1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
ROUNDABOUTS AND THE ACCOMODATION OF LARGE TRUCKS: A MOTOR CARRIER
PERSPECTIVE
TRB 2013 Annual Meeting
Word Count: 3,777 Text + 500 Figures = 4,277 Total
Submitted July 31, 2012
Lisa Park (Corresponding Author)
Research Analyst
American Transportation Research Institute
2060 Franklin Way, SE Suite 201
Marietta, GA 30067
(770) 432-0628
Phone: 770-432-0628 x.3
Fax: 770-432-0639
Email: [email protected]
David Pierce
Research Associate
American Transportation Research Institute
2060 Franklin Way, SE Suite 201
Marietta, GA 30067
Phone: 770-432-0628 x.4
Fax: 770-432-0639
Email: [email protected]
Paper revised from original submittal.
Park and Pierce
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
1
ABSTRACT
With nearly 200 new constructions every year, roundabouts are increasingly utilized as alternatives for
signalized and stop-controlled intersections in the United States. Proponents often cite numerous safety
improvements, including reductions of overall crash rates at converted intersections, as justification to
increase the development of roundabouts. However, the growing use of roundabouts may be inhibiting
the safe and efficient movement of large trucks due to roundabout design elements that conflict with truck
operations. ATRI researchers, collaborating with Kansas State University, conducted an online survey of
motor carriers to explore features that may possibly hinder roundabout use by large trucks. The survey
collected industry observations regarding the challenges experienced by commercial truck drivers while
negotiating roundabouts. This paper synthesizes those observations and documents the anecdotal
experiences that will allow researchers and roadway designers to identify and categorize unknown
roundabout design issues and possible solutions. This research can hopefully be used as the first
conversation in a productive dialogue between transportation planners and the trucking industry on the
issue of roundabout design for large truck usage.
TRB 2013 Annual Meeting
Paper revised from original submittal.
Park and Pierce
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
2
INTRODUCTION
Roundabouts can offer several advantages over signalized and stop sign controlled intersections,
including better overall safety performance, increased traffic capacity, and improved traffic flow. (1) The
effectiveness of roundabouts, however, may be greatly diminished due to a potential inability to
accommodate large trucks. Numerous motor carriers have identified roadway roundabouts as roadway
design features creating safety issues for large trucks. To understand further the impact that roundabouts
have on trucking operations ATRI, in coordination with Kansas State University (KSU), sought industry
feedback on how to accommodate large trucks without sacrificing the safety and operational efficiency of
the roundabout.
The purpose of this paper is to synthesize trucking industry observations regarding the challenges
experienced by commercial truck drivers while negotiating roundabouts. Documenting the anecdotal
experiences and the nature of these conflicts may allow researchers and roadway designers to identify and
categorize unknown roundabout design issues and possible solutions. This research can then be used as
the first conversation in a productive dialogue between transportation planners and the trucking industry
on the issue of roundabout design for large truck usage.
LITERATURE REVIEW
A large body of research exists that addresses various safety aspects, design features and environmental
considerations of roundabouts. Past research has used numerous methodologies to observe the effects of
roundabout implementation on safety and traffic patterns. While roundabouts have safety benefits for the
general traveling public, there is a shortage of literature focusing on the accommodation of less common
vehicle configurations in roundabout design, particularly large trucks. A roundabout is a one-way circular
intersection smaller than a high-speed rotary but larger than neighborhood traffic circles. Often referred
to as “traffic calming” devices, roundabouts are designed to eliminate conflicting traffic and slow driving
speed using mechanisms such as right-turn-only entries and exits, counterclockwise flow, and curved road
geometry. Roundabouts are considered to be cost-effective safety and aesthetic intersection
improvements. The Federal Highway Administration recommends building approximately 1,000 welldesigned roundabouts per year to reduce crashes and improve intersection safety. (1)
Even with research documenting the safety benefits of roundabouts, a number of crashes still
occur. These crashes are typically more prevalent at multi-lane roundabouts compared to single-lane
roundabouts. (2) Roundabout crashes typically fall into four classes: run-off-road, rear-end, sideswipe,
and entering-circulating. (3) Contributing crash factors at roundabouts include driver sight distance,
failure to yield to vehicles in the circulating lane, and high speed differentials. (2,3)
Large trucks are of particular concern when considering roundabout navigation. The roundabout
problem for large trucks is often not reflected in accident statistics, as roundabout accident severity is
typically low. Roundabout accident statistics tend to spotlight reductions of injuries and fatalities and
discuss less often cases where there is property damage only (PDO). PDO large truck roundabout
accidents typically involve no other vehicle, occur at low speed and often do not result in injuries. (4)
Nevertheless, they have economic consequences due to road damage, truck damage and subsequent traffic
jams. Research has shown that average PDO crashes range in cost from $100,150 to $196,958, depending
on the type of crash. (5)
Roundabouts should be designed considering the need to accommodate the largest vehicle likely
to use the intersection. (6) Design features used to make roundabouts traversable for larger vehicles
include placing a mountable apron around the center island, making center islands fully traversable, and
the use of gated pass-throughs. These design features, however, can often comprise safety at the
roundabout by reducing deflection, which is needed to slow passenger vehicle and often involve tradeoffs
in total capacity and costs. Introduction of a truck apron (an area between the circular roadway and the
central island not designed for smaller vehicle use) is a possible solution, but even this can lead to further
problems, such as load shifting on trucks, which can lead to rollovers even at low speeds. (7)
TRB 2013 Annual Meeting
Paper revised from original submittal.
Park and Pierce
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
3
Roundabouts are relatively new to the United States; therefore, a small amount of literature
regarding the use of roundabouts by large trucks exists. However, this literature does document several
roundabout design features created to accommodate large trucks. Even with these design features, trucks
still have difficulty navigating some roundabouts as these design features are not always properly
developed. Little information exists on common problems that large trucks encounter when navigating a
roundabout.
METHODOLOGY
Roundabouts are becoming increasing popular in the Nation’s transportation system; however, the impact
these features have on truck mobility has not been fully addressed. Even when truck-accommodating
features are in place, a lack of standard design guidelines leads to unexpected truck accidents such as
rollovers and undercarriage damage. Given that communication between roundabout designers and the
truck drivers who use them rarely occurs, the ATRI Research Team has conducted research to collect
industry observations regarding the challenges experienced by commercial truck drivers negotiating
roundabouts. In an effort to synthesize this commentary, the ATRI research team conducted a survey of
60 carriers from various industry sectors. To reach this population, ATRI researchers collaborated with
KSU to develop and host an online roundabout survey.
Online surveys were chosen as an appropriate and economical method of gathering data given the
geographic extent of the carrier population. The online format also supported the use of open–ended
questions. Researchers felt the format allowed survey participants to set aside time to carefully
contemplate the questions and their responses. To reach a large number of participants, the survey was
advertised in several industry newsletters and on industry stakeholder websites.
The survey consisted of 47 questions related to demographics, observations from anecdotal
roundabout use, and possible solutions/alternatives to known design issues. The questions were a mix of
closed-ended and open-ended questions to generate both quantitative and qualitative data. Since the
survey was focused on generating the most feedback possible, many closed-ended questions were
accompanied by comment boxes allowing participants to include extra remarks. The first portion of the
survey, 30 questions, related to trucks of all configurations, while the latter part of the survey focused on
the use of roundabouts by oversize-overweight trucks (OSOW).
Researchers at KSU analyzed the survey in its entirety, focusing primarily on the use of
roundabouts by OSOW commercial vehicles. Given that OSOW vehicles constitute less than three
percent of all trucks operating in the U.S. (8), the ATRI Research Team has produced a separate analysis.
This paper will analyze the carrier responses specifically from the first portion of the survey for those
carriers who indicated having 5-axle tractor/semi-trailer combinations in their fleet. This type of truck
configuration represents about 26 percent of the national truck fleet and more than 82 percent of all
combination trucks. (8)
ANALYSIS
Industry Demographics
Of the 60 surveys completed, the majority of respondents (52) indicated using 5-axle
tractor/semi-trailer configurations in their fleet and the population skewed towards the for-hire sector. Of
those carriers, 81 percent operated in the for-hire sector and the remaining 19 percent operated as a
private fleet. This distribution differs from the American Trucking Association’s annual American
Trucking Trends report which indicates that most of all U.S. motor carriers operated as a private fleet
(53.1%) followed by the for-hire sector (33.2%) and “other” (13.6%) in 2011. (9) The sample bias
towards for-hire carriers should not significantly bias the results, as there is little to no difference between
how a for-hire versus private truck navigates a roundabout.
Within both sectors surveyed, truckload carrier (39%) was the most frequent response. Other
carriers identified themselves as flatbed (17%), less-than-truckload (14%), private fleet/shipper (12%),
TRB 2013 Annual Meeting
Paper revised from original submittal.
Park and Pierce
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
4
tanker (9.5%) and other (9.5%). Figure 1 displays the number of carriers who identified with each carrier
type. Nationally, the distribution of for-hire carriers is 52 percent truckload, 24 percent less than
truckload and 24 percent specialized. (10)
Respondents were then asked to identify the primary road types on which their trucks typically
travel and could choose all that apply. The most frequent selection, rural interstates, highways and
freeways, were chosen by 88 percent of the respondents followed by urban interstates, highways and
freeways (84%), urban major highways (69%), urban local roads (69%), rural major highways (73%) and
rural local roads (67%).
Roundabout Concerns
After questions aimed at gathering the respondent population demographics; the survey continued
with a series of questions about the use of roundabouts by commercial trucks to gauge their opinions
about some of the known issues with roundabouts. Participants were asked if roundabouts are any more
of a problem compared with other intersections and, separately, if roundabouts are any more of a problem
than other highway features such as narrow bridges, wires, curbs, and ramps. Nearly two-thirds (73%)
believed that roundabouts were more of a problem compared to other intersections and slightly less (69%)
responded that roundabouts are more of a problem than other concerning features. Sixty-two percent of
respondents cited unique problems with roundabouts; some of the most common responses included the
following themes:
 Roundabouts are too small to accommodate large trucks
 Trailer encroaches onto center of roundabout
 Trailers drift into the second lane causing the potential for a collision
 Large trucks are unable to make the turn without running on curbs
 Difficulty accelerating quickly enough to merge into traffic
 Drivers of passenger vehicles are not educated enough – do not know to give the tractor/trailer the
necessary room to maneuver and do not yield to signs indicating trucks need both lanes
 Create blind-spot on right side of tractor-trailer
 Elevated and sloped curbs cause trailers to hang up on any turns more than 90 degrees
 Not well documented for routing purposes and cause unnecessary out of route costs to shippers
As an open-ended follow-up question, respondents were asked for possible solutions to the
problems they presented. These ideas were solutions they thought could mitigate the problem without
compromising a roundabout’s safety benefits to passenger vehicles, or requiring excessive right of way
and cost. The submitted concepts related to better geometric design, improved signage, education
outreach and advanced planning. Specific resolutions included the following:
 “Keep designs free of shrubs, curbs, rocks and signs, and anything that hinders the use of
lowboys and other specialized equipment that is currently used to move today's O D cargoes.”
 “All roundabouts proposed/constructed on roads that permit large trucks must be engineered and
constructed so as to be of a size that allows large trucks to fully utilize the circulating roadway
without riding the trailer tires over the curb/apron of the roundabout island. At a minimum, these
roundabouts must be of a size designed to fully accommodate the off-tracking of large truck
pulling a 53' trailer that has its tandem wheels in the rearmost position.”
 “Increase the diameter of the roundabouts. Add directional signs well ahead of the roundabout.
Improve public knowledge of the laws pertaining to roundabouts.”
 “It is necessary for all areas to have a designated truck route. All truck routes should be free of
this type of issue. It is unfair to put the burden of liability and safety on the truck
driver/owner/operator for damages and the safety of passenger cars when they have no other
option. We all have to compromise but why does it always have to be the truck driver that has to
figure out a way around the problem?”
TRB 2013 Annual Meeting
Paper revised from original submittal.
Park and Pierce
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21

5
“Do not build them on Interstate or State Highways, or intersections that connect said highways.
Do not build a roundabout anywhere before the state, city and county governments has looked at
their long term planning for regional projects both public and private. Do not put a cork in the
bottle you want to build a ship in!”
When considering three specific roundabout maneuvers, respondents were asked to rate the
degree to which each maneuver was hindered. For the approach, the circular roadway, and the departure,
participants rated the maneuver as one where either a serious problem exists, a problem exists but is not
so serious, or there is no problem. Table 1 displays the distribution of rankings for each maneuver. The
circular roadway was most often a serious problem opposed to the departure where a problem exists but is
not so serious and the approach, which was most likely to be considered “not a problem”. More detailed
observations about these maneuvers provided examples where the approach requires the truck to be at the
far left to enter the circle as problem. This places the trailer in the wrong position to proceed around a
circle without off tracking to the left enough to climb the center curbing. Other approach problems
included the approach not being wide enough, curbing and the situation where drivers are not using turn
signals making the timing of the entrance difficult for large trucks, especially in heavy traffic. Remarks
regarding the circular roadway included comments that the diameter is too small, examples of interior
curbing, and dangerous interactions with passenger vehicles. Poor signage naming the exiting street, last
minute lane changes by passenger vehicles, and “jumping” the trailer over an abrupt curb were cited as
departure problems.
Serious Problem
Exists
30%
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
Problem Exists but
Not So Serious
32%
No Problem Exists
The Approach
The Circular
56%
31%
Roadway
The Departure
29%
53%
TABLE 1 Distribution of Rankings for Roundabout Maneuver
37%
13%
18%
In the next set of questions, respondents were given a roundabout design feature specifically
created to accommodate large trucks and then asked to rank the feature as “not beneficial”, “somewhat
beneficial”, or “very beneficial”. Table 2 displays the distribution of the benefit rankings for the two
design features. The roundabout design features included a removable barrier which allowed trucks to
pass through the center of the roundabout but prevented other traffic from doing so and a second option
(offset approach) which allowed trucks to move straight through a roundabout using an offset pathway so
that the entrance would line up with the left approach (the driver would move to the left on the approach).
Not Beneficial
Somewhat Beneficial
Removable Barrier
32%
50%
Offset Approach
40%
42%
TABLE 2 Distribution of Benefit Ranking for Roundabout Design Features
Very Beneficial
18%
18%
Of those who provided further comments about each design feature, most felt that these solutions
were confusing and may create safety concerns that outweighed the possible benefits. When asked if the
respondent felt a need to provide more input to roundabout engineers, topics that emerged echoed those of
previous questions with concerns about the roundabout size, curbing, and planning which considered
large truck accommodation rising again.
The last portion of questions engaged the respondent in a discussion of several known roundabout
concerns. These concerns were posed as open-ended questions with the respondent directed to share their
TRB 2013 Annual Meeting
Paper revised from original submittal.
Park and Pierce
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
6
views on each. The following section lists each of the concerns and synthesizes the commentary into a
few descriptive bullet points.
1) “Low-boy” (low clearance) vehicles have problems with curbs over four inches in height.
 Serious concern for large trucks.
 Would like to see the curbing area as a flat road surface that could be textured to
discourage drivers from driving on it, but allow trucks additional space to operate.
 The main surface of the island should be no higher than 4” and have a sloping apron.
Gradual sloping is considered to alleviate this problem.
 Concerns relate to damage to equipment including frame rails, tires (especially on the
side wall as loaded trailers try to climb over the curb to circle the roundabout),
suspension, alignment (which results in tire, control, and fuel economy issues), and load
stability.
2) Fixed objects within the center of the roundabout cause problems.
 Oncoming traffic cannot be seen at night and it challenges the driver’s depth perception.
Visibility of vehicles or people that might be entering the roundabout, correctly, or
possibly in the wrong direction are not visible, thereby increasing the likelihood of an
accident.
 The fixed shrubs and other fixed objects will be damaged over time as longer vehicles
cannot go through without the trailer getting into the center of the roundabout. The fixed
objects will most likely be hit and damaged by the trailing rear of the trailer.
 The likelihood of problems is dependent on the ratio of the diameter of the roundabout
island. Of course, small circumference islands should not have fixed objects.
3) Slopes of circular roadway and truck aprons cause fear of rollover.
 Responses wavered on the likelihood of overturning due to roadway slope. Most
comments, whether they agreed or disagreed with the statement, noted that several factors
including the severity of the slope, posted speeds, and the nature of the freight being
hauled as factors that would influence the level of rollover fear.
4) Drivers do not understand what the truck apron is for and need education.
 Responses fluctuated between comments about professional truck drivers and passenger
car drivers. Most respondents who made remarks regarding professional drivers stated
that most know how to negotiate a roundabout but felt that this education was ineffective
in a poorly designed roundabout. The observations related to passenger car drivers
strongly recommended further education of the public not just about roundabout
navigation, but also about operating around large trucks in all scenarios.
Participants were also given the opportunity to provide supplementary comments beyond issues
not specifically addressed in the previous questions. Most participants, however, took this opportunity to
reiterate many of the previously discussed themes. The supplementary comments restated the need for
larger roundabout circumferences, more education to passenger vehicles, and called for a re-evaluation of
roundabout use on roadways that are heavily used by large trucks.
SUMMARY
Several key issues pertaining to the challenges experienced by commercial truck drivers while negotiating
roundabouts arose as recurring themes in the carrier feedback collected in this survey. These issues
included the need for larger roundabout circumferences, more education to drivers of passenger vehicles,
and a re-evaluation of roundabout design. Nearly two-thirds (73%) of respondents believed that
roundabouts were more problematic for large trucks than other types of intersections. Carriers
commented on roundabout navigation problems that are unique to large trucks, frequently citing small
TRB 2013 Annual Meeting
Paper revised from original submittal.
Park and Pierce
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
7
roundabout circumferences, design features that cause damage to the truck, and safe interaction with
passenger cars as operational concerns. When asked to consider the approach, circular roadway, and exit
of a roundabout, survey respondents most often cited the circular roadway as a serious problem. These
respondents remarked that the roundabout diameter is often too small, and cited examples of interior
curbing and dangerous interactions with passenger vehicles. Carriers were also asked to propose
solutions that would allow roundabouts to better accommodate large trucks without sacrificing safety and
operational efficiency. Carriers sought to ensure that proposed solutions were not confusing and did not
create safety concerns that outweighed the possible benefits. Proposed solutions again echoed concerns
raised in response to previous questions, with issues of roundabout size, curbing, and planning focused on
large truck accommodation arising frequently.
NEXT STEPS
This research collected and synthesized the most common concerns about roundabout navigation by large
trucks through a survey of motor carriers. The results of this research can be used to inform roundabout
designers and engineers of some of the problems experienced by large trucks in roundabouts, even when
large truck accommodating design features are present. Further research into the metrics and design
criteria of roundabout features which are thought to ease roundabout use for large trucks is necessary.
However, the research presented in this paper could be used as a catalyst for dialogue between the
trucking industry and roadway designers in which truck experiences with various roadway features can be
further explored. Through this discourse, the effect of roadway design features on driver behavior and
truck functionality and the resulting consequence on freight transportation and overall road safety may be
better understood.
TRB 2013 Annual Meeting
Paper revised from original submittal.
Park and Pierce
1
2
3
4
5
8
ACKNOWLEDGEMENT
ATRI would like to thank Gene Russell Sr., PE, PhD and Ranjit Godavarthy in the Department of Civil
Engineering at Kansas State University for their efforts to create and host the online survey presented in
this paper.
TRB 2013 Annual Meeting
Paper revised from original submittal.
Park and Pierce
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
9
REFERENCES
(1) “Roundabouts”. Federal Highway Administration Resource Center Safety and Design Team. [Online]
[Cited: July 2, 2012] http://www.fhwa.dot.gov/resourcecenter/teams/safety/safe_7rnd.cfm
(2) “Roundabouts in the United States”. National Cooperative Highway Research Program, Report No.
572. Washington, DC: Transportation Research Board. 2007.
(3) “Negotiation-Based Conflict Exposure Methodology in Roundabout Crash Pattern Analysis”. Zheng,
Dongxi et al. TRB 2010 Annual Meeting CD-ROM. Transportation Research Board of the
National Acadamies, Washington, D.C. 2009.
(4) “Heavy Goods Vehicle Accidents on Roundabouts: Parameters of Influence”. Cerezo, V. and
Gothie, M. Laboratoire Régional de Lyon – CETE de Lyon, France. 2006.
(5) “Benefit-Cost Analyses of Onboard Safety Systems: Technical Brief”. American Transportation
Research Institute, U.S. Department of Transportation, Federal Motor Carrier Safety
Administration, FMCSA-RRT-09-023. Washington, D.C. 2009.
(6) “Roundabouts: An Informational Guide (2nd ed.)”. Washington DC, USA: Transportation Research
Board of the National Academies, National Cooperative Highway Research Program, Report 672.
2010.
(7) “Accommodating Small and Large Users at Roundabouts”. Weber, P. and Button, N. Sustainability
in Development and Geometric Design for Roadways, Annual Conference of the Transportation
Association of Canada. Vancouver, British Columbia. 2009.
(8) “Comprehensive Truck Size and Weight Study: Volume 2, Chapter 3”. U.S. Department of
Transportation, Federal Highway Administration, FHWA-PL-00-029. Washington, D.C. 2000.
(9) “American Trucking Trends: 2012”. American Trucking Associations. Washington, D.C. 2012.
(10) “American Trucking Trends: 2005-2006”. American Trucking Associations. Washington, D.C.
2006.
TRB 2013 Annual Meeting
Paper revised from original submittal.