What you are talking about is the so-called "Solomon Curve". This if oft-quoted research which seems to show that slower moving drivers in a rural highway type situation have far more crashes than those driving with the flow of traffic and even those driving a fair bit faster than average.

There are three basic problems with this, however:

- It is research on rural highway and freeway type situations that applies only that that particular situation. We might all agree that driving 25 mph on an 80 mph freeway is best to be avoided, if you can. But it has literally no application to streets and roads in a town or city - that's not where any of the data behind the Solomon Curve came from.

- The researchers did not separate out turning situations from the "slow driver" situation, which is the one we are talking about here. Turning and crossing movements are disproportionately represented in rural highway crashes - people are usually going quite slow during turns.

It's the turning part that increases the risk of collisions, though - not the slow speed. Solomon massively skewed his research by including all these turning drivers and classifying them as "slow drivers".

- More recent and careful research has rather definitely overturned the "Solomon Curve".

Here is decent research summary that makes all the same basic points I did in my two comments above, but backs them with citations and evidence, and also tackles the Solomon Curve "are slow drivers dangerous?" issue:

https://safety.fhwa.dot.gov/speedmgt/ref_mats/fhwasa1304/Resources3/08%20-%20The%20Relation%20Between%20Speed%20and%20Crashes.pdf

Regarding the supposed high crash risk of slow driving, it says:

>The first studies of this type were conducted in the United States in the 1950s and 1960s, e.g. Solomon (1964). These studies always found a U-curve: the slower or faster a car drives compared with most of the vehicles on that road, the more the risk of being involved in a crash increased.
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>However, more recent studies, especially those carried out in Australia (e.g. Kloeden et al., 1997; 2001; 2002) that used more modern measuring instruments and used a more accurate research design, reached a different conclusion. They still indicate that vehicles that drive faster than average on that road have a higher crash rate; vehicles that drive slower, however, were found not to have an increased risk (Figure 3).

Figure 3 is worth taking a look at. For rural roads, it shows:

- Slightly lower crash risk for those traveling slower than average.

- Slightly higher crash risk for those traveling faster than average

For urban roads, the situation is somewhat different:

- Still slightly lower crash risk for those traveling slower than average.

- However, massively higher crash risk for those traveling much faster than average.

If you're going say 5mph faster than average, the crash risk just just a bit higher - about what you'd expect.

But drive 10-15 mph faster than the average speed and now we're talking 10X-30X increased crash risk.