Investigation of Clearance Criterion Between Tether Anchor and Head Restraint

Abstract

In response to questions about the proposed vehicle clearance criterion of 165 mm between the back of the head restraint on the vehicle seat and the vehicle tether anchor that would allow proper tightening of the child restraint tether strap, this project aimed to estimate how many vehicles already meet this criterion, document physical features that prevent compliance, determine an alternative criterion that is more repeatable to measure, and to check for conflicts between a new criterion and other regulations or practices. Analysis of several existing UMTRI data sets, as well as new in-vehicle measurements were employed. This study does not account for new trends in placement of tether anchors and the methods were insufficient to evaluate anchors in the pick up trucks in the current data sets. The data show that about 75% of vehicle models evaluated (including all those with tether anchor hardware on the seatback) already meet the criterion. Changing the tether routing from under to over the head restraint would provide improved access to tether adjustor hardware in most vehicles, and might be considered as an alternative option to a tether clearance criterion. For vehicles with obstructive hardware, speakers are the most common element in conflict. A new criterion based on the R-point of the seating position with similar effectiveness is proposed. This new metric does not conflict with those of the Australian Design Rule, Society of Automotive Engineers or Insurance institute for Highway Safety.