Considering real-world sightline obstructions in crash and injury prevention estimates for left turn across...

Previous analyses of active safety systems in left turn across path/opposite direction (LTAP/OD) crashes have shown that sensor sightline obstructions might affect the performance of these systems. National retrospective crash databases provide little information about the proportion of cases which have sightline obstructions. One promising alternative are naturalistic driving studies (NDS). The objective of this study was to estimate the proportion of LTAP/OD crashes and near-crashes which have sightline obstructions using a large-scale NDS and update previous estimates of intersection active safety system effectiveness using this information.

LTAP/OD crash and near-crash cases were identified from the Second Strategic Highway Research Program (SHRP 2) dataset. Each case was reviewed for the presence of obstructing vehicles when the left turning vehicle began turning. This study considered 241 crash and near-crash LTAP/OD events selected from SHRP 2. SHRP 2 was an NDS which collected 80 million kilometers of driving from approximately 2,500 participants over a 2.5 year period. The sightline obstruction ratio was defined as the proportion of cases which had sightline obstructions when the turning vehicle began turning. A logistic regression model was used to determine the statistical significance of factors which affected the sightline obstruction ratio, which included event severity, traffic control device, subject vehicle crash configuration, and turning lane presence. LTAP/OD active safety system effectiveness was quantified in a prior study for cases with and without sightline obstructions separately. System effectiveness was re-computed by weighting the results according to the worst-case sightline ratio computed in this study.

Traffic control device, subject vehicle crash type (turning or traveling through), and turning lane presence were not found to affect sightline obstruction ratio. In crash cases, the sightline obstruction ratio was 40%. In near-crash cases, the sightline obstruction ratio was 18%. Finally, the effectiveness of an intersection active safety system was evaluated using this sightline obstruction ratio.

This study quantified the sightline obstruction ratio, an important parameter needed to evaluate intersection active safety systems. This study also establishes a baseline for evaluating the presence of sightline obstructions in a future naturalistic driving study when road infrastructure has changed.