General Knowledge · Controlling Speed
Why can a loaded truck roll over on a curve even while traveling at or below the speed posted on a curve warning sign?
Explanation
A loaded commercial vehicle can roll over on a curve even at or below the posted speed because that speed is set based on a passenger car's lower center of gravity, not a truck's higher one, so a speed that is safe for a car can still be too fast for a top-heavy truck. Adjusting speed for the shape of the road is part of the required knowledge CDL applicants must have under 49 CFR 383.111(a)(9)(iii), but that paragraph only names "speed and the shape of the road" as a required knowledge topic; it does not itself state this rollover-risk fact, which is standard driver-training content rather than a codified federal rule. The other options fail for a shared reason: each invents a limitation or a different purpose for curve speed signage that does not exist, whether restricting it to towing vehicles, redefining what it measures, or confining it to work zones.
Source: 49 CFR 383.111(a)(9)(iii)
Related Controlling Speed questions
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