices within state departments of transportation (DOTs) as of 2015. The synthesis may be used as a reference for state agencies that are creating or updating their roundabout and intersection control policies.

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