Article

Determining the Effectiveness of an Advance LED Warning System for Rural Intersections

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Abstract

The majority of intersection-related fatal crashes occur at rural through-stop intersections. At these intersections, sight restrictions caused by vertical and horizontal curves negatively affect a driver's ability to safely accept a gap in the traffic stream. Static advance warning signs are sometimes installed at these intersections to warn drivers on the main through approaches that an intersection is ahead. These warning signs appear to be ineffective. A new advance LED warning system was developed and deployed at a rural through-stop intersection that had limited intersection sight distance because of a severe vertical curve. The warning system actively detected vehicles on all approaches and activated LED blinker warning signs for the conflicting movements. The research project included an analysis of driver behavior at the intersection, obtained through video data, and a survey of local residents and frequent users of the intersection. This paper presents the results of the research conducted to assess the effectiveness of this new LED warning system.

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... A few studies have examined the effectiveness of various ICWS countermeasures from many aspects. [5][6][7][8][9][10][11][12][13] Some positive impacts of the ICWS included reduced total and injury-only crashes, 5 6 decreased vehicle approaching speeds, [7][8][9] increased accepted gap sizes, 10 11 etc. Other studies identified more crashes within a short period following ICWS deployments, 12 or less compliance with the stop signs at treatment intersections. ...
... A few studies have examined the effectiveness of various ICWS countermeasures from many aspects. [5][6][7][8][9][10][11][12][13] Some positive impacts of the ICWS included reduced total and injury-only crashes, 5 6 decreased vehicle approaching speeds, [7][8][9] increased accepted gap sizes, 10 11 etc. Other studies identified more crashes within a short period following ICWS deployments, 12 or less compliance with the stop signs at treatment intersections. ...
... Previous studies have consistently demonstrated the ICWSs' effectiveness in reducing vehicle speeds on major approaches. [7][8][9] This effect could allow more reaction time for drivers on both major and minor approaches to proactively switch directions to avoid more direct and severe angle impacts during crossing or left turns. However, the possibility of drivers being distracted by the minor road ICWS signs, and failing to search for mainstream traffic when making right turns, cannot be ruled out, completely. ...
Article
Objective Intersection conflict warning systems (ICWSs) have been implemented at high-risk two-way stop-controlled intersections to prevent right-angle crashes and associated injuries. This study involved investigation of the impacts of ICWSs on crash reductions. Methods The study used a quasi-experimental design to analyse the potential causal relations between Minnesota’s ICWSs and various crash rate outcomes (including total, injury, non-injury, targeted right-angle and non-right-angle crashes) in pre-post analyses. A restricted randomisation method enabled identification of three controls to each ICWS treatment intersection, and included as many comparable intersection characteristics as possible. Annual crash rates (per year per intersection) were analysed over the same periods before and after system activation for treatment and control intersections in each matched group. Pre-crash data for 3 years and post-crash data for up to 5 years were included, ranging from 2010 to 2018. Negative binomial regression models with generalised estimating equations were applied to estimate the average, immediate and continuing treatment effects of ICWSs, through the difference-in-differences and difference-in-difference-in-difference approaches, respectively. Results The ICWS treatment was significantly associated with a decreasing trend for targeted right-angle crash rates posttreatment. Although not statistically significant, most crash rate outcomes appeared to be elevated immediately after treatment (statistically significant for sideswipe crashes only). Pre–post differences in average crash rates (over entire periods), except for incapacitating injury-related crashes, were not statistically significant between treatment and control intersections. Conclusions The study provided important insight into potential causal associations between intersection safety countermeasures and crashes at high-risk rural two-way stop-controlled intersections.
... Intersection Conflict Warning Systems (ICWS) have been used at rural intersections to warn drivers on the minor approach of on-coming traffic and to warn drivers on the main approach of vehicles entering from the minor approach (2). Early studies have indicated that ICWS can result in lower intersection approach speeds, reduced conflicts, improved compliance with traffic control, and improved gap selection (3)(4)(5)(6). Weidemann et al. (4) evaluated an intersection in Minnesota which had been instrumented with an ICWS. They found a 4.5% decrease in speed when the system was active compared with before installation. ...
... Early studies have indicated that ICWS can result in lower intersection approach speeds, reduced conflicts, improved compliance with traffic control, and improved gap selection (3)(4)(5)(6). Weidemann et al. (4) evaluated an intersection in Minnesota which had been instrumented with an ICWS. They found a 4.5% decrease in speed when the system was active compared with before installation. ...
... However, there has been some evidence that when the ICWS is not activated, drivers are less likely to comply with the stop sign and some sites have experienced minor crash increases (4). Weidemann et al. (4) found an increase in crashes (13%-24%). ...
Article
Full-text available
Rural intersections account for around 30% of crashes in rural areas and 6% of all fatal crashes. An Intersection Conflict Warning System (ICWS) is a unique solution to address rural intersection safety. ICWS are typically installed at the minor approaches to two-way stop-controlled intersections to reduce the number of fatalities. Studies indicate these systems result in lower intersection approach speeds, reduced conflicts, and improved driver-gap selection. However, some sites have experienced increases in the number of minor crashes. Although there are positive ICWS examples, their overall effectiveness is not well established. The objective of this research was to evaluate driving behavior at stop-controlled approaches with and without ICWS and to evaluate the spillover effect of ICWS on other adjacent control intersections where the treatment has not been applied. The study examined behavior at five intersections (treatment sites) in Minnesota where an ICWS was installed. For comparison, an additional five similar (control sites) were identified in proximity to each treatment intersection. Data were collected using a video camera array at three different time frames: before, one month, and 12 months after the installation of system. The data were analyzed using a critical gap approach. The analysis shows that the ICWS improved driver gap acceptance at the treatment sites, only at the 12-month period, and that there was no “spillover effect” at the adjacent control sites. When gap acceptance was further compared by type of stop, critical gap selection was shown to increase for drivers making both complete and rolling stops.
... Vehicle detectors are used to activate flashing roadside warning signs and alert drivers to the presence of vehicles on an adjacent approach (Thapa et al., 2018;Himes et al., 2016). It has been reported that these systems successfully reduce approach speeds (Weidemann et al., 2011;Thapa et al., 2018) as well as actual crashes (Himes et al., 2016). However, one study found that stop sign rollthroughs increased when the system was not active (Weidemann et al., 2011). ...
... It has been reported that these systems successfully reduce approach speeds (Weidemann et al., 2011;Thapa et al., 2018) as well as actual crashes (Himes et al., 2016). However, one study found that stop sign rollthroughs increased when the system was not active (Weidemann et al., 2011). More advanced smart intersection warning systems have also been developed which use radar sensors to measure the location, speed and acceleration of an approaching vehicle. ...
Article
The Rural Intersection Active Warning System (RIAWS) is an innovative road safety treatment designed to slow traffic on major approaches to a high-risk rural intersection when vehicles are turning or crossing into or out of the side roads, thus reducing fatal and serious casualties. A 2 × 2 experimental driving simulation study was undertaken which aimed to determine the impact of signage (RIAWS versus traditional painted) and sign content (80 km/h versus slow down) on drivers’ instantaneous speed at rural intersections. The driving simulator assessment was completed by 96 drivers aged between 18 and 80 years with a current WA C class licence (passenger vehicle). This provided a total of 384 observations. The results of a two-way ANOVA found a significant interaction effect between speed signage and sign content (F(1,3) = 11.78, p < 0.001). The RIAWS “80 km/h” sign resulted in significantly lower instantaneous speeds than all other types of signs including RIAWS “slow down signs (p < 0.001), traditional painted “80 km/h” signs (p = 0.023) and traditional painted “slow down” signs (p = 0.001). Overall, the study found that RIAWS “80 km/h” sign and not the RIAWS “slow down” sign provided the most effective option for reducing driver speeds on approach to rural intersections. Further research is needed to determine the most effective placement of the RIAWS “80 km/h” signs and how they perform on curved roads.
... A key assumption of the study was that a one month novelty period would allow motorists to become accustomed to the changes that were made to the test environment. The novelty periods in this study were assigned based on relevant literature and the time constraints of the project schedule (Gates, Hawkins, Chrysler, Carlson, Holick, and Spiegelman, 2004) (Smiley, 2012) (Weidemann, Kwon, Lund, and Boder, 2011). If the novelty period was too short, then the data collected may have been more of a snapshot instead of a measurement of the impact caused by the LED enhanced signs. ...
Article
Objective This study evaluated the effectiveness and potential safety benefits of a Rural Junction Active Warning System (RJAWS), which uses variable speed limit signs (VSLSs) to temporarily impose a reduced speed limit along the major road when another vehicle is approaching on the minor road or turning into the minor road from the far-side major leg. Methods The RJAWS was trialed at 4 3-leg rural junctions between 2-lane roads in South Australia. A quasi-experimental before–after analysis was conducted. The free-flow speed of vehicles along the junction major approaches was used as an indicator of the risk of a casualty crash with adjacent traffic. Events with activated and nonactivated VSLSs after the RJAWS installation were analyzed separately. Travel speed, speed limit compliance, and the relative risk of a casualty crash were compared. The potential risk of casualty crashes relative to traveling at the default speed limit was calculated based on a known relationship between travel speed and relative casualty risk for rural roads in South Australia. Results When the reduced speed limit signs are activated, the average travel speed along the major road is reduced between 11.3 and 22.1 km/h, with a consequent reduction of the expected average casualty risk between 42% and 65% compared to before the RJAWS installation. . Though compliance with the reduced posted speed limit was low, the RJAWS still proved effective in reducing travel speed because the majority of drivers traveled through the monitored junctions at speeds below the default speed limit when the sign was activated. Conclusions This evaluation indicated that the trialed RJAWS can potentially reduce the risk of fatal and serious injuries at junctions under conditions that may present the opportunity for an adjacent-direction collision with another vehicle. Extending the RJAWS installation to additional junctions is strongly suggested. Further monitoring is needed to determine whether safety benefits are sustained over the long term.
Conference Paper
Full-text available
Vehicle Activated Signs (VAS) aim to improve safety by warning drivers to exercise caution and/or reduce their travel speeds at particular locations. This study examined the effect of VAS on the speeds of drivers approaching selected rural intersections in southwestern Victoria. Six VAS were installed on rural undivided arterial approaches to T-intersections with limited sight distance from a side road. The VAS were activated by a movement sensor that detected the presence of vehicles on the side road. The speeds of main road drivers were recorded using pneumatic tubes. Arterial road speeds recorded at treatment sites were compared with speeds at selected comparison sites where standard static signs were present. Analysis of variance was used to compare mean speeds before and after treatment installation, controlling for any changes across comparison sites. At four sites, the treatment delivered statistically significant speed reductions of between 0.8 and 6.9 km/h. Increases in mean speeds of between 0.5 and 3.4 km/h were observed at the remaining two sites. The 85th percentile speeds followed mean speed trends. VAS may also deliver an increase in driver alertness. Other implications, including estimated crash reduction factors for this type of VAS application, are discussed further in this paper.
Article
Researchers examined the impacts of various sign conspicuity enhancements on traffic operations and driver behavior in Texas. Eight types of applications were evaluated: fluorescent yellow chevrons, fluorescent yellow chevron posts, fluorescent yellow curve signs, fluorescent yellow ramp advisory speed signs, fluorescent yellow stop ahead signs, fluorescent red stop signs, flashing red light-emitting diode (LED) stop signs, and a standard red border on speed limit signs. Fourteen sites were used for the evaluations. Traffic operations data collected before and after the sign upgrades included vehicle speeds, edge line encroachments, and stopping compliance. Many statistically significant beneficial results occurred, including the following: fluorescent yellow chevron signs produced a significant reduction in curve speeds and edge line encroachments, both the fluorescent red and LED stop sign treatments reduced the number of vehicles not fully stopping, and the standard red reflectorized border on the speed limit sign produced a significant improvement in speed limit compliance. The data showed no undesirable impacts for the measures of effectiveness for any of the signing treatments. On the basis of the findings, the researchers recommend fluorescent yellow chevrons for full implementation. The other fluorescent yellow signs evaluated in the research are recommended for implementation on an as-needed basis. Microprismatic stop signs and flashing LED stop signs are also recommended for implementation on an as-needed basis. Although found to be effective, the red border speed limit sign currently should be limited to experimental implementation, as permission is required from FHWA to install these signs. The fluorescent red stop sign is not commercially available at this time.
Article
The characteristics of traffic flow at rural, low-volume intersections controlled by stop signs and by intersection control beacons plus stop signs were examined. The measures of effectiveness included vehicular speeds, stop-sign violations, service delay, gap acceptance, and accidents. In addition, the effects of sight distance, traffic volume, and day and night conditions were also considered. It was found that intersection control beacons generally reduced vehicular speeds in the major directions, particularly at intersections with inadequate sight distance. The intersection control beacons had, in general, little or no effect on accepted or rejected gaps and on service delays. A large proportion of drivers (40 to 90%) violated stop-sign laws by not completely stopping at the intersections, which indicates that intersection control beacons were not effective in reducing stop-sign violations. Intersection control beacons did not appear to be effective in reducing accidents.
Article
Signs warning motorists that traffic on the cross street does not stop can be found at some intersections that are not all-way stop controlled. These "cross traffic" signs have been installed to furnish a special warning where some motorists on the minor approaches may incorrectly assume that the major crossing street also has stop signs. The variety of cross traffic signs in use lack uniformity of message, color, shape, and placement location. A literature review and two surveys were conducted to examine (a) present usage of cross traffic signs, (b) circumstances under which these signs have been installed, (c) studies of the effectiveness of the signs, and (d) future actions. The accident data reviewed offered mixed results about the signs' effectiveness: at some locations the signs appeared to reduce accident frequencies; at others, accidents continued despite their presence. If the intersections at which these signs have been installed are experiencing right-angle accidents due to a number of different factors, then countermeasures aimed at the right-of-way misperception problem may affect only some of the accidents. Expanded use of the signs could cause drivers to expect them at all two-way stop-controlled situations. More information on the long-term impact of the signs and a study of alternative approaches would help traffic engineers evaluate the desirability of these signs.
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A driver approaching a signalized intersection at which the light has turned yellow must make a decision whether to stop or proceed. A signal that is properly timed will generally provide an opportunity for a safe and legal maneuver. As approach speeds increase, however, executing a safe maneuver becomes more difficult. One countermeasure used to provide advance warning of an approaching intersection or an impending signal change at such an intersection is an advance warning signal (AWS). Several AWS systems have been installed throughout the United States, including four in Utah. The effectiveness of the Utah systems has been evaluated as a function of intersection safety by using crash history, speed distribution, and red-light running (RLR) metrics. The results of the research suggest that the contribution of the AWS systems to the safety and operation of the intersections can be interpreted as both positive and negative. The AWS systems have helped to maintain higher operating speeds and may also have improved capacity when vehicles do not need to stop. Meanwhile, speeds have been reduced in the time just before the onset of the yellow interval. However, the additional information provided to drivers may have encouraged some drivers to attempt to beat the light, as evidenced by an increase in RLR even with shortening of the lead flash time. The increase in RLR, however, has not led to an increase in the overall crash frequency or crash rate at these intersections.