The Mt. Vernon (New York) Fire Department (below) was paying out $36 per fire engine for horse upkeep. The Knox road tractors that replaced them cost $2 each per month.
Knox's introduction in 1915 of their Model 35 tractor with four wheels put and end to the three-wheeler.
thanks to Steve http://serviside.blogspot.com/2011/09/tugboat-of-land-commerce.html who still has to add this info to HIS post!
He is kinda busy, but reads my blog, and when I post something I know nothing about, he blows my mind with his deep knowledge of it.. this post is due to the photo I put up yesterday:
the Knox Martin Tractor was introduced at least by 1911, and was built at least through 1914. Its inventor, Charles H. Martin was acknowledged to be the father of the semi-trailer, having invented (and commercially applied it to the Knox) the rocking fifth-wheel that is still in use today - along with the term "tractor-trailer." In 1911 Martin opened his own factory to build Martin Tractors, while advertising that only the Knox and Martin were licensees of Martin patents.
above image only, found on http://truquetructruk.tumblr.com/