Issues for Trucks Using Roundabouts: Design and Accommodation for Trucks

Chevuri, 2018. This study attempts to synthesize the research and knowledge of truck accommodation at roundabouts by synthesizing various research studies, reports, and articles; various subject areas such as roundabout designs for trucking activity, roundabout designs and accommodation strategies for specialized trucking activity such as oversized trucks, truck safety at roundabouts, and motor carrier perspective of trucking at roundabouts have been analyzed and relevant knowledge has been synthesized. This synthesis can be useful for researchers, designers, planners, and decision makers to determine effective ways to address specific trucking related issues at a roundabout.
One prominent issue identified at roundabouts is accommodating oversized trucks If roundabouts are not properly designed to accommodate these oversized trucks, they can damage the elevated parts of intersections. However, oversized trucks are permit vehicles that use the roadway with a special permit along with escort vehicles; also, their vehicle length and dimensions are significantly larger than the regular trucks. Designing the roundabout geometrics such as center island diameter, entry and exit lanes, circulatory roadway
lanes, etc., for oversized trucks can be very expensive and inefficient as the roundabout size increases significantly; further, such designs could negate the benefits of roundabouts which are obtained by slower speeds through compact
designs and curves. Accommodations can include:
1) Constructing fully traversable center islands at roundabouts so oversized trucks can go over them while traversing a roundabout avoiding the need to
build bigger roundabouts.
2) Constructing custom center island truck apron and external truck apron based on understanding the expected oversized truck traffic, their movement,
and swept path.
3) Allowing the oversized truck traffic to go in the opposite direction of the traffic at roundabout while traversing a left turn so that the need for additional
truck apron and/or traversable area would be decreased.
4) Building a straight passage through the center island so the oversized truck traffic which is anticipated to travel always through can be accommodated in the easiest possible way. This straight through passage however has to have gates so the normal vehicles can stay away from using it.
Some of the unique and common problems mentioned by truck drivers at roundabouts are:
1) Roundabouts being too small for larger trucks accommodation,
2) Instances of truck trailer encroaching into the center island,
3) Curbs being a hindrance for large trucks while making turns,
4) Truck trailers drifting and using second lane which can cause potential crashes and safety concerns,
5) Difficulty accelerating quickly to merge into traffic,
6) Passenger vehicle drivers not educated enough to give needed room for truck’s tractor trailer,
7) Elevated and sloping curbs causing truck hang-up problem,
8) Blind spot being created on the right side of the truck.

Godavarthy, Russell, Landman, 2016.The potential use of roundabouts with all their inherent benefits may be greatly diminished if they are not able to accommodate oversize/overweight (OSOW) vehicles, sometimes called “Superloads.” The problem, therefore, is how to accommodate OSOW vehicles without sacrificing the integrity, safety and other benefits of roundabouts. This study uses TORUS software to design six standard roundabouts using guidance from the latest Federal Highway Administration (FHWA) roundabout guide.
All the strategies investigated in this study proved to be effective in accommodating OSOW vehicles when compared to conventional ways of using a roundabout. This paper would need to be requested.

Godavarthy, Russell, 2015. Freight bottlenecks are a major cause of recurring congestion which accounts for about 40% of total vehicle hours of delay in the United States. Intersections for urban freight-roadway networks are one of the major freight bottlenecks and are considered to be a significant contributor for congestion and delay. Improving the efficiency at urban intersections with high truck traffic. With the roundabout intersection control being proven as a safe, operationally efficient, and environment-friendly control treatment, a greater use of roundabouts with urban freight roadway networks and their feasibility is analyzed in this study.
A recent study conducted by Federal Highway Administration (FHWA) found that freight bottlenecks caused upwards of 243 million truck hours of delay and that the direct user cost for this delay was about $7.8 billion per year. Signalized, arterial intersections account for a total of 18% of the delay—about 43 million hours of delay—for different freight routes that are comprised of urban freight corridors, intercity freight corridors, truck-access routes, and intermodal connectors.
The study compared and analyzed delay, congestion and emissions of roundabouts vs signalized intersections across cities of various sizes. Signalized intersection performance was analyzed using software, and theoretically compared with a roundabout control.
It was concluded that the roundabouts in Kansas’ small and medium cities’ freight roadway networks could reduce the delay for the trucks and other vehicles, could decrease congestion, and could contribute to improved traffic flow - although the study also noted that not all intersections on an urban freight-roadway are suitable for roundabouts.

Godavarthy, 2012. It has been well documented that roundabouts can offer several safety and operational benefits over signalized and stop controlled intersection alternatives. However the growing use of roundabouts and their benefits could be greatly diminished because they may not be well designed for large trucks, or to accommodate oversize/overweight (OSOW) vehicles which may be essential to a state’s industry and economy. This dissertation addresses concepts to better design roundabouts for use by owners/operators of typical large trucks, and that will also accommodate OSOW vehicles where appropriate. Roundabout safety generally decreases with increased roundabout size, wider lanes and larger radii, the geometric parameters that benefit large trucks and OSOW, thus a better balance is needed.
This study accomplishes this balance by initially reviewing and incorporating those portions of the study “Accommodating Oversize Overweight Vehicles at Roundabouts” that were researched, completed and written by the author of this dissertation, and which compiled current practice, research and concerns by various U.S. states and concerns of the trucking industry, by conducting four different surveys. Then to meet these concerns expressed by survey respondents, a great number of possible accommodation, strategies and design templates were developed by using existing design software. An evaluation method was also developed.

Two additional, needed studies, not previously reported in any published literature, addressed : 1. a vertical, ground clearance analysis, and 2. a study of the use of roundabouts in urban freight networks to incorporate their inherent benefits ,such as, reducing congestion, delay and pollution.

The first analysis described above was conducted by using software with 3D analysis capabilities to check and recommend critical vertical grades and maximum dimensions for a range of large truck types and OSOW vehicle configurations. Guidelines were developed to avoid problems of low, ground clearance vehicles scraping roundabout surfaces (“hanging up”).

The second study used existing software that relates intersection types to intersection traffic flow efficiency and related pollution, on a number of routing scenarios to test the hypothesis that integration of roundabouts in these freight networks improves traffic flow, and decreases delay, congestion and pollution. The results were mixed but the procedure is sound and should be beneficial for future use by researchers and decision makers.

Kirk, 2004. An ODOT research report prepared before roundabouts were a prominent feature on state highways. This was included because it gives a view of other concerns expressed by the trucking industry.

Newcombe, 2018. An awards proposal outlining a $5.7M project in BC. This project replaced a geometrically substandard multi-leg intersection on Highway 97A in Sicamous, BC with a 4-leg modern roundabout. While truck aprons are a standard feature in modern roundabouts, this design included “sequential designation of space” by using a combination of painted and physical islands. In this manner, passenger vehicles and light trucks operate within the paint lines; heavier vehicles may need to operate outside the paint lines but within pavement areas; larger trucks (WB20, etc.) will need to use the coloured concrete central island apron; and very large permit vehicles will need to also use the coloured concrete aprons on the splitter islands.
Extremely oversized vehicles operating under permits and with pilot vehicles, can traverse the roundabout in a counter-flow operation. The team used very low custom curbs, surrounding a rollover median island on one approach to the roundabout, to accommodate these vehicles. The colour
and materials for this median are consistent with the adjoining median preceding and following this section to avoid confusion by conventional traffic.

Pecchini, Roncella, et al. 2017. Correctly designed roundabouts proved to have positive safety and functional performances. However, they are also affected by peculiar disadvantages. In particular, they are difficult to maneuver, especially for heavy vehicle drivers. Despite these concerns, there are currently no driving workload metrics devoted to roundabouts. A novel methodological approach is proposed for trying to quantify workload impinging on heavy vehicle drivers when maneuvering through complex at-grade intersections. Proper acquisition of input data constitutes the starting point for future research about ascertainment of workload for these particular road scenarios. The described procedure enables recording steering wheel angles performed by a driver when maneuvering an articulated lorry through a complex at-grade intersection. A field trial was carried out for verifying the practical feasibility of proposed method in capturing driver’s steering behavior. Dynamic data acquired via global navigation satellite system instrumentation were related to actual driver’s steering wheel behavior captured by camera frames. As a complement to the experiment, selected steering behavior metrics were calculated. Steering Entropy attributed a high difficulty level to the maneuvers performed through the roundabout, whereas High Frequency Component and Steering Reversal Rate showed intensity and occurrences of driver’s corrections needed for controlling position of the semitrailer at the ring. It appears that even a single roundabout may represent an arduous task for drivers. The study concludes with recommendations for further research about workload imposed by roundabouts to heavy vehicle drivers, with special attention to successions of closely spaced roundabouts. This article would need to be requested.

Russell, Landman, Godavarthy, 2013. Safety and traffic operational benefits of roundabouts for the typical vehicle fleet (automobiles and small trucks) have been well documented. Although roundabouts have been in widespread use in other countries for many years, their general use in the United States began only in the recent past. 1990 is generally accepted as the year the first modern roundabouts were built in the United States (US), but their use is growing. Roundabouts can offer several advantages over signalized and stop-controlled intersection alternatives, including better overall safety performance, lower delays, shorter queues, better management of speed, and opportunities for community enhancement features. However, potential use of roundabouts with all their benefits may be greatly diminished if they cannot accommodate oversize/overweight vehicles (OSOW). Accommodating OSOW at roundabouts is the central issue and the need for this research. Note that the acronym OSOW has been used in this report as a universal term, generally understood to mean a permitted vehicle. OSOWs impact pavement structure, roadway geometrics, and traffic operations. These issues are discussed in the report. OSOWs are a reality for American industry and often critical for certain industries. A better understanding and sharing of current practices is essential for states that permit such movement, and the industry which must rely on state highways and a permit to deliver large loads. Thus, the main objectives of this report are to compile current practice and research by various states and countries related to the effects OSOW have on roundabout location, design, and accommodation. Second, the research will attempt to fill in information gaps with respect to roundabout design and operations for this class of vehicles. A literature review uncovered no published reports on OSOW accommodation per se; however, much information on the advantages of having designated truck and OSOW networks is analyzed and reported. The authors make an argument that states should consider conducting a study to develop a freight network, which includes segments where OSOW need to be accommodated, in accordance with state and federal commerce laws and policies and the state’s economy. The study should include determining all motor vehicles whose size and turning movements are critical to developing routes on which all segments will accommodate these vehicle. To obtain information on the state-of-the–art of OSOW accommodation, the authors turned to personal contacts, unpublished material, case studies and surveys. Examples of accommodating OSOW in general, and various turning movements, found in the literature, surveys, and personal contacts are provided in the report as examples of ideas and concepts that could be considered, and possibly adapted to the needs of a specific site. From all surveys and contacts made during the course of this investigation, based on the most mentioned concern, the authors conclude that vertical ground clearance in general, and curbs in particular, are a major problem for large trucks and OSOW and definitely need to be mitigated whenever OSOW need to be accommodated. The authors conclude that ground clearance is an issue that has not been given as much attention as it deserves and must be addressed. The authors further conclude that three inches should be considered as a maximum height of splitter islands, truck aprons and curbs. Many other issues uncovered by the surveys are presented and discussed in the report. Numerous ideas are presented and design strategies are illustrated. The authors primary conclusion from conducting great numbers of vehicle path simulations is that, given the knowledge of what OSOW need to be accommodated, and their turning characteristics, any knowledgeable designer can do it, provided that right of way is available. It is up to the state to determine the economic benefits or dis-benefits of doing so. A final section of the report presents guidelines developed by Wisconsin DOT to check and avoid low, ground clearance vehicles (“low boys”) from scraping bottom while traversing roundabouts (“hang ups”), believed to be one of the first such studies in the USA. The authors present over three pages of other conclusions and recommendations, based on the literature reviewed, four surveys, examples of OSOW accommodation obtained from personal contacts, numerous OSOW simulations on various roundabout scenarios, the seven OSOW check vehicles used, and the low ground clearance concern that was the number one reported concern of the trucking industry.

Steel, Eng, et al. 2007. This paper considers whether or not roundabouts are a suitable improvement option as well as identifying and discussing some of the design and operational considerations given an Alberta context. These considerations include:
• The appropriate design vehicle.
• The type of collisions mitigated.
• The traffic volumes accommodated.
• Approach and circumnavigating speeds.
• Public education.
• Divided/undivided highways.
Designing for truck traffic is considered.

Weber, Eng, 2011. This paper builds upon one submitted for the 2009 conference that discussed “small” users (pedestrians and cyclists) and “large” users (trucks) of roundabouts. It covers the topic of large commercial vehicles at roundabouts in more detail. Several horizontal design treatments exist to accommodate large commercial vehicles at roundabouts. This paper examines the use of widened entries and exits, partially traversable truck aprons, gated pass-throughs, and right-turn by-pass lanes. Unlike single-lane roundabouts, no special geometric treatments are necessarily needed to physically accommodate large commercial vehicles at multi-lane roundabouts. However there are still a number of considerations in terms of lane use. This paper discusses whether to allow for trucks to overtrack adjacent lanes in a roundabout, and whether to install lane lines in the circulatory road. Two case studies are then used to describe recent projects undertaken in northern Alberta to accommodate one or more over-dimensional vehicles through a roundabout.
The first case study summarizes the preliminary design of a multi-lane roundabout to accommodate an over-dimensional vehicle making a through movement at the intersection of Highway 63 and Highway 69 in Fort McMurray, Alberta. The second case study summarizes the preliminary design of a single-lane roundabout to accommodate several over-dimensional vehicles making turning movements at the intersection of Highway 55 and Highway 892 west of Cold Lake, Alberta. In both projects a number of the treatments described in this paper were employed to accommodate the vehicles without compromising the inherent safety benefits of the roundabout.

Yin, Qiu., 2012. In order to demonstrate the analysis procedures for feasibility study of roundabouts, five case studies on Alberta and Saskatchewan rural arterial highways, including signalized and stop controlled intersections as well as an interchange ramp terminal were analyzed. They all have either long delays or operational and safety concerns that improvements are required. In the case studies, future intersection turning volumes were predicted to evaluate traffic operations and capacity of each alternative. Cross comparison of traffic operations was made between stop controlled intersections, signal controls, single-lane and two-lane roundabouts.
These case studies demonstrated intersections where roundabout is a good solution and locations where roundabout is not the best choice. Based on the study, it is concluded that in order for a roundabout to be feasible for an intersection, it should have adequate capacity, expected safety performance and superior economic value than other competing alternatives.
Case studies on several existing intersections found that, under most circumstances, roundabouts are safer than other intersection forms. The capacity of single-lane roundabouts is higher than all-way-stop controlled intersections but lower than signalized intersections with properly designed through and turning lanes. The capacity of two lane roundabouts is usually lower than channelized intersections with two through lanes in each direction and exclusive left-turn lanes.
Innovative use of roundabouts at some interchange terminals can not only provide safety benefits, but also offer operational advantages and avoid unnecessary stops, which is especially beneficial to large trucks using the roundabout

Gkoutzini, Lemonakis, 2020. Due to their evident benefits roundabouts are widespread among the congested urban road networks. The primary aims of the roundabouts are to improve safety, traffic and environmental conditions, which derive from their proper design. Vehicle swept path analysis is considered a crucial parameter in the design of a roundabout. The accurate prediction of the vehicle’s movement ensures a safe route and identifies the conflict areas, at the entry, exit and along the circulatory roadway especially in a 2-lane roundabout where accidents are over-represented. The purpose of this paper is to investigate vehicle’s turning path in 2-lane roundabouts. The large trucks are of particular interest, because they demand more space in their motion. Consequently, the dimensions of the roundabouts are determined by the turning paths of the heavy vehicles and buses. Therefore, in order to perform swept path analysis, the turning paths of different type of large vehicles in roundabouts with different diameter have to be computed. Moreover, the overlap of the turning paths of two vehicles traveling simultaneously in a two- lane roundabout will be investigated. In the recent years, roundabouts have also become increasingly popular in Greece. In fact, in the city of Volos four roundabouts have been constructed in the last two years. Gkoutzini, Lemonakis, et al. 2020. The two of them have been chosen to be investigated in terms of geometry and safety based on the preceding analysis. This paper would need to be requested.

Jensen, 2015. The height of central islands, sight distances, pavement markings and signage seem to have some influence on safety at single-lane roundabouts. The paper presents new information based upon a before-after safety study of converting intersections to 265 single-lane roundabouts in Denmark. Results from previous studies on these topics are included in the paper for comparison and discussion.
Non-transparent central islands higher than 1.9 meters produce better safety effects compared to lower central islands at single-lane roundabouts. A consequence of high central islands is fewer accidents between entering and circulating vehicles. Certain approach sight distances may worsen safety at urban single-lane roundabouts. If upstream and circulating approach sight is given to approaching road users about 17-40 meters before the yield line then safety is not good. If there is a truck apron around the central island then marking an edge line between the truck apron and the circulation seems to improve safety particularly at urban single-lane roundabouts. A two meters wide truck apron seems to be safest. Yield ahead signs and markings, roundabout plagues, destination signs and rumble strips all prior to the entry of single-lane roundabouts seem to improve safety considerably.

Waddell, Gingrich, Lenters, 2009. Roundabout design has pitfalls that guides cannot easily address. The composition of a roundabout involves trade-offs and optimization for safety, capacity and cost competing within the site context. Large vehicles pose additional challenges even to experienced designers. The article outlines some negative experiences of poorly designed roundabouts, and the expense to make them accessible to all vehicles.
Truck overturns present a special concern. Contributing factors can be complex. In most cases, truck overturns at U.S. roundabouts have been attributed to excessive speed or hard braking on adverse superelevation. The United Kingdom has about 20,000 roundabouts and 50–60 injury crashes per year involving truck overturns. Most are lowspeed and do not cause serious injury. The Transport Research Laboratory (TRL) reports five common characteristics of roundabouts with truck overturns:
1. long, straight, high-speed approach;
2. inadequate entry deflection;
3. low circulating flow past the entry;
4. clear visibility to the left (U.S. left)
5. significant tightening of radius part
way around the roundabout.
The U.K. Highways Agency adds three features that may contribute to overturns:
1. excessive grade breaks/cross-fall
changes on circulatory roadway or exits;
2. excessive adverse superelevation on
the outside lane of the circulatory roadway; and
3. excessive entry path deflection.