National Academies Press: OpenBook
« Previous: Chapter 29: Bicyclists
Page 161
Suggested Citation:"Chapter 30: Roundabouts." National Academies of Sciences, Engineering, and Medicine. 2022. Human Factors Guidelines for Road Systems 2021 Update, Volume 1: Updated and New Chapters. Washington, DC: The National Academies Press. doi: 10.17226/26473.
×
Page 161
Page 162
Suggested Citation:"Chapter 30: Roundabouts." National Academies of Sciences, Engineering, and Medicine. 2022. Human Factors Guidelines for Road Systems 2021 Update, Volume 1: Updated and New Chapters. Washington, DC: The National Academies Press. doi: 10.17226/26473.
×
Page 162
Page 163
Suggested Citation:"Chapter 30: Roundabouts." National Academies of Sciences, Engineering, and Medicine. 2022. Human Factors Guidelines for Road Systems 2021 Update, Volume 1: Updated and New Chapters. Washington, DC: The National Academies Press. doi: 10.17226/26473.
×
Page 163
Page 164
Suggested Citation:"Chapter 30: Roundabouts." National Academies of Sciences, Engineering, and Medicine. 2022. Human Factors Guidelines for Road Systems 2021 Update, Volume 1: Updated and New Chapters. Washington, DC: The National Academies Press. doi: 10.17226/26473.
×
Page 164
Page 165
Suggested Citation:"Chapter 30: Roundabouts." National Academies of Sciences, Engineering, and Medicine. 2022. Human Factors Guidelines for Road Systems 2021 Update, Volume 1: Updated and New Chapters. Washington, DC: The National Academies Press. doi: 10.17226/26473.
×
Page 165
Page 166
Suggested Citation:"Chapter 30: Roundabouts." National Academies of Sciences, Engineering, and Medicine. 2022. Human Factors Guidelines for Road Systems 2021 Update, Volume 1: Updated and New Chapters. Washington, DC: The National Academies Press. doi: 10.17226/26473.
×
Page 166
Page 167
Suggested Citation:"Chapter 30: Roundabouts." National Academies of Sciences, Engineering, and Medicine. 2022. Human Factors Guidelines for Road Systems 2021 Update, Volume 1: Updated and New Chapters. Washington, DC: The National Academies Press. doi: 10.17226/26473.
×
Page 167
Page 168
Suggested Citation:"Chapter 30: Roundabouts." National Academies of Sciences, Engineering, and Medicine. 2022. Human Factors Guidelines for Road Systems 2021 Update, Volume 1: Updated and New Chapters. Washington, DC: The National Academies Press. doi: 10.17226/26473.
×
Page 168
Page 169
Suggested Citation:"Chapter 30: Roundabouts." National Academies of Sciences, Engineering, and Medicine. 2022. Human Factors Guidelines for Road Systems 2021 Update, Volume 1: Updated and New Chapters. Washington, DC: The National Academies Press. doi: 10.17226/26473.
×
Page 169
Page 170
Suggested Citation:"Chapter 30: Roundabouts." National Academies of Sciences, Engineering, and Medicine. 2022. Human Factors Guidelines for Road Systems 2021 Update, Volume 1: Updated and New Chapters. Washington, DC: The National Academies Press. doi: 10.17226/26473.
×
Page 170
Page 171
Suggested Citation:"Chapter 30: Roundabouts." National Academies of Sciences, Engineering, and Medicine. 2022. Human Factors Guidelines for Road Systems 2021 Update, Volume 1: Updated and New Chapters. Washington, DC: The National Academies Press. doi: 10.17226/26473.
×
Page 171
Page 172
Suggested Citation:"Chapter 30: Roundabouts." National Academies of Sciences, Engineering, and Medicine. 2022. Human Factors Guidelines for Road Systems 2021 Update, Volume 1: Updated and New Chapters. Washington, DC: The National Academies Press. doi: 10.17226/26473.
×
Page 172
Page 173
Suggested Citation:"Chapter 30: Roundabouts." National Academies of Sciences, Engineering, and Medicine. 2022. Human Factors Guidelines for Road Systems 2021 Update, Volume 1: Updated and New Chapters. Washington, DC: The National Academies Press. doi: 10.17226/26473.
×
Page 173

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.

HFG ROUNDABOUTS VERSION 2.1 30-1 C CHAPTER 30 ROUNDABOUTS Reducing Vehicle Speeds Approaching Roundabouts .............................................................. 30-2 Increasing Driver Yielding Rates for Pedestrians at Roundabouts ............................................ 30-4 Guide Signing at Roundabouts .................................................................................................. 30-6 Accommodations for Bicyclists at Roundabouts ....................................................................... 30-8 Countermeasures for Improving Accessibility for Visually Impaired Pedestrians at Roundabouts ........................................................................................................................ 30-10 Roundabout Lighting ............................................................................................................... 30-12

HFG ROUNDABOUTS VERSION 2.1 30-2 REDUCING VEHICLE SPEEDS APPROACHING ROUNDABOUTS Introduction Reducing vehicle speeds approaching roundabouts provides more time for drivers to react to the presence of pedestrians and bicyclists crossing a roundabout approach or traveling through the roundabout. Research has shown that reducing vehicle speeds entering, traversing, and exiting roundabouts increases yielding rates to other vehicles, bicycles, and pedestrians. Lower vehicle speeds also reduce the severity of crashes that do occur and can make crashes with pedestrians and bicyclists more survivable. Furthermore, reduced motor vehicle speeds may reduce the incidence of sideswipe crashes, run-off-road crashes, and turning crashes at roundabouts, as well as the severity of angle crashes. Design Guidelines DESIGN STRATEGIES TO REDUCE VEHICLE SPEEDS APPROACHING ROUNDABOUTS Design Element Strategy Sight Distance Provide no more than the minimum required sight distance (1,2,3). Reducing intersection sight distance reduces approach speeds and speed differential between vehicles. Reducing upstream and circulating approach sight distances also reduces approach speed differentials. Much care is needed to make sure sight distance is adequate for safe roundabout operations. Minimum required sight distance values can be found in NCHRP Report 672. Lane Width Narrow the approach and exit lane widths to reduce vehicle speeds (2). Vehicle Path Radius at Entry and Exit Reduce the vehicle path radius at the entry and exit of a roundabout to decrease approach and exit speeds of vehicles (4). Inscribed Circle Diameter Reduce the inscribed circle diameter to reduce circulating vehicle speeds. Care is needed to make sure the diameter is large enough to accommodate the design vehicle (2). Transverse Rumble Strips Install transverse rumble strips on roundabout approaches to reduce approach speeds (5). However, approach speed differentials may increase. Guide Posts Install evenly- or unevenly-spaced guide posts adjacent to the vehicle path entering a roundabout and within a roundabout to reduce vehicle speeds (6). Center Island Landscaping Installing trees in the center island to reduce vehicle speeds and speed differentials (7). Intersection sight distance at a roundabout (2) The figure at left presents two types of sight distances at a roundabout. d1 is the sight distance needed to see and react to a vehicle on an upstream entry from a downstream entry, while d2 is the sight distance needed to see and react to a vehicle within the circulating roadway when entering the roundabout. Based Primarily on Expert Judgment Based Equally on Expert Judgment and Empirical Data Based Primarily on Empirical Data

HFG ROUNDABOUTS VERSION 2.1 30-3 Discussion Pedestrian crossings at roundabouts can be more challenging than at traditional intersections for several reasons. If suitable gaps are available, drivers do not have to stop on the roundabout approach before merging into circulating traffic. The driver’s attention is generally focused to the left to evaluate available gaps, while pedestrians may be crossing from the right. Pedestrians crossing an exiting roundabout leg may not be visible to exiting drivers, who are often accelerating out of the roundabout, until they are in close proximity due to landscaping or other occlusions. Limiting vehicle speed provides more perception-reaction time for drivers to identify pedestrians and avoid crashes, and also reduces the severity of crashes that occur. Bikes often merge into the travel lane from a bike lane or shoulder at roundabout approaches and travel with traffic through the roundabout. Bicycle safety is improved when the difference between motor vehicle speeds and bicycle speeds is minimized. Design Issues It seems counterintuitive to design intersection or roadway elements with minimal sight distance for the sake of improving safety. In the case of roundabouts, research has shown that excessive intersection sight distance can lead to higher vehicle speeds, which in turn may reduce the safety of the intersection for all road users (1, 2, 3). It is recommended to design to the minimum required intersection sight distance on each approach. Restricting lane width, inscribed diameter, and entry and exit turning radii can all have major implications on how larger vehicles navigate roundabouts (2, 4). It is necessary to consider larger design vehicles if appropriate for the site. There are, however, design treatments for roundabouts to accommodate larger design vehicles without reducing the effectiveness of speed reduction strategies, such as mountable curbs. Adjacent land use should be considered prior to the installation of transverse rumble strips on roundabout approaches. For some land uses, especially residential areas and schools, the sound produced by rumble strips can be viewed as a nuisance. Sinusoidal rumble strips may be a potential solution in these situations (8). Guideposts and landscaping may require much maintenance. Guideposts in roundabouts have the potential to be damaged by vehicles. Replacement of damaged guideposts will be needed occasionally. Landscaping involving plants must be maintained and/or replaced routinely. In addition, some landscaping options such as trees may increase fixed object crashes (2, 7). Cross References Accommodations for Bicyclists at Roundabouts, 30-8 Countermeasures for Improving Accessibility for Visually Impaired Pedestrians at Roundabouts, 30-10 Increasing Driver Yielding Rates for Pedestrians at Roundabouts, 30-4 References 1. Angelastro, M., K. Ozbay. (2010) The Influence of Driver Sight Distance on Crash Rates and Driver Speed at Modern Roundabouts in the United States. ITE Journal, Vol. 80, Issue 7, Institute of Transportation Engineers, Washington, DC. 2. Rodegerdts, L., Bansen, J., Tiesler, C., Knudsen, J., Myers, E., Johnson, M., . . . O'Brien, A. (2010). NCHRP Report 672: Roundabouts: An Informational Guide. Second Edition. Transportation Research Board of the National Academies, Washington, DC. 3. Zirkel, B., S. Park, J. McFadden, M. Angelastro, L. McCarthy. (2013) Analysis of Sight Distance, Crash Rate, and Operating Speed Relationships for Low-Volume Single-Lane Roundabouts in the United States. Journal of Transportation Engineering, American Society of Civil Engineers, Reston, VA. 4. Arndt, O., R. Troutbeck. (1988). Transportation Research Circular E-C003: Relationship Between Roundabout Geometry and Accident Rates. TRB, National Research Council, Washington DC. 5. Isebrands, H., S. Hallmark, N. Hawkins. (2014). Effects of Approach Speed at Rural High-Speed Intersections: Roundabouts Versus Two-Way- Stop Control. Transportation Research Record: Journal of the Transportation Research Board, No. 2402, pp.67-77. 6. Rossi, R., M. Gastaldi, F. Biondi, C. Mulatti. (2013). Oppel-Kundt Illusion and Lateral Optic Flow Manipulation in Affecting Perceived Speed in Approaching Roundabouts: Experiments with a Driving Simulator. TRB 92nd Annual Meeting Compendium of Papers, Transportation Research Board, Washington, DC. 7. Schurr, K., J. Abos-Sanchez. (2007). Effects of Central Island Landscaping at Single-Lane Roundabouts. Proceedings of the European Transport Conference 2007, Leiden, The Netherlands. 8. Horne, D., Jashami, H., Hurwitz, D. S., Monsere, C. M., and Kothuri, S. (2019). Mitigating roadside noise pollution: A comparison between rounded and sinusoidal milled rumble strips. Transportation Research Part D: Transport and Environment, 77, pp. 37-49. DOI:10.1016/j.trd.2019.10.006.

HFG ROUNDABOUTS VERSION 2.1 30-4 INCREASING DRIVER YIELDING RATES FOR PEDESTRIANS AT ROUNDABOUTS Introduction Drivers generally do not stop when entering a roundabout if there is a sufficient gap in traffic circling within the roundabout. Drivers are often looking to their left, focused on evaluating gaps, as they approach a roundabout and are not always aware of pedestrians approaching a crossing from the right. Upon exiting a roundabout, there may be fewer demands on drivers’ attention, but drivers are often accelerating out of the roundabout, making it more difficult to stop quickly for a pedestrian in a crossing. In addition, the available sight distance to a crossing pedestrian may be less at a roundabout exit than at the entrance, since the driver is not directly facing the crossing until they exit the roundabout. Design Guidelines COUNTERMEASURES FOR INCREASING DRIVER YIELDING RATES FOR PEDESTRIANS AT ROUNDABOUTS Countermeasure Description Increase driver awareness of crossing pedestrians at roundabout exits Install beacon—Pedestrian Hybrid Beacon (PHB) or Rectangular Rapid Flashing Beacon (RRFB)—at the exit leg of multilane roundabouts, and consider locating the beacon and crosswalk further from the beginning of the exit leg than the typical 20-ft distance (1). Improve visibility and conspicuity of pedestrian crossings at roundabouts Use high-visibility crossing treatments and signs to bring drivers’ attention to the possibility of a pedestrian crossing the roundabout approaches and exits. Increase sight distance to pedestrian crossings Ensure that good sight lines exist between drivers and pedestrians at the roundabout exit, since roundabout exits tend to have a higher percentage of vehicles that do not yield to pedestrians than roundabout entries (2). Reduce vehicle speeds at roundabout exits Use design features that discourage high acceleration out of the roundabout. Slower exit speeds provide more perception-reaction time for drivers to identify and yield to a pedestrian crossing a roundabout exit.  Tangential exit alignment: the large exit radius provides clear sight lines and visibility of pedestrians at the crosswalk but may encourage higher exit speeds.  Curvilinear exit alignment: the small exit radius reduces vehicle speeds exiting the roundabout. Roundabout with Pedestrian Hybrid Beacon and Longitudinal Markings at the Crosswalk Source: Adapted from MUTCD (3) Roundabout with Single-Lane Tangential Exit Alignment and Two-Lane Curvilinear Exit Alignment Source: Adapted from Rodegerdts et al., (2010 (4)) Based Primarily on Expert Judgment Based Equally on Expert Judgment and Empirical Data Based Primarily on Empirical Data

HFG ROUNDABOUTS VERSION 2.1 30-5 Discussion Beacon Installation and Crosswalk Location: Several studies have found better driver yielding behavior at crosswalks at roundabout entries than at crosswalks at roundabouts exits (2, 5, 6). Researchers have offered at least two possible explanations for this difference (2, 6): Drivers decelerate at the roundabout approach and accelerate at the roundabout exit. When approaching a roundabout, drivers may mentally be prepared to yield the right-of-way to any and all perceived conflicts, including pedestrians within or near a crosswalk. In contrast, when exiting a roundabout, drivers may behave as if the right-of-way they had within the roundabout continues upon exiting the roundabout, making them less likely to yield to pedestrians. To improve driver yielding at roundabout exits, consideration may be given to installation of a beacon. A driving simulator study (1) showed that installation of a PHB or RRFB significantly increases driver yielding rates at the exit leg of multilane roundabouts. The yielding rate was further increased when relocating the treatment (and crosswalk) further from the beginning of the exit leg. Relocating the crosswalk, without installing a beacon, does not provide a significant increase in driver yielding rate. The yielding rate resulting from the PHB (with solid red indication) was significantly higher than that of the RRFB, which only has a flashing yellow beacon. Sight Distance to Crosswalk: Driver sight distance likely impacts yielding behavior, particularly where sight distance is at or near the minimum recommended stopping sight distance (1). This may explain why yield rates are greater at roundabout entries, where crosswalks are often more visible, than at roundabout exits. It also suggests that increasing sight distance to pedestrians waiting at a crosswalk is likely to improve driver yielding at that crosswalk. High-Visibility Crossing Treatments: Crosswalk markings should be installed across the entrance and exit of each leg of a roundabout and across any right-turn bypass lanes. Crosswalk markings that are longitudinal to the flow of traffic are recommended. Longitudinal markings provide a higher degree of visibility and are less likely to be confused with the entrance line or the yield line (2). Pedestrian Crossing signs (W11-2 (3)) may be used at pedestrian crossings at roundabout entries and exits, and should be used at all pedestrian crossings at multilane entries, multilane exits, and right-turn bypass lanes. Pedestrian Crossing signs may be supplemented with a diagonal downward pointing arrow plaque (W16-7 (3)) showing the location of the crossing. Roundabout Exit Geometry: Small-radius, curvilinear exit alignments generally result in lower exit speeds than do larger-radius, tangential exit alignments. At single-lane roundabouts, it is acceptable to use a minimal exit radius in order to control exit speeds. Minimal exit radii are discouraged, however, at multilane roundabout exits (2). Design Issues When locating the pedestrian crossing, especially at roundabout exits, designers must balance the desire to provide adequate sight distance and visibility of the crossing with the need to keep vehicle speeds low at the crossing location. Crossing placed further downstream may provide more time for the driver to recognize the presence of the crossing, but it also provides more time for the vehicle to gain speed. In addition, the crosswalk placement must not be so inconvenient for pedestrians that they choose to cross at unmarked locations to reduce their travel time. Cross References Speed-Calming Countermeasures at Crosswalks, 28-6 Improving Pedestrian Visibility and Conspicuity at Crosswalks, 28-8 Selecting Beacons to Improve Pedestrian Conspicuity at Crosswalks, 28-10 References 1. Salamati, K., Schroeder, B., Rouphail, N. M., Cunningham, C., Zhang, Y., and Kaber, D. (2012). Simulator Study of Driver Responses to Pedestrian Treatments at Multilane Roundabouts. Transportation Research Record: Journal of the Transportation Research Board, No. 2312, pp. 67–75. 2. Rodegerdts, L., Blogg, M., Wemple, E., Myers, E., Kyte, M., Dixon, M. P., . . . Carter, D. (2007). NCHRP Report 572: Roundabouts in the United States. Transportation Research Board, Washington, DC. 3. Federal Highway Administration. (2012). Manual on uniform traffic control devices for streets and highways. 2009 edition with revision numbers 1 and 2 incorporated. Washington, DC. 4. Rodegerdts, L., Bansen, J., Tiesler, C., Knudsen, J., Myers, E., Johnson, M., . . . O'Brien, A. (2010). NCHRP Report 672: Roundabouts: An Informational Guide. Second Edition. Transportation Research Board of the National Academies, Washington, DC. 5. Findley, D., Searcy, S., Salamati, K., Schroeder, B., Williams, B., Bhagavathula, R., and Rodegerdts, L. (2015). Accelerating roundabout implementation in the United States: Volume VI of VII - investigation of crosswalk design and driver behaviors (Report No. FHWA-SA-15-074). Washington, DC: Federal Highway Administration. 6. Salamati, K., Schroeder, B. J., Geruschat, D. R., and Rouphail, N. M. (2013). Event-Based Modeling of Driver Yielding Behavior to Pedestrians at Two-Lane Roundabout Approaches. Transportation Research Record: Journal of the Transportation Research Board, No. 2389, pp. 1–11.

HFG ROUNDABOUTS VERSION 2.1 30-6 GUIDE SIGNING AT ROUNDABOUTS Introduction While the use of roundabouts has grown rapidly in the United States in recent years, they remain unfamiliar to many drivers. Drivers may exhibit less confidence when navigating a roundabout than they do at a traditional intersection. Clear guidance is needed at all roundabouts to make the direction of travel clear. At multilane roundabouts, drivers need guidance to identify the correct path through the roundabout to reach their desired destination. Advance-destination guide signs assist drivers in determining, prior to entering the roundabout, which lane to travel in and where to exit the roundabout, allowing them to focus more attention on the driving task and less attention on wayfinding. Drivers who have confidence in their position and path approaching, travelling through, and exiting the roundabout are less likely to perform erratic maneuvers or unexpected lane changes, which may improve safety for them and other drivers around them. To supplement advance-destination guide signs, exit guide signs are recommended to indicate the destination of each exit from the roundabout. Exit guide signs provide drivers with reassurance that they have selected their intended exit at the roundabout. Design Guidelines Advance-destination guide signs may be used on approaches to roundabouts to indicate destinations for each exit from a roundabout. There are primarily two types of advance-destinations guide signs that can be used at roundabouts: signs with text and arrows only and diagrammatic signs. Exit guide signs may be used at each departure leg of the roundabout to communicate to the driver the destination of the exit they selected. Advance-Destination Guide Signs Signs with text and arrows only: Source: MUTCD (1) Signs with text and arrows only may be appropriate at roundabouts in urban areas, on smaller roads, or at locations where space is limited (2). Curved stem arrows may be used to represent left-turn movements (2). Diagrammatic signs: Source: MUTCD (1) On larger roads and in suburban or rural areas where space is available, diagrammatic signs are preferred over signs with text and arrows only because they reinforce the form and shape of the approaching intersection and make it clear to the driver how they are expected to navigate the intersection (2). Diagrammatic signs can be particularly useful at roundabouts with atypical geometry, such as at roundabouts with skewed approaches or that have five or more legs (2). Exit guide signs: Source: MUTCD (1) Exit guide signs can be placed either on the right-hand side of the roundabout exit or in the splitter island. Where feasible, placement in the splitter island is recommended to maximize visibility of the sign (2). Based Primarily on Expert Judgment Based Equally on Expert Judgment and Empirical Data Based Primarily on Empirical Data

HFG ROUNDABOUTS VERSION 2.1 30-7 Discussion Although roundabouts have become more common in the United States, drivers are still relatively unsure about the proper way to navigate through a roundabout. This is largely because roundabouts involve high visual and perceptual demands due to the amount of information processing required (3). Drivers are presented with a relatively simple set of decisions at single-lane roundabouts—yield to driver on left, circulate to the right, decide where to exit. However, multi- lane roundabouts require additional decisions about lane selection and right-of-way allocation within the roundabout. Designers can play an important role in reducing driver workload and simplifying driver understanding at roundabouts, and signing is one of the most important tools designers can use, particularly at multilane roundabouts (4). Signs can be used in advance of a roundabout to provide drivers with information about lane selection as well as the destination of each exit, so that a driver’s attention within the roundabout can be more focused on yielding and interacting with other vehicles. Drivers’ navigation through roundabouts is aided by clear, well-maintained pavement markings that correspond to diagrammatic signs. The design and placement of signs is an important consideration when striving to simplify driver decision-making. Signs that consist of too much information or that are placed too closely together may result in driver distraction and information overload. In contrast, signs that consist of an appropriate amount of information and that are located appropriately will maximize the driver’s ability to perform navigation, guidance, and vehicle control tasks. Johnson (3) recommends staging information delivery by separating lane use information (as shown in the sign on the left) and destination information (as shown in the sign on the right). He states that smaller signs and simplified information improve messaging to the driver, even if it requires using multiple signs to convey the information. Sign that focuses only on communicating lane designation Sign that focuses only on communicating destination for each exit Source MUTCD (1) Signing needs are different for urban and rural applications, and for different categories of roundabouts, and should be assessed on a case-by-case basis. Design Issues NCHRP Report 672: Roundabouts: An Informational Guide, provides recommendations on the placement of exit and departure signs (2): For roundabouts involving the intersection of one or more numbered routes, route confirmation assemblies should be installed directly after the roundabout exit. These assemblies should be located no more than 100 ft (30 m) beyond the intersection in urban areas and 200 ft (60 m) beyond the intersection in rural areas. Where there are pedestrian crossings on the exit leg, these signs should be placed after the crosswalk. Cross References Arrow-per Lane Sign Design to Support Driver Navigation, 12-10 General Principles for Sign Legends, 18-2 Sign Design to Improve Legibility, 18-4 Driver Comprehension of Signs, 18-8 Complexity of Sign Information, 18-10 References 1. Federal Highway Administration. (2012). Manual on uniform traffic control devices for streets and highways. 2009 edition with revision numbers 1 and 2 incorporated. Washington, DC. 2. Rodegerdts, L., Bansen, J., Tiesler, C., Knudsen, J., Myers, E., Johnson, M., . . . O'Brien, A. (2010). NCHRP Report 672: Roundabouts: An Informational Guide. Second Edition. Transportation Research Board of the National Academies, Washington, DC. 3. Johnson, M. (2019). Safety Impacts of Signing and Pavement Markings on Property-Damage-Only Crashes at Multi-Lane Roundabouts. Transportation Research Record, No.2673, pp. 477-488. 4. Kinzel, C. S. (2003). Signing and pavement-marking strategies for multi-lane roundabouts: An informal investigation. Paper presented at the 2nd Urban Street Symposium, Anaheim, CA.

HFG ROUNDABOUTS VERSION 2.1 30-8 ACCOMMODATIONS FOR BICYCLISTS AT ROUNDABOUTS Introduction Intersections converted to roundabouts typically experience substantially fewer motor vehicle crashes; however, bicycle crashes can increase at roundabouts (1, 2). Vehicle-bicycle crashes generally involve a vehicle entering or exiting a roundabout where cyclists are circulating (3, 4). Often, these crashes involve a driver that looked but didn’t see the cyclist (3), so slow driving speeds and increased cyclist visibility are important for reducing crashes. While cyclists are accustomed to riding in bike lanes to the right of traffic, or on the right edge of the lane to allow vehicles to pass, this riding path may make cyclists less conspicuous to drivers entering or circling the roundabout. Research has shown that when bicycles travel in the lane with motor vehicle traffic, they are seen by drivers sooner than when they travel on the outside of the motor vehicle lanes (4). Design Guidelines COUNTERMEASURES FOR IMPROVING BICYCLIST SAFETY AT ROUNDABOUTS  A bike lane on an approaching roadway to a roundabout should not be continued through the roundabout and should allow bicyclists using the bike lane to merge into traffic through the roundabout. Bike lanes on roundabout approaches should be terminated at least 100 ft (30 m) upstream of the entrance line. Shoulders should also be terminated prior to the roundabout.  A roundabout should be designed to encourage bicyclists to ride in the center of the circulating lane with motor vehicle traffic, even if a separate bicycle path outside the roundabout is also provided. Consider using sharrows within single or multilane roundabouts to guide bicyclists’ path and inform drivers to be alert for bicyclists.  A bike lane taper should resume on the roundabout exit beyond the crosswalk. A dotted line should be used along the taper until the full bicycle width is achieved, and then a solid line should be used to separate the bike lane from the travel lane.  A separate shared use path or designated bicycle facility should be provided outside the circulating roadway when vehicle and bicycle volumes are high or where vehicle travel speeds are high. If possible, a buffer area between the circulating roadway and the bicycle or shared use path should be present.  Based Primarily on Expert Judgment Based Equally on Expert Judgment and Empirical Data Based Primarily on Empirical Data This figure illustrates the termination of a bike lane in advance of the roundabout entrance, the provision of a ramp to allow cyclists to exit the roundabout and use a shared use path to go around the roundabout, pedestrian crossings that can be used by (dismounted) cyclists, and the initiation of a bike lane at the roundabout exit, downstream from the marked crossing. Cyclists who do not choose to use the ramp to access the shared use path can proceed through the roundabout as a vehicle. This works best when roundabout design forces lower vehicle speed that is similar to bike speeds. Source: Rodegerdts et al., Exhibit 6-67 (5).

HFG ROUNDABOUTS VERSION 2.1 30-9 Discussion Jensen (1) found that bicycle crashes increased at intersections converted to roundabouts for almost all bicycle facility types. The only facility to reduce bicycle crashes after the conversion was a separated cycle path with priority giving to motorists, rather than bicycles, at the crossings on the intersection approaches. The highest increase in bicycle crashes was seen at locations with a colored bicycle lane through the roundabout. Daniels et al. (2) found that roundabouts with cycle lanes perform worse than roundabouts with mixed traffic (no bicycle facility), separate cycle paths, or grade- separated cycle paths, and that the severest bicycle crash types increased when intersections were converted to roundabouts regardless of the bicycle facility used. Cumming (3) observed 130 individual cyclists at three roundabouts in Melbourne and found that cyclist behavior was potentially contributing to crashes, as nearly two-thirds of cyclists traveled on the outside of the lane—sometimes parallel with cars, which the other third traveled more of a straight line path through the roundabout, cutting across the circulating lanes. Only five cyclists entered the lane from the middle of the lane, but even these cyclists did not stay in that position throughout the roundabout. Cumming suggests strategies that 1) encourage cyclists to start in the center of the lane and remain there through the roundabout, 2) communicate the presence of cyclists to drivers, and 3) slow motor vehicle traffic are all key to maximizing cyclist visibility and reducing crashes. The National Association of City Transportation Officials (6) suggests one strategy for encouraging bicyclists to ride in the center of the lane is to provide sharrows within single or multilane roundabouts because bicycle lanes should not be provided within the roundabout (5, 7). This strategy should be used with caution, however, as the MUTCD does not explicitly address using sharrows in roundabouts. See also Shared Use Lanes on page 29-12. Using a driving simulator, Jorgenson (4) found that driver behavior is more consistent at roundabouts without cycle facilities, and the time from when the circulating cyclist passes the conflict point at the roundabout entrance to when the vehicle entering the roundabout arrives at the conflict point is significantly less when cycle facilities are present. The study also found that drivers detected the presence of cyclists earlier where there were no cycle facilities, and that coloring the cycle lane blue or orange did not help drivers detect cyclists sooner. (4) Design Issues To better accommodate cyclists of all skill and comfort levels, designers should strive to design the roundabout for bicyclists to traverse either as a vehicle or as a pedestrian, especially where motor vehicle speeds and/or volumes are high. For bicyclists traveling as vehicles (which is best suited at locations where vehicle speeds are not substantially higher than bike speeds), bikes should be forced to mix with traffic by terminating bike lanes at least 100 ft upstream of the yield line. For bicyclists who are less comfortable traveling in the circulatory roadway, a separate bicycle track or shared use path can be provided outside the roundabout. The roundabout design can include ramps to allow cyclists to move from the bike lane or shoulder onto the shared use path. Care must be taken to prevent pedestrians with visual impairments from mistaking the bicycle ramps for a pedestrian crossing. (8) Cross References Markings for Bicycles at Intersections, 29-2 Bicycle Lanes, 29-6 Separated Bicycle Lanes, 29-8 Shared Use Lanes, 29-12 References 1. Jensen, S. U. (2013). Safety Effects of Converting Intersections to Roundabouts. Transportation Research Record: Journal of the Transportation Research Board, No. 2389, pp. 22–29. 2. Daniels, S., Brijs, T., Nuyts, E., and Wets, G. (2009). Injury crashes with bicyclists at roundabouts: Influence of some location characteristics and the design of cycle facilities. Journal of Safety Research, 40(2), pp. 141-148. 3. Cumming, B. (2012). High rate of crashes at roundabouts involving cyclists may be reduced with careful attention to conflict paths. Paper presented at the Australasian Road Safety Research Policing Education Conference, Wellington, New Zealand. 4. Jorgensen, B. l. C. L., & Transportation Research, B. (2009). Driver Behavior Toward Circulating Cyclists at Roundabouts: Vehicle Study with Concurrent Collection of Eye Movements. TRB 88th Annual Meeting Compendium of Papers, Washington, DC. 5. Rodegerdts, L., Bansen, J., Tiesler, C., Knudsen, J., Myers, E., Johnson, M., . . . O'Brien, A. (2010). NCHRP Report 672: Roundabouts: An Informational Guide. Second Edition. Transportation Research Board of the National Academies, Washington, DC. 6. National Association of City Transportation Officials. (2014). NACTO urban bikeway design guide (2nd ed.). New York, NY. 7. Federal Highway Administration. (2012). Manual on uniform traffic control devices for streets and highways. 2009 edition with revision numbers 1 and 2 incorporated. Washington, DC. 8. Jonsson, L., Hyden, C., and Svensson, A. (2007). Yielding behavior and interaction at bicycle crossings. Paper presented at the 3rd Urban Street Symposium: Uptown, Downtown, or Small Town: Designing Urban Streets That Work, Seattle, WA.

HFG ROUNDABOUTS VERSION 2.1 30-10 COUNTERMEASURES FOR IMPROVING ACCESSIBILITY FOR VISUALLY IMPAIRED PEDESTRIANS AT ROUNDABOUTS Introduction This guideline identifies countermeasures for improving accessibility for visually impaired pedestrians at roundabouts. Title II of the Americans with Disabilities Act (ADA) requires that new and altered public facilities be designed to be readily accessible to and usable by people with disabilities (28 CFR 35.151). FHWA states that “a visually impaired pedestrian with good travel skills must be able to arrive at an unfamiliar intersection and cross it with pre-existing skills and without special, intersection-specific training” (1). Visually impaired pedestrians typically wait much longer to cross at roundabouts than sighted pedestrians, especially if traffic volume is high. Sighted pedestrians have shorter wait times because they can accept gaps that are initially too short but use eye gazes and manual gestures to communicate with drivers to extend the gap by yielding. Because visually impaired pedestrians cannot communicate in this manner, they are forced to wait for what they deem to be sufficient gaps based on sound information. Visually impaired pedestrians rely heavily on sound cues to get a sense of what vehicles are doing, which is difficult at roundabouts due to the continuous traffic flow within the circle. Design Guidelines COUNTERMEASURES FOR IMPROVING ACCESSIBILITY FOR VISUALLY IMPAIRED PEDESTRIANS AT ROUNDABOUTS Countermeasure Description Landscaping  Providing landscaping or a planting strip between the sidewalk and the curb can help visually impaired pedestrians orient themselves and find the crosswalk more easily (1, 2, 3, 4).  Landscaping on splitter islands can provide sound separation and help visually impaired pedestrians discriminate between traffic coming toward and traffic going away from them (2,4). Pedestrian-actuated signals with accessible pedestrian signals (APS)  Sound cues can be particularly difficult to decipher at multilane roundabouts where it is difficult to distinguish a circulating vehicle from a vehicle exiting the roundabout (1). Provision of pedestrian-actuated signals with APS can provide information about the signal phase and anticipated traffic patterns to pedestrians with visual impairment. Accessible pedestrian signal pushbutton and locator tone  Provision of a pushbutton locator tone can help visually impaired pedestrians locate the pushbutton for an accessible pedestrian signal (2, 3, 4).  Placement of the accessible pedestrian signal pushbutton and locator tone immediately beside the curb ramp leading to the crosswalk provides an audible cue to the presence and location of a crosswalk (2, 4). Curb ramps and splitter island walkways— alignment and detectable warnings  Sidewalk curb ramps and splitter island cut-through walkways should be aligned with the crosswalk to help visually impaired pedestrians align themselves with the crosswalk (1, 2, 4).  Detectable warnings on curb ramps and splitter islands also help visually impaired pedestrians align themselves with the crosswalk (1, 2, 4). Based Primarily on Expert Judgment Based Equally on Expert Judgment and Empirical Data Based Primarily on Empirical Data

HFG ROUNDABOUTS VERSION 2.1 30-11 Discussion Landscaping: NCHRP Report 674 (2) and its related Guidebook in NCHRP Report 834 (4) recommend the provision of planting strips along the sidewalk. Landscaping that separates the sidewalk from the curb can help visually impaired pedestrians orient themselves and find the crosswalk more easily. It also serves as a barrier that discourages pedestrians from entering the roadway at places other than the crosswalk and makes it less likely that a visually impaired pedestrian will inadvertently step from the sidewalk into the paved roadway at any point other than at the crosswalk (or begin to cross from the wrong point without realizing the intersection is a roundabout). Planting strips also provide a trailing surface that long cane users can use to locate the crosswalk. Visually impaired pedestrians rely heavily on sound cues to determine an appropriate gap in traffic, and it is especially difficult at roundabouts to discern between vehicles coming toward them from vehicles going away from them (2,4). Visually impaired pedestrians have indicated that the provision of landscaping on the splitter island can block some of the sound from the lane behind them when they are crossing from the island to the curb. The landscaping helps with sound separation and discrimination of the traffic coming toward them from the traffic going away from them. Pedestrian-actuated signals with APS (2, 4): The crossing task for visually impaired pedestrians at roundabouts involves identifying an appropriate gap in traffic in an environment of primarily uninterrupted traffic. This task of discerning gaps in traffic is largely alleviated by the provision of pedestrian-actuated signals with APS. An APS-equipped signal can be effective at stopping traffic and at providing visually impaired pedestrians with auditory cues of when the crossing phase is active. APS installations typically include a pushbutton locator tone to help pedestrians find the pedestrian pushbutton, and an audible signal or message that alerts pedestrians when the walk phase is shown on the pedestrian signal display. Accessible pedestrian signal pushbutton and locator tone (2, 4): The task of locating a crosswalk at a roundabout is challenging for visually impaired pedestrians because crosswalks at roundabouts are not located at corners, like they are at a conventional intersection. At a crossing equipped with an APS signal, placement of the pushbutton with its pushbutton locator tone immediately beside the curb ramp leading to the crosswalk provides an audible cue to the presence and location of the crosswalk. Curb ramps and splitter island walkways—alignment and detectable warnings (2, 4): The task of properly aligning oneself to cross the roadway is challenging for visually impaired pedestrians, but can be made easier with the presence of alignment cues and detectable warnings. One alignment cue is to align sidewalk curb ramps and splitter island walkways with the crosswalk. Another alignment cue is to install a hard-curbed edge on each side of a curb ramp, in line with the direction of travel on the crosswalk. Detectable warnings, such as directional tactile surface lines, that are accessed by foot and that can be installed along with other detectable warnings, can also help visually impaired pedestrians align themselves with the crosswalk. Another potentially effective treatment, which could help with the task of maintaining alignment during the crossing, is to provide an auditory signal from the far side of the crosswalk (2, 3, 4). Design Issues Landscaping, either between the curb and the sidewalk or on the splitter island, should not block the view of pedestrians or the crosswalk for drivers. Cross References Countermeasures for Improving Accessibility for Vision-Impaired Pedestrians at Signalized Intersections, 11-8 References 1. FHWA (2000). Roundabouts: An Informational Guide (Publication FHWA-RD-00-067). Washington, DC. 2. Schroeder, B., Hughes, R., Rouphail, N. Cunningham, C., Salamati, K., Long, R., Guth, D., Emerson, R. W., Kim, D., Barlow, J., Bentzen, B. L., Rodegerdts, L., and Myers, E. (2011). NCHRP Report 674: Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities. Transportation Research Board. Washington, DC. 3. Federal Highway Administration. (2015). Accelerating Roundabout Implementation in the United States—Volume 1: Evaluation of Rectangular Rapid Flashing Beacon (RRFB) at Multilane Roundabouts. U.S. Department of Transportation. Publication FHWA-SA-15-069. Washington, DC. 4. Schroeder, B., Rodegerdts, L., Jenior, P. Myers, E., Cunningham, C., Salamati, K., Searcy, S., O’Brien, S., Barlow, J., and Bentzen, B. L. (2016). NCHRP Report 834: Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities: A Guidebook. Transportation Research Board, Washington, DC.

HFG ROUNDABOUTS VERSION 2.1 30-12 ROUNDABOUT LIGHTING Introduction In order to safety navigate a roundabout, a driver must be able to clearly see the roundabout’s layout and understand it’s operations in sufficient time to make appropriate maneuvers, including yielding to pedestrians and accommodating cyclists. Lighting is used both to enhance the visibility of the roundabout from a distance and to improve the perception of the layout and visibility of other users for the driver during hours of low light and darkness. Lighting is recommended for use at every roundabout (1). Agencies must determine how to provide cost-efficient lighting scenarios in order to light as many of their roundabouts as feasible. As with other intersection types, it can be costly to provide a power source in rural areas. Ecoluminance is a lighting technique that integrates lighting and vegetation to provide additional visual guidance at roadway features including roundabouts (3). It generally uses lights mounted on bollards (posts typically approximately three to four feet tall) for pedestrian crossings, overhead LED lamps, retroreflective elements, and a central island with landscape lighting and vegetation that can reflect light. It can also be designed to provide additional visibility to roundabout features by using foliage to reflect light emitted from car headlamps, even in the absence of additional lighting. Ecoluminance has the potential to improve visibility while reducing long-term energy costs. Design Guidelines  Wherever feasible, roundabouts should be lighted. Partial lighting is preferred to no lighting (2).  Exit and entry points, raised channelization or curbing, pedestrian crossings, and bicycle merge points should be clearly visible at night. (1)  If the surrounding area and intersection approaches are not lit, transition lighting should be provided in advance of the first trajectory change and beyond the final trajectory change to allow driver’s eyes to adjust from dark to lit conditions and then back from lit to dark conditions. (1)  Vegetation can be used to help reflect light from vehicle headlamps and/or low-height lighting fixtures to make the central island, the roundabout geometry, and crossing pedestrians more visible to motorists even when full lighting is not feasible. This is referred to as ecoluminance. (3, 4)  Pedestrian crossings should be lit from the front (rather than from directly overhead) to increase positive contrast for pedestrians against a darker background. Bollards with a light can be used near crosswalk endpoints and in crossing islands to directly light crossing pedestrians. (1, 4, 5) Renderings of Lighting Strategies at Roundabouts. The image on the left illustrates using approach lighting to highlight pedestrian crossing (5). The image on the right illustrates using low-level light reflected off of foliage in the central island to highlight roadway geometry and pedestrian-height bollards to light pedestrian crossings (4). Center island presence and luminance are improved when retroreflective signs are used. Based Primarily on Expert Judgment Based Equally on Expert Judgment and Empirical Data Based Primarily on Empirical Data

HFG ROUNDABOUTS VERSION 2.1 30-13 Discussion Lighting of roundabouts is important because headlights alone often cannot provide adequate illumination of the roundabout path due to the tight radius of the roundabout. When full lighting can be provided, the Illuminating Engineering Society’s “Design Guide for Roundabout Lighting” (now part of “American National Standard Practice for Design and Maintenance of Roadways and Parking Facility Lighting”) is considered the primary source for lighting design guidance (6). However, Rodgers et al. found that 68 to 83 percent of the benefits of full illumination at a roundabout could be achieved with partial illumination. (5) When partial illumination is provided, the focus should be on lighting pedestrian crossings using either approach lighting in advance of the crosswalk or bollards with lights near the crosswalk in order to illuminate pedestrians from the front (rather than from directly above or behind) and on making the geometry of the roundabout clear to drivers. Ecoluminance is a strategy that can be employed to use vegetation to reflect light to highlight roadway geometry (3, 4). Headlights alone often cannot provide good illumination of the roundabout path due to the tight radius of the roundabout. Design Issues It can often be difficult to bring a power source to rural roundabouts in order to provide traditional lighting fixtures. Nevertheless, while lighting is recommended at all roundabouts, it is especially critical at locations where pedestrians are expected and where traffic speeds are high, requiring more time to perceive and react to changes in roadway geometry. Lighting fixtures should be as far from the curb as possible and should avoid locations where run-off-the-road crashes are more likely. (1, 4) Mowing and plowing operations should be considered when placing bollard-style fixtures and other low-level lighting fixtures. Ensure lighting fixtures are not placed where snow is expected to be deposited and stored in the winter. (3) Cross References Countermeasures for Improving Pedestrian Conspicuity at Crosswalks, 21-8 Characteristics of Lighting that Enhance Pedestrian Visibility, 21-10 Characteristics of Effective Lighting at Intersections, 21-12 References 1. Rodegerdts, L., Bansen, J., Tiesler, C., Knudsen, J., Myers, E., Johnson, M., . . . O'Brien, A. (2010). NCHRP Report 672: Roundabouts: An Informational Guide. Second Edition. Transportation Research Board of the National Academies, Washington, DC. 2. Rodgers, M. O., Hunter, M., Samoylov, A., Gbologah, F., and Berrebi, S. J. (2016). Evaluation of current practice for illumination at roundabouts: Safety and illumination of roundabouts (Phase I). Forest Park, GA: Georgia Department of Transportation. 3. Bullough, J. D. (2013). Ecoluminance: A new approach to visual guidance for roadways. International Journal of Sustainable Transportation, 8(2), pp. 127-150. 4. CTC & Associates. (2014) New approaches for roundabout lighting to enhance pedestrian safety. Transportation Research Synthesis 1413 (20p): Local Road Research Board, Minnesota Department of Transportation Research Services and Library. 5. Lutkevich, P., and Hasson, P. (2005) An Examination and Recommendation for Current Practices in Roundabout Lighting. In Transportation Research Circular E-C083: National Roundabout Conference. Transportation Research Board of the National Academies, Washington, DC. 6. Illuminating Engineering Society. American National Standard Practice for Design and Maintenance of Roadway and Parking Facility Lighting. ANSI/IES Standard RP-8-18. Illuminating Engineering Society of North American, New York,

Next: Chapter 31: Additional References »
Human Factors Guidelines for Road Systems 2021 Update, Volume 1: Updated and New Chapters Get This Book
×
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

In 2015, there were more than 6 million police-reported crashes in the United States. While crashes are complex and it is generally interactions between road users, vehicles, and the environment that lead to crashes, some form of driver error is a contributing factor in most crashes.

The TRB National Cooperative Highway Research Program's NCHRP Web-Only Document 316: Human Factors Guidelines for Road Systems 2021 Update, Volume 1: Updated and New Chapters is an addendum to NCHRP Report 600: Human Factors Guidelines for Road Systems (HFG),Second Edition, which was the first complete holistic release of the HFG.

Supplemental to the document is a flier describing the updated and new chapters and NCHRP Web-Only Document 316: Human Factors Guidelines for Road Systems 2021 Update,Volume 2: Conduct of Research Report.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  6. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  7. ×

    View our suggested citation for this chapter.

    « Back Next »
  8. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!