The greatest single challenge facing Rowland Hill and his supporters, and there were numerous difficulties to be overcome, was the increase in volume of traffic. As mentioned previously, the amount of mail carried in the pre 1840 era was very small by mid Victorian standards, and Hill had the foresight to recognise the difficulties ahead.
The sudden influx of mail into offices in large cities and towns during the evening postings had to be dealt with quickly. Delays to the mail would have meant an opportunity for Hill's critics to carp about what it was he was trying to achieve. The innovator of the scheme was having none of this and had decided that speedy and efficient mail sorting and distribution, was to be a key part of his plan. To this end Hill and/or others had the good sense and foresight to see how the mail could be best dealt with.
No longer would it be possible or sensible to have large numbers of road coaches careering out of London during the evening. Instead, the mail would be conveyed to one of the new railway stations from which it could be loaded into a train and sent on to various destinations along the line. However, this was not to be enough, so great was the influx of mail into the sorting offices that more revolutionary strategies had to be employed.
This brought the minds of those Victorian Post Office innovators to bear on the question of how to deal with the increasing flow of traffic. Their solution to the problem was to get it out of the sorting offices as quickly as possible, and on to a Traveling Post Office (TPO) in an unsorted state. It is worth noting that the first experiments with TPO's took place in January 1838, almost two years before the introduction of the uniform penny post! Hill and his associates were able to anticipate the problems that lay ahead. These new TPO's, also called Railway Post Offices or Moving Post Offices became the key to the success of the uniform penny post. It was the Internet of the 1840's.
The methodology behind sorting systems is quite complicated and would not be best described here. Suffice to say that once the mail was received into a receiving (later sorting) office, it would be sorted into areas of the country (primary sorting) and would then be transferred to the railway system.
As the railway systems grew so the road coaches diminished and the use of TPO's and Sorting Carriages (SC) became more evident across the network. With London being the principal city as well as being the largest it had always been the hub of all postal activities. The railways too, soon found their way to London and radiated out from the capital roughly following the old major coaching routes. Lines to Dover, Plymouth, Penzance, Bristol, Cardiff, Holyhead, Birmingham, Crewe, Glasgow, Edinburgh, Newcastle, Sheffield, Derby, York and Norwich, were all accessible from London. The various TPO's and SC's adopted names suited to their location and lines of railway companies over which they traveled. The "North Eastern", "North Western", "Great Western", "South Eastern", "Great Northern", "Caledonian" and "East Anglian" were all names used over the years at various times and gave some indication of the routes they traveled. District Sorting Carriages tended to be named after the places from which they were staffed and ran from/to. Typical were the Glasgow, Edinburgh, Ipswich and Cambridge SC's.