Abstract: The most common “critical reason” (22.3%) for single-vehicle large truck crashes is “too fast for curve/turn” which leads directly to rollovers and skids. Manual Inclinometer System(s) (MIS) can provide an extremely inexpensive and reliable heads-up visual warning to drivers when their vehicle is going too fast for any (dry) curve or turn, and thereby prompt them to slow down before it is too late. Approximately 15,000 large truck rollovers occur in the U.S. each year, and as many as 4,000 of these crashes may be preventable using MIS. When the relative lateral acceleration of any “too fast for curve/turn” condition exceeds a preset threshold, then the MIS unit can also (optionally) latch-up in order to provide a warning to fleet safety managers and/or law enforcement that a driver is at high risk for having a preventable rollover crash.