Speeding attracts most of the attention, but it is not the only way to become a hazard. Research has long shown that driving significantly slower than surrounding traffic can increase crash risk just as sharply.
One of the earliest and most cited findings comes from the US Federal Highway Administration’s work on speed variance, often referred to as the Solomon Curve. It showed that vehicles travelling well below the average traffic speed were involved in more collisions than those moving with the flow, even when all were within legal limits.
More recently, the AAA Foundation for Traffic Safety has reinforced this conclusion. Its studies highlight speed differentials as a key factor in rear end and lane change crashes, particularly on multi lane highways where drivers expect consistent movement rather than sudden obstacles.
The problem is not slowness itself but unpredictability. Traffic works as a system. When one vehicle is moving 10 mph or more slower than the prevailing flow, other drivers are forced into late braking, abrupt steering inputs or rushed overtakes. Each reaction increases the chance of a mistake, and those mistakes rarely remain isolated.
European research echoes the same point. Data from Germany’s Federal Highway Research Institute shows that large variations in speed within traffic streams significantly raise accident rates, even on roads with strict speed discipline.
This does not mean speed limits are optional. It means safe driving sits between blind obedience to a number and reckless pace. The safest drivers adjust to conditions while remaining legal, predictable and visible to others.
Road safety is not just about how fast you are going. It is about how well your speed fits the environment around you. Consistency is what keeps traffic moving and accidents down.