S Doecke

The real-world safety potential of connected vehicle technology.

Objective: This article estimates the safety potential of a current commercially available connected vehicle technology in real-world crashes. Method: Data from the Centre for Automotive Safety Researchs at-scene in-depth crash investigations in South Australia were used to simulate the circumstances of real-world crashes. A total of 89 crashes were selected for inclusion in the study. The crashes were selected as representative of the most prevalent crash types for injury or fatal crashes and had potential to be mitigated by connected vehicle technology. The trajectory, speeds, braking, and impact configuration of the selected in-depth cases were replicated in a software package and converted to a file format allowing “replay” of the scenario in real time as input to 2 Cohda Wireless MK2 onboard units. The Cohda Wireless onboard units are a mature connected vehicle technology that has been used in both the German simTD field trial and the U.S. Department of Transports Safety Pilot project and have been tuned for low false alarm rates when used in the real world. The crash replay was achieved by replacing each of the onboard unit Global Positioning System (GPS) inputs with the simulated data of each of the involved vehicles. The time at which the Cohda Wireless threat detection software issued an elevated warning was used to calculate a new impact speed using 3 different reaction scenarios and 2 levels of braking. Results: It was found that between 37 and 86% of the simulated crashes could be avoided, with highest percentage due a fully autonomous system braking at 0.7 g. The same system also reduced the impact speed relative to the actual crash in all cases. Even when a human reaction time of 1.2 s and moderate braking of 0.4 g was assumed, the impact speed was reduced in 78% of the crashes. Crash types that proved difficult for the threat detection engine were head-on crashes where the approach angle was low and right turn–opposite crashes. Conclusions: These results indicate that connected vehicle technology can be greatly beneficial in real-world crash scenarios and that this benefit would be maximized by having the vehicle intervene autonomously with heavy braking. The crash types that proved difficult for the connected vehicle technology could be better addressed if controller area network (CAN) information is available, such as steering wheel angle, so that driver intent can be inferred sooner. More accurate positioning in the real world (e.g., combining satellite positioning and accelerometer data) would allow the technology to be more effective for near-collinear head-on and rear-end crashes, because the low approach angles that are common in such crashes are currently ignored in order to minimize false alarms due to positioning uncertainty.

An Analysis of Head Impact Severity in Simulations of Collisions Between Pedestrians and SUVs/Work Utility Vehicles, and Sedans

Objective: To describe the determinants of the severity of the head kinematics of a pedestrian when struck by common sport utility vehicles (SUV) and work utility vehicles (WUVs) to assess how effective assessment protocols are in assessing injury risk for SUVs and work utilities. Methods: Three hundred twenty-four simulations of pedestrian collisions with SUVs, work utility vehicles, and sedans were performed using several vehicle geometries, pedestrian orientations, speeds, and braking levels. Contact stiffnesses in the models were based on impact test results with exemplar vehicle structures. A single contact characteristic was used for all head-to-hood contacts to allow the effects of other factors on head injury risk to be compared. Simulations of standard headform tests on the same hood characterized the structure from a subsystem test perspective. Results: Head injury criterion values were higher in SUV/WUV simulations than sedan simulations because of high neck tension rather than through higher contact forces with the hood. In fact, the severity of the impact between the head and hood was slightly less in SUV/WUV simulations. Sedan and SUV/WUV simulations produced lower head injury criterion (HIC) values than did the subsystem tests. Conclusions: High bonnet leading edges led to increased neck loads in these simulations of pedestrian collisions. Neck loads were influential on head injury risk in the SUV/work utility simulations but not in sedan simulations. Subsystem impact tests may overestimate head impact risk from the hood itself but fail to capture a potentially important injury mechanism in collisions with vehicles with high leading edges and thus fail to differentiate completely risks posed by such vehicles. These results may have implications for the interpretation of pedestrian subsystem test results: a given HIC value in an SUV/WUV test may represent a relatively higher risk of injury than the same results recorded in a sedan test.

Safe speed limits for a safe system: The relationship between speed limit and fatal crash rate for different crash types

ABSTRACT Objective: The objective of this article is to provide empirical evidence for safe speed limits that will meet the objectives of the Safe System by examining the relationship between speed limit and injury severity for different crash types, using police-reported crash data. Method: Police-reported crashes from 2 Australian jurisdictions were used to calculate a fatal crash rate by speed limit and crash type. Example safe speed limits were defined using threshold risk levels. Results: A positive exponential relationship between speed limit and fatality rate was found. For an example fatality rate threshold of 1 in 100 crashes it was found that safe speed limits are 40 km/h for pedestrian crashes; 50 km/h for head-on crashes; 60 km/h for hit fixed object crashes; 80 km/h for right angle, right turn, and left road/rollover crashes; and 110 km/h or more for rear-end crashes. Conclusions: The positive exponential relationship between speed limit and fatal crash rate is consistent with prior research into speed and crash risk. The results indicate that speed zones of 100 km/h or more only meet the objectives of the Safe System, with regard to fatal crashes, where all crash types except rear-end crashes are exceedingly rare, such as on a high standard restricted access highway with a safe roadside design.