The Hidden Danger of Driving Too Slowly: What the Solomon Curve Teaches Us About Road Safety
When we think of risky driving, our minds often jump straight to speeding. Yet, driving significantly slower than surrounding traffic can be just as dangerous, if not more so. This counterintuitive fact has been backed by research dating back to the 1960s, most notably through the work of traffic safety researcher David Solomon.
What is the Solomon Curve?
In his seminal study, Solomon analysed over 10,000 crashes on rural highways and found a clear U-shaped relationship between vehicle speed and crash involvement rates. This became known as the Solomon Curve.
The findings were striking:
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Vehicles travelling much faster or much slower than the average speed of traffic were far more likely to be involved in collisions.
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The safest speeds were those slightly above the average traffic speed, not below it.
Why Driving Slowly Can Be Dangerous
Driving considerably below the speed limit or the flow of traffic can disrupt the natural rhythm of the road. This disruption can:
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Force other drivers into sudden braking or unnecessary lane changes.
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Cause congestion and “shockwave” traffic patterns.
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Lead to rear-end collisions, especially on high-speed roads where drivers may not anticipate a slower vehicle.
Simply put, speed differentials, the gap between your speed and that of surrounding vehicles, are a major factor in crash likelihood.
What the Research Says
Solomon’s research has been supported by subsequent studies over the decades, including:
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Cirillo’s 1968 study confirmed the U-shaped crash curve on interstate highways.
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Reports by the Federal Highway Administration (FHWA), which acknowledged that both excessive speed and slow driving can be hazardous.
These findings remain especially relevant on motorways, A-roads, and dual carriageways, where slower drivers can become moving obstacles.
The Safer Strategy: Match the Flow
While it’s crucial to obey posted speed limits, it’s equally important to maintain a speed consistent with traffic flow, conditions permitting. Doing so:
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Reduces lane-switching and erratic behaviour by other drivers.
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Keeps traffic moving more smoothly and predictably.
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Minimises your exposure to sudden hazards.
A Word of Caution
This doesn’t mean you should speed to keep up; safety always comes first. But if you’re travelling well below the limit without a clear reason (e.g. roadworks, poor weather, a mechanical issue), you may be inadvertently increasing your risk of being in a crash
Driving too slowly, particularly on fast-moving roads, can be just as risky as speeding. The Solomon Curve reminds us that traffic safety isn’t just about absolute speed but relative speed. Stay alert, go with the flow, and always drive to the conditions.