Expansion of NASS/CDS for characterizing run-off-road crashes

Abstract

Objective: Runoff road (ROR) crashes account for one-third of all annual crash fatalities in the US. The National Automotive Sampling System Crashworthiness Data System (NASS/CDS) is a dataset which may be used to understand the nature of ROR crashes. Despite the wealth of coded data available in NASS/CDS, this dataset lacks coded information about the roadside environment and the off-road trajectory of the vehicle. This information would be useful for determining lane departure warning (LDW) benefits, residual safety problems, performance of current safety hardware, lane marking inventory, LDW test procedure development, radius of curvature characterization, and effectiveness of ESC. The purpose of this paper is to demonstrate a methodology for expanding the data available in NASS/CDS to form and validate a specialized road departure database. Methods: Observed, measured, and reconstructed data elements were extracted from NASS/CDS and compiled into the National Cooperative Highway Research Program (NCHRP) 17-43 database. Observed variables were primarily coded from the scene photographs and included information such as the lane markings, and geometry of the roadside cross-section. Additional variables were measured from the scaled scene diagrams including the path of the vehicle, road dimensions, and roadside object positions. The vehicle impact speed and departure speed were reconstructed using the WinSMASH delta-v, roadside object characteristics, and vehicle path. Two studies were conducted to demonstrate the usefulness of the NCHRP 17-43 database in evaluating both vehicle-based and infrastructure-based ROR countermeasures. Results: The resulting NCHRP 17-43 database includes 1,581 NASS/CDS cases representing 510,154 ROR crashes. Analysis of the database found that drivers which crashed following an overcorrection were younger than drivers which did not overcorrect. This may indicate that inexperienced drivers are more likely to overcorrect when departing the roadway. The 85 th percentile impact severity of ROR crashes, which occur on roads with a speed limit greater than 65 mph, is higher than the practical worst-case test conditions for roadside barriers. Conclusions: The NCHRP 17-43 database contains information extracted from NASS/CDS cases to better understand the nature of ROR crashes, driver behavior in these crashes, and the potential benefits of both vehicle-based and infrastructure-based ROR countermeasures.

Corridor-Based Procedure for Determining Longitudinal Barrier Length of Need

“…NASS/CDS provides detailed data on vehicles and occupant injuries but contains very little information on the roadside or roadside hardware. NCHRP 17-43 data augment the NASS/CDS data by providing coded roadside information ( 13 ). Each crash in the NASS/CDS has a case weight that, when applied to the entire dataset, makes the results nationally representative.…”

“…Each crash in the NASS/CDS has a case weight that, when applied to the entire dataset, makes the results nationally representative. The impact speed and departure speed of the NCHRP 17-43 cases were reconstructed utilizing the delta-v computed by NHTSA with the WinSMASH software and an energy-based methodology ( 13, 25 ).…”

“…A braking magnitude of 0.41 g was utilized, which is the average braking magnitude for drivers in road departure crashes observed in event data recorder data ( 27 ). The extrapolated trajectory terminated where the dissipated kinetic energy was equivalent to the energy before the original impact (Equation 1) ( 13 ). If the change in velocity resulting from braking during the extrapolated trajectory was greater than the original impact speed, then the vehicle came to a stop.…”

“…More recent road departure studies, such as NCHRP 17-22 ( 8 ) and NCHRP 17-43 ( 13 ), have full two-dimensional trajectory data. The encroachment trajectory is important to consider for the optimization of barrier LON (Figure 2).…”

Properties of Encroachments and the Associated Roadway and Roadside Environment in the Second Strategic Highway Research Program

“…The National Cooperative Highway Research Program (NCHRP) 247 used crash data along similar lengths of roadway to estimate encroachment modification factors for clear zones (11). This in-depth crash data collection for the improvement of roadside design has been completed in Europe (12,13) and in the U.S. (14,15). These datasets are incredibly useful but, by nature, they can only contain encroachments that resulted in a crash.…”