Research and Resources


Empirical research about the accessibility of modern roundabouts is in its infancy. In 1999, a program of research on roundabout accessibility was initiated by Western Michigan University and Vanderbilt University. Conducted at three modern roundabouts in metropolitan BaltimoreMaryland, the study provides information about the ability to use vision and hearing to distinguish ‘crossable’ gaps in traffic from gaps that are too short to afford safe crossing. ‘Crossable gaps’ were defined as those that would have allowed pedestrians sufficient time to cross from a curb to a splitter island before the arrival of the next vehicle at the crosswalk. The results of the study suggest that there are significant differences in the ability of blind and sighted pedestrians to determine whether it is safe to initiate a crossing at some roundabouts, presumably because of differences in the way information is obtained to make decisions about crossings.

The Western Michigan/Vanderbilt team also conducted a comparable study at three roundabouts in the greater Tampa, Florida area with similar results.  A principal finding of this research was that the ability to judge whether gaps are crossable or not is strongly affected by vehicle volume.  For example, the judgements of blind and sighted pedestrians were similar at a single-lane roundabout at mid-day, but blind pedestrians were significantly disadvantaged at rush hour.  

The team is currently studying the behavior of blind and sighted pedestrians as they cross at roundabouts and the behavior of drivers as they approach blind pedestrians waiting at uncontrolled crosswalks (both at roundabouts and mid-block crosswalks). Preliminary analysis suggests that few drivers yield, although this varies widely from crosswalk to crosswalk. While such research has begun to address several of the key issues cited earlier in this bulletin, it is clear that much more work remains to be done.

Improvements for gap identification/notification

  • ITS technologies with APS or other audible output
  • sound surfaces on entrance/exit legs

Note: avoid masking vehicle sounds with water features in central island or nearby



The dearth of research addressing the negotiation of roundabouts by blind pedestrians has prompted Federal funding of several projects on this topic. The first, funded by the National Eye Institute of the National Institutes of Health, was awarded in 2000 to a consortium led by Western Michigan University. This project emphasizes the identification of variables affecting blind pedestrians’ safety while crossing streets at roundabouts and treatments to enhance this safety. The second project, funded by the National Institute on Disability and Rehabilitation Research, was awarded in 2001 to a consortium led by the Sendero Group, LLC. This project emphasizes the identification of wayfinding information needed by blind pedestrians at roundabouts (e.g., crosswalk location, intersection geometry) and ways to convey this information to the pedestrian. A third project, focused specifically on the usability of roundabouts and slip lanes by pedestrians who have vision impairments, will be awarded in 2004 by the National Cooperative Highway Research Program (a prior NCHRP study still underway will identify "geometric, traffic, and other characteristics that are expected to affect the safety and operation of all roundabout users, including bicycles, pedestrians, and pedestrians with disabilities" and to "refine geometric and traffic control design criteria used for roundabouts, including….treatments for bicycles and pedestrians (including pedestrians with disabilities and including the impact of accessible pedestrian signals on pedestrian access and vehicle operations)…"). The Turner-Fairbanks Research Center of the Federal Highway Administration/DOT has a human factors study newly underway that will test several potential improvements to roundabout usability by pedestrians who have vision impairments.

Collectively, these and other projects should significantly enhance engineers’ and planners’ access to information about how to build roundabouts that can be negotiated safely and efficiently by blind pedestrians.


The U.S. Access Board is an independent Federal agency that develops accessibility guidelines for buildings, facilities, transportation vehicles, and communications technologies and electronic devices covered by the ADA and other laws. In 1999, the Board established a Public Rights-of-Way Access Advisory Committee (PROWAAC) to make recommendations on accessibility guidelines for public rights-of-way. The 33 members of PROWAAC represented Federal agencies, traffic engineering organizations, public works agencies, transportation departments, traffic consultants, standard-setting organizations, disability organizations, and others. On January 10, 2001, the PROWAAC submitted its report to the Board recommending a new national set of guidelines for accessible sidewalks, street crossings, and related pedestrian facilities. The report includes several recommendations regarding access to roundabouts. In particular, the report recommends:

  • barriers (landscaping, railings, bollards with chains) where pedestrian crossings are prohibited;
  • cues (locator tones, detectable warnings, other) to identify crossing locations; and
  • pedestrian-activated traffic signals at crossings.

The Access Board will consider Committee recommendations in developing a Notice of Proposed Rulemaking (NPRM) on guidelines for public rights-of-way for publication in the Federal Register. The NPRM will seek public input and comment on the proposed guidelines before a rule is finalized. Further information on the status of this rulemaking is provided on this website.


Additional resources on public rights-of-way accessibility available from the Board include:

Building a True Community, a report from the Public Rights-of-Way Access Advisory Committee submitted to the Board in January 2001.

Accessible Rights-of-Way: A Design Guide, a guide the Board developed in cooperation with the Federal Highway Administration to provide advisory information until guidelines for public rights-of-way are developed (also available in PDF format).

Accessible Pedestrian Signals, a Board report that provides a synthesis on current technology in accessible pedestrian signals, including a listing of devices and manufacturers in the U.S. and abroad, and a matrix comparing the features of each device. (Also available in  PDF format). Note: A more recent synthesis of accessible pedestrian signal technologies developed through the National Cooperative Highway Research Program (NCHRP) is avaialble at

Detectable Warnings: Synthesis of U.S. and International Practice, a Board-sponsored study on detectable warnings that surveys the state-of-the-art in the U.S. and abroad and summarizes the installation and effectiveness of various designs. (Also available in PDFformat).

Resources available from the Federal Highway Administration include:

Roundabouts: An Informational Guide, a comprehensive overview of roundabouts.

Manual of Uniform Traffic Control Devices, which contains standards for the application and installation of traffic signals, signs and pavement markings that regulate, warn, and guide the vehicle and pedestrian users of the public right of way. The MUTCD promotes the uniformity of traffic control devices nationwide.

A summary of roundabouts research concerning access by individuals who are blind is also available:

Non-visual gap detection at roundabouts by pedestrians who are blind: A summary of the Baltimore roundabouts study  

David Guth, Richard Long, Paul Ponchillia
Western Michigan University

Dan Ashmead, Robert Wall
Vanderbilt University

 Support for this work was provided by the US Access Board, the National Eye Institute of the National Institutes of Health, and the the American Council of the Blind

This report is a summary of a research project conducted in the Baltimore, Maryland metropolitan area in April, 2000. The study was the first of a series of research projects to be conducted to evaluate access to modern roundabouts by pedestrians who are blind. The long-term goals of the research program are to determine where interventions may be needed at roundabouts to facilitate safe and efficient street crossings, to identify potential interventions, and to evaluate the effectiveness of these interventions.

The Americans with Disabilities act and its implementing regulations require that public rights-of-way be accessible to all users, including pedestrians with disabilities. Some roundabouts may pose barriers to safe and efficient independent travel by some individuals with blindness and low vision. The research described in this report provides information about the ability of blind pedestrians to use their hearing to distinguish "crossable" gaps in traffic at roundabouts from gaps that are too short to afford safe crossing. "Crossable gaps" were defined as those that would have allowed pedestrians sufficient time to cross from a curb line to a splitter island before the arrival of the next vehicle at the crosswalk.

The study was conducted at three modern roundabouts in metropolitan Baltimore, MD with assistance from the Maryland Department of Transportation. The three roundabouts included a large, high-volume, urban, two-lane roundabout (the Towson Roundabout); an intermediate volume, urban, two-lane roundabout (the Annapolis Gateway Roundabout); and a low-volume, single-lane roundabout (the University of Maryland – Baltimore County Roundabout, "UMBC").


Six blind individuals and four sighted individuals participated in the study. All participants routinely traveled in urban areas; most were familiar with roundabouts; and all were familiarized with each roundabout before making their judgments. Participants stood at roundabout crosswalks and observed traffic continuously during 2-minute periods. Whenever they believed they could complete a crossing before the arrival of the next vehicle at the crosswalk, they pressed a button, and button presses were recorded on a laptop computer. The criterion used to judge whether a gap was acceptable or not was a conservative one that does not rest on the assumption that all approaching vehicles would yield. In addition to the buttons used by participants (typically, an individual who was blind and an individual with typical vision participated at the same time), a third sighted observer used a button to record the arrival of vehicles at the crosswalk. This made it possible to measure the durations of the gaps that occurred at the crosswalk during each 2-minute trial as well as to relate participants’ judgments of appropriate times to cross to the arrival of vehicles at the crosswalk. Participants completed at least six, two-minute trials at an entry and an exit leg of each of the three roundabouts.

The average duration of the gaps between vehicles was 5 seconds at Towson, 7 seconds at Annapolis, and 20 seconds at UMBC. At both Annapolis and Towson, most gaps were so brief that pedestrians walking at 4 feet per second would not have been able to fully cross before the next vehicle arrived at the crosswalk. At UMBC, it was very common to have gaps longer than 10 seconds, and there were frequent periods of "all quiet." Listening for such periods appeared to be an effective strategy for identifying acceptable gaps at UMBC, where blind and sighted participants rarely indicated that it was appropriate to cross when there was not enough time to reach the splitter island before the arrival of the next vehicle. However, it was rarely "all quiet" at Annapolis or Towson, thus requiring participants to judge when vehicles that they could hear and/or see would arrive at the crosswalk. A vehicle traveling at 20 miles per hour travels 29.3 feet per second. Pedestrians typically need at least 5 seconds to cross to or from a splitter island, so to be entirely safe, a pedestrian needs to know about vehicles that are about 150 feet away.


A "risky" crossing judgment was defined as one for which there would not have been sufficient time to reach the splitter island before the arrival of the next vehicle. By this definition, "risky" crossings would require either that all vehicles yield to pedestrians who were crossing the street and/or that the pedestrian were able to monitor the speed and trajectory of nearby vehicles and take evasive action as necessary. A "safe" judgment was one in which there would have been sufficient time to reach the splitter island.


At UMBC, "risky" judgments were few and not significantly different across the two groups. At Towson and Annapolis, however, blind participants averaged more than twice as many "risky" judgments as sighted participants. Thus the degree of risk would have been much greater for the blind participants than the sighted participants had they actually initiated a crossing at the time they indicated that it was appropriate to do so. That is, the blind participants were much more likely than the sighted participants to indicate that there was an acceptable gap when approaching vehicles were only 2 or 3 seconds away. Towson’s exit lanes stood out as particularly problematic for blind participants, with 70% of the judgments falling in the "risky" category. Participants reported having difficulty in this condition due to a combination of the high level of traffic noise at this roundabout and the need to monitor both (a) vehicles on adjacent legs that could quickly reach the exit lane crosswalk and (b) vehicles on the circulatory roadway that might or might not exit.


In addition to investigating the accuracy of participants’ judgments about whether gaps were acceptable or not, the research team also investigated differences in the latency of these judgments. Considering only the acceptable gaps that were correctly detected, blind participants made their judgments approximately 3 seconds later than sighted participants. This finding was consistent at all three roundabouts. This appears to be because vehicles that have just cleared the crosswalk produce engine and tire noise that masks other sounds, interfering with blind pedestrians’ ability to hear whether or not there is another the vehicle approaching the crosswalk. Sighted pedestrians can typically identify the onset of an acceptable gap just as a vehicle clears the crosswalk, but blind pedestrians must let the vehicle pass and wait several seconds for its sound to recede into the distance so that any approaching traffic can be heard

A three-second delay in detecting an acceptable gap probably is of little consequence at low volume, long-gap roundabouts such as UMBC. However, a delay of three seconds would appear to be important at higher volume roundabouts, considering that many of the gaps at such roundabouts may be just long enough to afford safe crossing. At the two higher volume roundabouts studied, delays of three seconds resulted in the inability of blind pedestrians to detect many of the acceptable gaps, or resulted in the detection of gaps too late to make a safe crossing.


These data indicate that there are significant differences in pedestrians’ abilities to determine whether it is safe to initiate a crossing at some roundabouts, depending on whether they are using vision and hearing or hearing alone. These differences have important practical implications for traffic engineers who wish to design roundabouts that are accessible by blind users and to blindness researchers and O&M instructors who wish to find ways to reduce these differences through training.

More work is needed to build upon these early data. Existing pedestrian signals now in place should be analyzed for cost, usability, and accessibility. Additional specialized research and development is necessary to investigate ways of providing useful auditory and tactile cues to roundabout use that can be pilot-tested at roundabouts now in planning or under construction. New roundabouts research should routinely include pedestrian and accessibility considerations in addition to vehicle studies.