It is my understanding that one of the questions asked in the 1860 US census was the number of runaway slaves.

That less than 2,000 slaves were reported as runaway in that census. That is a factor of .0000003% of the slave population as reported. Everybody seems to discount this because it doesn't fit what we have been taught to believe. But it is the only "official" record of the subject that I know of.

Admittedly, this would seem an extremely low percentage considering the number of slaves in "borber states" where it would be realitively simple to reach a safe house. And even Texas which a slave could run to Mexico. On the other hand as valuable as slaves were it would seem that a better accounting of lost "property" would have been kept, IF the problem was as widespread as the conventional wisdom would suggest.

Therefore, I believe that the 50,000 runaways a years, which is still less than 2% of the slave population a year, is an over estimation of the situation. Neither the underground railroad, nor the Northern populas would have been able to absorb that many runaways. So in logical evaluation there were physical limits which in themselves argue against numbers of runaways higher than 1/2 of 1 percent as being illogical.

A second element is, how long did a slave have to be gone before he was considered a runaway? There are many letters of soldiers who used slaves to bring them clothes and send things home by them. And I have not heard of any of those slaves traveling under the supervision of an armed guard. Also the Confederate army contracted for the services of plantation slaves, who watched them? I don't think the army had the manpower to assigne a soldier to watch over every 20 slaves all the time.