Cody S Stolle

Guidelines for Implementation of Cable Median Barrier

A detailed examination of accidents in Kansas evaluated the need for a cable median barrier. Hard copies of all accident reports from Kansas controlled-access freeways from 2002 to 2006 were reviewed. A total of 525 cross-median events and 115 cross-median crashes were identified. Cross-median encroachment rates were linearly related to traffic volume and cross-median crash rates appeared to have a second-order relationship to volume. Cross-median crashes were much more frequent in winter months and the severity of wintertime crashes was lower. This finding indicates that median barrier warranting criteria may need to be adjusted to accommodate regional climate differences, especially for warranting guidelines based on cross-median crash rates. A relationship was found between cross-median crash rate and traffic volume for Kansas freeways with median widths of 60 ft (18.3 m). This relationship was combined with encroachment rate and lateral extent of encroachment data from the Roadside Safety Analysis Program to develop general guidelines on the use of cable median barriers along Kansas freeways.

Development of a wire rope model for cable guardrail simulation

Cable guardrail systems have received increased attention due to their low installation cost and excellent safety performance. This has led to an increase in the use of non-linear finite element modelling for the design and analysis of such systems. However, wire rope models previously used were not validated with physical testing. Thus, an improved non-linear finite element analysis model of 19-mm diameter 3 × 7 wire rope commonly used in roadside cable guardrail installations was developed. Component tests were conducted on wire rope, and consisted of quasi-static tension and cantilever bending tests, high-speed jerk tests of wire rope constrained at one end and perpendicular impacts of wire rope constrained at both ends. Simulation of these tests indicated favourable comparison of bogie vehicle motion and wire rope tension with test results, and was significantly more accurate than previously developed models. Application of the new wire rope model to a full-scale impact on a cable guardrail system indicated good comparison of the new wire rope model with the wire rope reactions in the full-scale test.

Roadway Departure and Impact Conditions

In-depth accident data were collected to investigate vehicle impact conditions (e.g., crash severity, impact speed, impact angle, and orientation) for crashes with roadside obstacles and features. Descriptive statistics of these variables are presented, including statistics for the data segregated by highway class, speed limit, and access control. Relationships between impact conditions and these segregating factors were explored. Statistical tests were applied to investigate the association between speed and angle, and univariate distributions were fitted for these two variables. Impact speed and impact angle are independent for most highway classes when segregated by highway class, and they have a relatively weak negative correlation. Both impact speed and angle data for all highway classes follow a normal distribution. Joint impact distributions were then determined using the bivariate normal distribution. The findings of this study are of significant importance to the establishment or reinforcement of full-scale vehicle crash testing guidelines, to benefit–cost analysis procedures, and to highway designers who seek more detailed information on probabilities of impact conditions for different highway classes.

Vehicle-to-barrier communication during real-world vehicle crash tests

Vehicle-to-barrier (V2B) communication is a recently introduced vehicular communication technology, which aims to facilitate wireless interactions between vehicles and roadside barriers in next-generation vehicular systems. V2B systems will help mitigate single-vehicle, run-off-road (RoR) crashes, which account for a large proportion of roadside crash fatalities. RoR crashes may not be addressed by existing vehicular communication systems, such as vehicle-to-vehicle and vehicle-to-infrastructure. Today, orthogonal frequency division multiplexing (OFDM) is vastly utilized in vehicular communication systems. Thus, there is a need to understand the signal characteristics of the channel, especially just before and during a crash. To this end, the first real-world crash test measurement results for OFDM-based V2B communications are presented herein based on two crash tests. These tests include a bogie vehicle crash test into a soil embedded post at an impact velocity of 27 mph and a Toyota sedan crash test into a concrete curb with an impact velocity of 15 mph, conducted at the outdoor proving grounds of Midwest Roadside Safety Facility (MwRSF), Lincoln, Nebraska. Experiment results illustrate the characteristics of V2B OFDM communication during vehicle encroachment and crash. The results highlight the adverse effects of vehicle encroachment and crash on OFDM signals, in terms of average received signal strength, peak to average power ratio, error vector magnitude, and phase error.

Dynamic strength of a modified W-beam BCT trailing-end termination system

W-beam systems utilise end-terminal anchorages to develop tension upstream and downstream of an impact event. However, the capacities of the anchorage components under impact loading are not well known. One such W-beam end-anchorage system, the Midwest guardrail system (MGS) trailing-end anchorage, was evaluated using three dynamic component tests – a soil foundation tube pull test, a breakaway cable terminal (BCT) post splitting test, and an MGS end-anchorage system pull test. The peak load recorded during a soil foundation tube test was 193 kN at 56 mm deflection, as measured at the ground line. BCT posts split at loads of 17.8 and 32.9 kN. The end-anchorage tensile capacity was 156 kN, dissipating 64.7 kJ. Results from the component tests were also used to create and validate nonlinear finite element models of the components in order to be used for future design and analysis of end anchorages.

Rail height effects on safety performance of Midwest Guardrail System

ABSTRACT Objective: Guardrail heights play a crucial role in the way that errant vehicles interact with roadside barriers. Low rail heights increase the propensity of vehicle rollover and override, whereas excessively tall rails promote underride. Further, rail mounting heights and post embedment depths may be altered by variations in roadside terrain. An increased guardrail height may be desirable to accommodate construction tolerances, soil erosion, frost heave, and future roadway overlays. This study aimed to investigate and identify a maximum safe installation height for the Midwest Guardrail System that would be robust and remain crashworthy before and after pavement overlays. Methods: A research investigation was performed to evaluate the safety performance of increased mounting heights for the standard 787-mm (31-in.)-tall Midwest Guardrail System (MGS) through crash testing and computer simulation. Two full-scale crash tests with small passenger cars were performed on the MGS with top-rail mounting heights of 864 and 914 mm (34 and 36 in.). Test results were then used to calibrate computer simulation models. Results: In the first test, a small car impacted the MGS with 864-mm (34-in.) rail height at 102 km/h (63.6 mph) and 25.0° and was successfully redirected. In the second test, another small car impacted the MGS with a 914-mm (36-in.) rail height at 103 km/h (64.1 mph) and 25.6° and was successful. Both system heights satisfied the Manual for Assessing Safety Hardware (MASH) Test Level 3 (TL-3) evaluation criteria. Test results were then used to calibrate computer simulation models. A mounting height of 36 in. was determined to be the maximum guardrail height that would safely contain and redirect small car vehicles. Simulations confirmed that taller guardrail heights (i.e., 37 in.) would likely result in small car underride. In addition, simulation results indicated that passenger vehicle models were successfully contained by the 34- and 36-in.-tall MGS installed on approach slopes as steep as 6:1. Conclusions: A mounting height of 914 mm (36 in.) was determined to be the maximum guardrail height that would safely contain and redirect 1100C vehicles and not allow underride or excessive vehicle snag on support posts. Recommendations were also provided regarding the safety performance of the MGS with increased height.

Optimal guardrail runout lengths for freeways

ABSTRACT Guardrails have commonly been installed to prevent errant vehicles from impacting roadside hazards. However, guardrail impacts have contributed to numerous serious injuries and fatalities. Plus, guardrails are generally impacted more often because they are installed closer to the edge of travel way and are much longer than the shielded hazard itself. Thus, to reduce the frequency of guardrail crashes, an optimized length should be determined. The American Association of State Highway and Transportation Officials (AASHTO) Roadside Design Guide (RDG) has suggested guardrail runout lengths which are dependent on posted speed limit and traffic volumes. Crash data analyses and simulation using the recently-updated Roadside Safety Analysis Program (RSAPv3) was conducted to evaluate the guardrail length-of-need (LON) associated with the lowest crash cost (i.e., cost associated with injuries and property damage) and maximum cost-effectiveness for freeways. Crash data involving Kansas guardrail systems, which were compliant with recommendations provided in the 2006 AASHTO RDG and occurring on freeways with divided medians, were collected and analyzed. The frequency, rate, and risk of shielded hazard crashes were extremely low. RSAPv3 analyses indicated that there was an economic and safety benefit to reducing the installed LON as well as utilizing different runout lengths for left- and right-side departures for divided roadways.

Cost-Effective Safety Treatment of Trees on Low-Volume Rural Roads

Generally, trees are naturally occurring fixed objects that are found along many roadways and that potentially pose safety risks to errant motorists. Unfortunately, trees have been responsible for numerous fatal and serious injury crashes during run-off-road events. This study included an incremental benefit-to-cost (B-C) analysis that used the Roadside Safety Analysis Program to investigate the efficacy of safety treatment alternatives for trees on roadways with volumes of less than 500 vehicles per day (vpd) and speed limits of 55 mph (88.5 km/h) or greater. The study was based on a parametric analysis of site characteristics from a field survey in Kansas. It used four tree groupings, three tree diameters, and four lateral offsets from the roadway to configure 120 scenarios. Three safety treatment methods were considered: (a) a do-nothing option representing the baseline condition; (b) tree removal, with cost estimates coming from reliable sources; and (c) a crashworthy guardrail system. For various reasons, the guardrail system was no more cost-effective than the do-nothing or tree removal options. B-C ratios were used to recommend tree removal on the basis of several pertinent variables. In all cases, B-C ratios for tree removal were never less than 1.0, which indicated limited justification for keeping the trees. Tree removal was considered the safest and primary alternative when trees were far from other fixed obstacles. Because these guidelines are based solely on B-C analyses, the road designer or engineer is encouraged to use them as a foundation for making safety improvements but also to consider site-specific investigation and analysis.