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In this study, experimental methods were used to compare the consequences of employing snubbing versus dragging strategies to control the speeds of trucks on downgrades. Vehicle tests were performed on a long steep grade. A mobile dynamometer was used to study cooling rates and hot spotting. The basic findings of the study are: (1) the average temperature per pound (kilogram) of brake drum is practically equivalent whether light dragging or snubbing is used; (2) the hottest brakes will be cooler if snubbing is used; and(3) on short downhill descents, the dragging strategy will cause hot spots to develop to a greater extent. For many years there has been controversy between those that recommend dragging brakes versus those that recommend snubbing (pulsing) to control vehicle speed during downhill descents. Recently, interest in commercial driver licensing (CDL) has stimulated discussions of the merits of these two braking strategies.

This paper focuses on two types of electronics-based object detection systems for heavy truck applications: those sensing the presence of objects to the rear of the vehicle, and those sensing the presence of objects on the right side of the vehicle. The rearward sensing systems are intended to aid drivers when backing their vehicles, typically at very low “crawl” speeds. Six rear object detection systems that were commercially available at the time that this study was initiated were evaluated. The right side looking systems are intended primarily as supplements to side view mirror systems and as an aid for detecting the presence of adjacent vehicles when making lane changes or merging maneuvers. Four side systems, two commercially available systems and two prototypes, were evaluated.

A Supplemental Notice of Proposed Rulemaking (SNPRM, Notice 4) for FMVSS 135 has recently been issued proposing a new braking regulation for passenger cars. Due to interest in light truck braking performance as it relates to that of passenger cars, a sample of 13 light trucks was tested to the FMVSS 135 Notice 4 procedure for purposes of comparison with the performance of a sample of 19 passenger cars tested to the same procedure. The brake force balance and braking efficiency of the light trucks were also measured and compared to the same parameters of the set of 19 cars.

This paper addresses the issue of front wheel braking on heavy trucks and reviews testing that has been performed over the years dating back to 1948 to evaluate the effect of front brakes on braking performance. It also describes in detail a test and demonstration program on front wheel brakes that was conducted in September 1986. The paper indicates that front wheel brakes have a strong effect on braking performance and that vehicles without front wheel brakes take longer distances to stop and are more likely to lose control in emergency situations. The paper also indicates that the use of front brake pressure limiting valves with typical, current design front brakes degrades vehicle braking performance.