ROUNDABOUTS AND THE ACCOMODATION OF LARGE TRUCKS: A MOTOR CARRIER PERSPECTIVE

Transcription

1 ROUNDABOUTS AND THE ACCOMODATION OF LARGE TRUCKS: A MOTOR CARRIER PERSPECTIVE Word Count:, Text + 00 Figures =, Total Submitted July, 0 Lisa Park (Corresponding Author) Research Analyst American Transportation Research Institute 00 Franklin Way, SE Suite 0 Marietta, GA 00 (0) -0 Phone: 0--0 x. Fax: lpark@trucking.org David Pierce Research Associate American Transportation Research Institute 00 Franklin Way, SE Suite 0 Marietta, GA 00 Phone: 0--0 x. Fax: dpierce@trucking.org

2 Park and Pierce 0 ABSTRACT With nearly 00 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.

3 Park and Pierce 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. () 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,000 welldesigned roundabouts per year to reduce crashes and improve intersection safety. () 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. () Roundabout crashes typically fall into four classes: run-off-road, rear-end, sideswipe, and entering-circulating. () Contributing crash factors at roundabouts include driver sight distance, failure to yield to vehicles in the circulating lane, and high speed differentials. (,) 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. () 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 $00,0 to $,, depending on the type of crash. () Roundabouts should be designed considering the need to accommodate the largest vehicle likely to use the intersection. () 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. ()

4 Park and Pierce 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 0 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 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, 0 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. (), 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 -axle tractor/semi-trailer combinations in their fleet. This type of truck configuration represents about percent of the national truck fleet and more than percent of all combination trucks. () ANALYSIS Industry Demographics Of the 0 surveys completed, the majority of respondents () indicated using -axle tractor/semi-trailer configurations in their fleet and the population skewed towards the for-hire sector. Of those carriers, percent operated in the for-hire sector and the remaining 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 (.%) followed by the for-hire sector (.%) and other (.%) in 0. () 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 (%) was the most frequent response. Other carriers identified themselves as flatbed (%), less-than-truckload (%), private fleet/shipper (%),

5 Park and Pierce tanker (.%) and other (.%). Figure displays the number of carriers who identified with each carrier type. Nationally, the distribution of for-hire carriers is percent truckload, percent less than truckload and percent specialized. (0) 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 percent of the respondents followed by urban interstates, highways and freeways (%), urban major highways (%), urban local roads (%), rural major highways (%) and rural local roads (%). 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 (%) believed that roundabouts were more of a problem compared to other intersections and slightly less (%) 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 0 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 ' 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?

6 Park and Pierce 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 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 Problem Exists but No Problem Exists Exists Not So Serious The Approach 0% % % The Circular Roadway % % % The Departure % % % TABLE Distribution of Rankings for Roundabout Maneuver 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 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 Very Beneficial Removable Barrier % 0% % Offset Approach 0% % % TABLE Distribution of Benefit Ranking for Roundabout Design Features 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

7 Park and Pierce views on each. The following section lists each of the concerns and synthesizes the commentary into a few descriptive bullet points. ) 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 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. ) 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. ) 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. ) 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 (%) 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

8 Park and Pierce 0 0 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.

9 Park and Pierce 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.

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