Injury severity as assessed by law enforcement officers on crash reports, particularly incapacitating injuries (severity = A on the KABCO scale, on which K denotes a fatal injury, A an incapacitating injury, B a non-incapacitating injury, C a possible injury, and O a property-damage-only crash, is used for estimating crash costs and, in turn, for allocating safety funds. The Crash Outcome Data Evaluation System (CODES) database reports injury severity assessment from both law enforcement officers using the KABCO scale and medical practitioners using the Maximum Abbreviated Injury Score (MAIS). The objective of this study was to analyze the accuracy of the injury severity ratings on Wisconsin crash reports by comparing crash data in the CODES database between 2008 and 2012. Results indicated that 66.6% of KABCO A crashes had only minor or moderate injury severities (MAIS 1 or 2); that is, two-thirds of crash victims' injury severities were overestimated. In addition, underestimation of injury severities occurred in 2.9% of all O, C, and B crashes. Further analyses found that injuries to all body regions statistically contributed to overestimation and underestimation as compared with injuries to body regions from all crash reports, with the exception of lower extremities for underestimated crashes. Several factors including gender, vehicle type, and the presence of alcohol significantly contributed to both overestimation and underestimation. Lighting conditions also affected underestimation. Spine, thorax, and abdomen or pelvic injuries were the injuries most frequently missed by law enforcement officers. The most common injuries found in the inaccurate crash reports were bone injuries, lacerations, abrasions, and contusions. These findings were used to develop guidance for law enforcement officers to assist in more accurate injury severity assessments.
Roundabouts are common alternatives to stop- and signal-controlled intersections and have grown in popularity in response to the promise to reduce traffic crash severity at intersections. In Wisconsin, more than 300 roundabouts have been installed. Studies of these intersections have found a 38% reduction in fatal and injury crashes. However, a 12% overall increase also was found, and this finding is not unique to Wisconsin. An increase in less-serious crashes can lead to a negative public perception about roundabout benefits. The causes of rear-end collisions (a common type of low-severity crash) were examined. Four years of crash reports from 55 roundabouts were analyzed along with the geometric conditions of the roundabouts. The 16- to 24-year-old driver age group represented a significantly higher proportion of involvement in rear-end collisions than in total crashes across the state. Negative binomial models were created for roundabout approaches. For combined one-lane and multilane roundabout approaches, annual average daily traffic, sawtooth pavement markings, and high deflection angles were significantly correlated with an increase in the expected number of rear-end collisions, and wider entry was significantly correlated with a decrease in the expected number of rear-end collisions. For one-lane approaches, “Yield” pavement markings led to an expected reduction in crashes, as did the presence of horizontal curves within 250 feet of a roundabout. These findings reflect the complexity of driving at roundabout approaches, especially for younger drivers. Results also indicate the importance of proper pavement markings at approaches.
Roundabouts reduce fatal and injury crashes at intersections when converted from other intersection control types. In Wisconsin, roundabouts have been linked to a 38% decrease in fatal and injury crashes. Part of this reduction can be attributed to crash types that result in the mitigation of more serious injuries. However, the reduction comes at a cost because other crash types, such as single-vehicle collisions, may increase. Six years of crash data on 53 roundabouts in Wisconsin were examined for crash causes and geometric characteristics that affected single-vehicle crashes. Weather and impaired driving, particularly by younger drivers, were primary causes for more than half of all single-vehicle crashes at the study roundabouts. Younger drivers (18 to 24 years of age) were involved in a significantly higher proportion of single-vehicle crashes than the total proportion of licensed drivers in that age group. Younger drivers were involved in approximately one-third of all crashes that involved impaired driving and in two-thirds of all speed-related single-vehicle crashes. A negative binomial model was constructed to estimate run-off-road crashes at approaches. It was found that roundabouts with higher approach speeds and higher traffic volumes experienced more run-off-road crashes. Landscaped central islands experienced significantly lower frequencies of run-off-road crashes.
Across the United States large discrepancies have been found between law enforcement officers’ injury severity assessments and medically assessed health outcomes of crash victims. This research investigated injury severity discrepancies across law enforcement agencies, analyzing linked crash and medical data for each crash victim from 2010 through 2019 for 520 Wisconsin law enforcement agencies. Serious injury (KABCO “A”) assessments were overestimated in 45% to 90% of crash victims, depending on the agency. Statewide the overestimation rate was 65% across all agencies; the State Patrol overestimated 65% of serious injury assessments, 60% for county sheriff offices, and 64% for municipal police departments. These discrepancies can skew safety estimates and affect the allocation of funds. KABCO definitions were changed to a federally mandated uniform standard in Wisconsin in 2017. Results from an interrupted time series analysis found no significant effects from the changed KABCO definitions, either immediate or over time. At county sheriff’s offices overestimation increased as a function of county population size, and decreased with increasing total reported crashes from a jurisdiction, suggesting workload negatively affects overestimation rate, whereas relative familiarity with crashes and their severities improve overestimation rates. Different trauma scales (MAIS and ISS) and serious injury thresholds were investigated, and ISS of nine was proposed for future KABCO comparisons. Findings show that although KABCO “A” assessment overestimation is an issue everywhere, the magnitude of the issue varies from agency to agency and underscores the importance of uniform injury severity training to ensure accurate serious injury surveillance across the United States.
Roundabout implementations at traditional intersections have been shown to be effective at reducing severe crashes. Roundabouts have also been implemented at interchange ramp terminals; however, limited research is available. In this study, 25 roundabout ramp terminal implementations were evaluated. The methodological approach consisted of Empirical Bayes for safety effectiveness and crash cost changes, crash type weighted distribution, crash rate analysis of bypass configuration, and cost of implementation. Roundabouts were effective at reducing fatal and injury crashes when replacing existing interchange diamond ramp terminals: 65% reduction for roundabouts replacing stop-controlled ramp terminals and 41% reduction for roundabouts replacing signal-controlled ramp terminals. Observed crash type weighted distributions are provided to visualize the frequency and location of crashes within roundabout ramp terminals for design considerations. Exit ramp and outside crossroad approaches with right-turn bypass showed significantly lower crash rates than designs without bypass. The crash cost analysis showed that roundabouts replacing diamond ramp terminals yielded crash cost savings of between $95,000 and $253,000 per site per year (69% to 54% decrease in crash costs). Considering crash costs savings only, the cost of implementation should be less than $1.9 million for a roundabout replacing a stop-controlled ramp terminal and less than $5.1 million for a roundabout replacing a signal-controlled ramp terminal to accomplish benefit-cost ratios greater than one for a service life cycle of 20 years. Costs are in 2019 dollars.
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