Facilitating bicycle travel using innovative intersection pavement markings.

INTRODUCTION: In an effort to facilitate bicycle travel through intersections, newer traffic control devices have been applied, including the bike box (a space for bicycles to stop on a red signal ahead of the motor-vehicle stop bar) and the two-stage turn queue box (a space where turning bicyclists can wait before making the second stage of a two-stage turn). This study evaluated the effects of two bike boxes and two turn boxes installed in 2014 at an intersection in Charlottesville, Virginia. METHODS: Videos collected during three days before the changes (non-consecutive over a one-month period), and five days after the changes (non-consecutive in the fall and spring seasons) provided volume counts and tallies of traffic infractions and conflict events such as near-misses. Data were prepared in order to pair the before and after periods, resulting in eight 12-h sets of observations starting at 7:30 a.m., each with 48 time intervals of 15 min. Histograms indicated that the data departed severely from a normal distribution (due to many 15-min intervals with no events), meaning a typical statistical test such as t-test was not appropriate, so the Wilcoxon signed-rank test was employed to compare the before and after periods. To take advantage of the paired structure of the data (i.e., before and after), a matched-pair version of the test was performed. Additional tests were performed after a partial re-review of data to examine observational variability concerns. RESULTS: Results were mixed and indicated that rates of traffic infractions decreased for some types of infractions and for some intersection approaches but increased for others. Some bicyclists used the new markings properly, but some used them improperly or failed to use them.

What affects annual changes in traffic safety? A macroscopic perspective in Virginia.

INTRODUCTION: Virginia saw a 20% reduction in traffic fatalities in 2008, an unprecedented annual reduction since 1950, and safety stakeholders in Virginia were intrigued about what caused such large a reduction and more generally what affects traffic safety from a macroscopic perspective. METHOD: This study attempted to find factors associated with such a reduction using historical data of Virginia. Specifically, the study related 18 factors to seven traffic safety measures. RESULTS: In terms of annual changes, the study found that typical crash exposures were not generally associated with the seven measures, while two economic indicators (unemployment rate and U.S. Consumer Price Index [CPI]) were strongly associated with most of them. CONCLUSIONS: Annual changes in the CPI and unemployment rate account for about half of the annual changes in total and fatal crash counts, respectively. On average, a 1 point increase in CPI and a 1% increase in the unemployment rate are associated with about 2,500 fewer traffic crashes and about 40 fewer fatal crashes annually in Virginia, respectively.

Differences in traffic violations and at-fault crashes between license suspension and revocation.

Upon conviction for particular traffic offenses, drivers can have their licenses revoked. Drivers who receive license revocation have an opportunity to apply for a sentence reduction, and some of those who apply receive a reduced sanction--license suspension. There may be differences between drivers whose license was revoked as originally sentenced and drivers who received the reduced sanction of license suspension with regard to traffic violations and crashes after driving privileges are restored. This study verified the differences during the follow-up periods of 6, 12, and 18 months using analysis of covariance and the t-test with stratified samples based on the police profiles of approximately 154,000 drivers in South Korea. The study found that drivers in the group whose license had been suspended committed traffic violations and caused traffic crashes less often for all time periods than those whose license had been revoked. However, omitted factors such as the attitude of suspended drivers and exposure to traffic violations and crashes (e.g., driving frequency after license reinstatement), are likely to affect the findings; thus, caution should be exercised when the findings are referenced for policy implications.

Potential risk of using General Estimates System: bicycle safety.

Beneficial effects of bicycle helmet use have been reported mostly based on medical or survey data collected from hospitals. This study was to examine the validity of the United States General Estimates System (GES) database familiar to many transportation professionals for a beneficial effect of helmet use in reducing the severity of injury to bicyclists and found potential risk of erroneous conclusions that can be drawn by a narrowly focused study when the GES database is used. Although the focus of the study was on bicycle helmet use, its findings regarding potential risk might be true for any type of traffic safety study using the GES data. A partial proportional odds model reflecting intrinsic ordering of injury severity was mainly used. About 16,000 bicycle-involved traffic crash records occurring in 2003 through 2008 in the United States were extracted from the GES database. Using the 2003-2008 GES data, a beneficial effect of helmet use was found in 2007, yet a detrimental effect in 2004 and no effect in 2003, 2005, 2006, and 2008, which are contrary to the past findings from medical or hospital survey data. It was speculated that these mixed results might be attributable to a possible lack of representation of the GES data for bicycle-involved traffic crashes, which may be supported by the findings, such as the average helmet use rates at the time of the crashes varying from 12% in 2004 to 38% in 2008. This suggests that the GES data may not be a reliable source for studying narrowly focused issues such as the effect of helmet use. A considerable fluctuation over years in basic statistical values (e.g., average) of variables of interest (e.g., helmet use) may be an indication of a possible lack of representation of the GES data. In such a case, caution should be exercised in interpreting and generalizing analysis results.

Stop versus yield on pedestrian-involved fatal crashes in the United States.

In an effort to improve pedestrian safety, several states in the United States changed their pedestrian laws by changing the requirement that drivers yield to pedestrians in crosswalks to a requirement that drivers stop for pedestrians in crosswalks. This study examined whether this change had an effect on pedestrian safety in the United States, with its focus on low-speed roads. To examine the association between changes in pedestrian laws and changes in pedestrian-involved fatal crashes, three approaches were employed: before-after analysis, time-series analysis, and cross-sectional analysis. Pedestrian-involved fatal traffic crashes on low-speed roads were extracted from the U.S. national fatal crash database, the Fatality Analysis Reporting System (FARS), from 1980 through 2005. This study found no statistically significant reduction in pedestrian-involved fatal crashes attributable to changes in the laws, yet this finding is not definitive because of study limitations such as the omission of relevant exposure data.

Overall injury risk to different drivers: combining exposure, frequency, and severity models.

Traffic crash risk assessments should incorporate appropriate exposure data. However, existing US nationwide crash data sets, the NASS General Estimates System (GES) and the Fatality Analysis Reporting System (FARS), do not contain information on driver or vehicle exposure. In order to obtain appropriate exposure data, this work estimates vehicle miles driven (VMD) by different drivers using the Nationwide Personal Transportation Survey (NPTS). These results are combined with annual crash rates and injury severity information from the GES for a comprehensive assessment of overall risk to different drivers across vehicle classes. Data are distinguished by driver age, gender, vehicle type, crash type (rollover versus non-rollover), and injury severity. After correcting for drivers' crash exposure, results indicate that young drivers are far more crash prone than other drivers (per VMD) and that drivers of sports utility vehicles (SUVs) and pickups (PUs) are more likely to be involved in rollover crashes than those driving passenger cars. Although, the results suggest that drivers of SUVs are generally much less crash prone than drivers of passenger cars, the rollover propensity of SUVs and the severity of that crash type offset many of the incident benefits for SUV drivers.

Driver injury severity: an application of ordered probit models.

This paper describes the use of ordered probit models to examine the risk of different injury levels sustained under all crash types, two-vehicle crashes, and single-vehicle crashes. The results suggest that pickups and sport utility vehicles are less safe than passenger cars under single-vehicle crash conditions. In two-vehicle crashes, however, these vehicle types are associated with less severe injuries for their drivers and more severe injuries for occupants of their collision partners. Other conclusions also are presented; for example. the results indicate that males and younger drivers in newer vehicles at lower speeds sustain less severe injuries.