Safety evaluation of roadway segments provided with Safety Edge in Iowa

Pavement edge drop-off is the vertical difference in elevation between the paved roadway and the adjacent ground. It is a serious safety concern for vehicles that goes off the track and encounters a drop-off. The errant vehicles, in order to restore their position back on the paved road, exert a greater amount of force which may result in loss of control for the driver. This may indicate an increase in the possibility of lane departure crashes, rollovers or head on collisions. According to an estimation by the Federal Highway Administration about 11,000 people suffers from injuries and about 160 people lose their lives each year in crashes related to unsafe pavement edges in the United States. Safety Edge, on the other hand, is a design feature that creates a fillet along the edge of the pavement of the roadway that allows drivers, who drift off roadways, to return safely to the roads. This study intended to conduct a safety evaluation of road segments provided with Safety Edge in Iowa. Thus a before and after crash analysis was conducted to estimate any reduction in crashes in the after period of installation. This research also looked into the road and traffic characteristics that significantly affected the crashes on road segments provided with Safety Edge. A total length of 483 miles of roadway segments installed with Safety Edge was identified all over Iowa. Roadway, traffic, lane characteristics and crashes on the treatment segments for the study period of eleven years from 2004 to 2011 was obtained from Iowa Department of Transportation. A Preliminary before and after crash analysis for all types of crashes showed a 50% reduction in all types of fatal crashes, 18.5% reduction in all types of property damage only (PDO) crashes and an overall decrease of 19% for all types of total crashes. A preliminary before and after crash analysis for target crashes showed a 75% reduction in Target fatal crashes, 1% increase in target PDO crashes and overall 17% reduction in total target crashes. The crash data which is a form of count data was analyzed using negative binomial regression. Positive safety impact of installation of Safety Edges was observed for almost all the statistical models (except for property damage only target crashes), as the crashes in the after period was observed to be less than that of the before period. Both scenarios of all types of crashes and target crashes were considered separately in the study. The variables that significantly affected the different crash models were average annual daily traffic (AADT), shoulder width, Rural/Urban indicator, and surface width. Negative Binomial Models for All types of KABCO crashes (all crash severity levels taken together) showed 21% reduction in crashes in the after period. The percentage reduction of all types of injury (KABC) crashes was 20%. For all types of PDO crashes the reduction was seen to be again 20%. Negative Binomial Models for target crashes showed 16.3% reduction in target KABCO crashes and 2.4% increase in target PDO crashes, along with 21% reduction in all types of KABCO crashes, and 20 % reduction in all types of PDO crashes. The results indicated that Safety Edge installation may also be able to reduce the severity of a crash

Safety Edge Crash Modification Factors

This study evaluated the safety impact of the Safety Edge for construction projects in 2010 and 2011 in Iowa to assess the effectiveness of the treatment in reducing crashes

Analysis of Stopping Behavior at Rural T-Intersections Using Naturalistic Driving Study Data

Rural intersections account for around 30% of crashes in rural areas and 6% of all fatal crashes, representing a significant but poorly understood safety problem. Crashes at rural intersections are also problematic since high speeds on intersection approaches are present which can exacerbate the impact of a crash. Additionally, rural areas are often underserved with EMS services which can further contribute to negative crash outcomes. This paper describes an analysis of driver stopping behavior at rural T-intersections using the SHRP 2 Naturalistic Driving Study data. Type of stop was used as a safety surrogate measure using full/rolling stops compared to non-stops. Time series traces were obtained for 157 drivers at 87 unique intersections resulting in 1277 samples at the stop controlled approach for T-intersections. Roadway (i.e. number of lanes, presence of skew, speed limit, presence of stop bar or other traffic control devices), driver (age, gender, speeding), and environmental characteristics (time of day, presence of rain) were reduced and included as independent variables. Results of a logistic regression model indicated drivers were less likely to stop during the nighttime. However presence of intersection lighting increased the likelihood of full/rolling stops. Presence of intersection skew was shown to negatively impact stopping behavior. Additionally drivers who were traveling over the posted speed limit upstream of the intersection approach were less likely to stop at the approach stop sign.This article is published as Oneyear, N. , Hallmark, S. , Goswamy, A. , Thapa, R. and Basulto-Elias, G. (2023) Analysis of Stopping Behavior at Rural T-Intersections Using Naturalistic Driving Study Data. Journal of Transportation Technologies, 13, 208-221. https://doi.org/10.4236/jtts.2023.132010. Posted with permission

Safety evaluation of roadway segments provided with Safety Edge in Iowa

Pavement edge drop-off is the vertical difference in elevation between the paved roadway and the adjacent ground. It is a serious safety concern for vehicles that goes off the track and encounters a drop-off. The errant vehicles, in order to restore their position back on the paved road, exert a greater amount of force which may result in loss of control for the driver. This may indicate an increase in the possibility of lane departure crashes, rollovers or head on collisions. According to an estimation by the Federal Highway Administration about 11,000 people suffers from injuries and about 160 people lose their lives each year in crashes related to unsafe pavement edges in the United States. Safety Edge, on the other hand, is a design feature that creates a fillet along the edge of the pavement of the roadway that allows drivers, who drift off roadways, to return safely to the roads. This study intended to conduct a safety evaluation of road segments provided with Safety Edge in Iowa. Thus a before and after crash analysis was conducted to estimate any reduction in crashes in the after period of installation. This research also looked into the road and traffic characteristics that significantly affected the crashes on road segments provided with Safety Edge. A total length of 483 miles of roadway segments installed with Safety Edge was identified all over Iowa. Roadway, traffic, lane characteristics and crashes on the treatment segments for the study period of eleven years from 2004 to 2011 was obtained from Iowa Department of Transportation. A Preliminary before and after crash analysis for all types of crashes showed a 50% reduction in all types of fatal crashes, 18.5% reduction in all types of property damage only (PDO) crashes and an overall decrease of 19% for all types of total crashes. A preliminary before and after crash analysis for target crashes showed a 75% reduction in Target fatal crashes, 1% increase in target PDO crashes and overall 17% reduction in total target crashes. The crash data which is a form of count data was analyzed using negative binomial regression. Positive safety impact of installation of Safety Edges was observed for almost all the statistical models (except for property damage only target crashes), as the crashes in the after period was observed to be less than that of the before period. Both scenarios of all types of crashes and target crashes were considered separately in the study. The variables that significantly affected the different crash models were average annual daily traffic (AADT), shoulder width, Rural/Urban indicator, and surface width. Negative Binomial Models for All types of KABCO crashes (all crash severity levels taken together) showed 21% reduction in crashes in the after period. The percentage reduction of all types of injury (KABC) crashes was 20%. For all types of PDO crashes the reduction was seen to be again 20%. Negative Binomial Models for target crashes showed 16.3% reduction in target KABCO crashes and 2.4% increase in target PDO crashes, along with 21% reduction in all types of KABCO crashes, and 20 % reduction in all types of PDO crashes. The results indicated that Safety Edge installation may also be able to reduce the severity of a crash.</p

Evaluation of work zone safety using the SHRP2 naturalistic driving study data

Work zones provide challenging and hazardous conditions not only for vehicle drivers, but also for highway workers who are injured or killed by errant vehicles. Over, 96,000 work zone crashes occurred in 2015 which equates to a work zone crash every 5.4 minutes. Several factors have been noted as contributing to work zone crashes. Driver factors have not been as well studied as other factors. The main objective of this study was to evaluate safety in work zones utilizing the SHRP2, Roadway Information Database (511 data) to identify potential work-zones. The study looked into the effectiveness of each temporary traffic control device on drivers’ change in speed on four-lane and multi-lane divided highways. The study also evaluated drivers’ lane change behavior on freeways with lane closure. The research team manually coded the locations of work zone features starting from first work-zone sign to the end of work-zone. The change in speed from a point upstream of the legibility distance of each work zone feature was compared to the speed just past the feature. Driver distraction and eye glance were also included. A linear mixed effects model was used to predict drivers’ change in speed in the work zone. For work zones on four-lane divided highways, speed feedback signs, lane end sign, and changeable message signs were found to be effective in reducing driver speed before the merge point. Non-forward related glance was seen to increase driver speed inside the work zone. Work zone speed limit signs were seen to be more effective within half mile inside a work zone. Presence of static work zone signs were more effective when the cones were placed as channelizing device inside the work zone. Vertical panels as channelizing device were used to decrease driver speed more effectively compared to concrete and cones. The change in speed model for multilane work zones showed static work zone signs to be effective in the upstream portion of start of taper of a work zone. Work zone speed limit signs are effective when placed within half mile upstream. Lane end signs are effective in all the sections of locations in the downstream model. Drivers reduced speed due to presence of any worker or equipment inside the work zone. Driver’s lane change behavior in work zones with lane closure on four-lane divided work zones were analyzed. It was seen that with presence of rear accommodating vehicle in the open lane, the drivers tend to merge early in a lane closure scenario in a four-lane divided (farther from work zone activity area). Similarly, presence of enforcement sign before merging, tends to increase distance of lane merge from the end of taper showing that the drivers merge early in a lane closure scenario in a four-lane divided. Non-forward related glance was associated with drivers merging early in a lane closure scenario in a four-lane divided. The study also showed that driver moving over to left from right lane closure were choosing to merge early than when they were moving from right lane closure to left lane. This phenomenon cannot be fully justified as the sample size of this study was small. Head to head configuration was associated with drivers merging late. Influence of distraction and cell phone use was seen on drivers’ lane change behavior. When drivers were distracted, the arrowhead CMS sign was not seen to be effective, meaning that the drivers did not choose to merge early in work zones lane closure scenario. Similarly, when they were distracted by cell phone, the normal speed limit signs were not effective to influence the drivers to merge early for a lane closure ahead scenario. Several different analyses were conducted in order to evaluate the data from different perspectives. The different models had different response variables (i.e. change in speed, lane merge distance). The change in speed model assume that a driver decelerating or decreasing speed when they encounter a work zone feature were interpreted as positive behaviors. However, they do not capture drivers who may have slowed their speed entering the work zone and then maintained their speed. As a result, they would not have needed to slow when encountering additional features. For the lane merge analysis, it was assumed that drivers merging earlier that is farther ahead of the activity area were showing safe driving behavior than the drivers merging at the vicinity of the activity area. Overall, this study was successful in identifying active work zones from the RID data and reduce valuable information from the forward videos to evaluate driver behavior in work zones.</p

Safety Edge Crash Modification Factors

This study evaluated the safety impact of the Safety Edge for construction projects in 2010 and 2011 in Iowa to assess the effectiveness of the treatment in reducing crashes.For this and other reports please see the InTrans project page at http://intrans.iastate.edu/research/projects/</p

Safety Evaluation of Stop-Sign Mounted Beacons—A Cross-Sectional Study

Agencies in Iowa have utilized both overhead flashing beacons and stop-sign mounted beacons. Although several studies have shown that overhead flashing beacons are effective, some concerns have been raised about driver confusion. The main concern is that a driver may interpret a multiface flashing beacon with a red indication for their approach as an all-way stop control. As a result, the Iowa DOT has been advocating use of stop-sign mounted beacons rather than overhead flashing beacons. Since little information is available about this countermeasure, data for intersections with (treatment) and without (control) stop-sign mounted beacons were identified and a cross-sectional analysis conducted (due to few confirmable installation dates). Rural stop-controlled intersections with stop-sign mounted beacons in Iowa (USA) were identified (40 in total). Intersection characteristics such as number of approaches, intersection angle etc. were extracted. Additionally, characteristics of individual approaches such as roadway surface (gravel/paved), advanced stop-sign rumble strips, and advance signing were recorded. One or more control locations were manually selected for each treatment intersection based on matching roadway configuration, presence of lighting, advance stop line rumble strips, number of approaches, channelization, traffic volume, and proximity. Propensity scores were estimated to match 40 control locations for comparison. Negative binomial models for different injury combinations at nighttime and daytime were developed with an indicator variable for presence and absence of stop-sign mounted beacons. Presence of stop-sign mounted beacons was associated with a 5% - 54% reduction in nighttime crashes. Injury nighttime crashes decreased by 54% and total nighttime crashes reduced by 18%.This article is published as Goswamy, A. , Hallmark, S. , Basulto-Elias, G. and Pawlovich, M. (2019) Safety Evaluation of Stop-Sign Mounted Beacons—A Cross-Sectional Study. Journal of Transportation Technologies, 9, 95-108. https://doi.org/10.4236/jtts.2019.91006. Posted with permission

Effect of signal timing on vehicles’ near misses at intersections

Abstract Driving characteristics often vary between the different states of the signal. During red and yellow phase, drivers tend to speed up and reduce the following distance which in turn increases the possibility of rear end crashes. Intersection safety, therefore, relies on the correct modelling of signal phasing and timing parameters, and how drivers respond to its changes. This paper aims to identify the relationship between surrogate safety measures and signal phasing. Unmanned aerial vehicle (UAV) video data has been used to study a major intersection. Post encroachment time (PET) between vehicles was calculated from the video data as well as speed, heading and relevant signal timing parameters such as all red time, red clearance time, yellow time, etc. Random parameter ordered logit model was used to model the relationship between PET and signal timing parameters. Overall, the results showed that yellow time and red clearance time is positively related to PETs. The model was also able to identify certain signal phases that could be a potential safety hazard and would need to be retimed by considering the PETs. The odds ratios from the models also indicate that increasing the mean yellow and red clearance times by one second can improve the PET levels by 10% and 3%, respectively