The increasing use of railway trains for the conveyance of the mails has presented new and difficult problems with reference to the authority of the Postmaster-General over mail trains and reasonable payments to the railway companies. So far as the method for ascertaining the rate of payment was concerned, a difficulty arose as to whether the Post Office should pay any part of the tolls as distinguished from operating expenses. Major Harness, a Post Office official, stated that in discussing this question with Robert Stephenson in the case of the London and Birmingham Railway it had been agreed that tollage should not be paid but only the out-of-pocket expenses, this being in conformity with the principles adopted in paying for mail coaches. The question of tollage was not mentioned by the Railway Mails Act (10 and 11 Vict., c. 85), but Major Harness, in his evidence before a parliamentary committee, stated that he, as an arbitrator, estimated the tollage payable by the Post Office by finding out how much each ton, if the road were fully occupied, should contribute to return 10 per cent upon the share capital and 5 per cent on the bonds, the Post Office to pay its proportion according to the weight of mail matter carried. The cost of locomotive power was also taken into count and the carriage accommodation was paid for on the basis of what the railways charged each other.[304] In addition to these items the committee recommended that the expenses for station accommodation, the additional cost of the working staff, and interference with ordinary traffic should also be taken into account.[305] In the event of a failure on the part of the Post Office and a railway company to come to an agreement as to the amount payable, each of the parties nominated an arbitrator whose first duty was to select an umpire. Each arbitrator was required to present his case in writing to the umpire and to attend in person if required. The umpire was supposed to give his decision within twenty-eight days after the receipt of the cases.[306] In 1893 it was provided by act of Parliament that when any dispute arose between the Post Office and a railway, the question should be taken to the Railway and Canal Commission for settlement instead of being left to arbitration.[307] The Postmaster-General has also been authorized to make use of tramways for transporting the mails, and in 1897 the experiment was made of using motor vans for the same purpose. A few years later the Postmaster-General expressed himself as "doubtful whether a thoroughly reliable motor vehicle suitable for Post Office work has yet been found." However, in 1906-07 about thirty-five mail services were performed by motors, the work being undertaken by contractors who provide the vans and employ the drivers. They have proved to be more economical than horse vans when the load is heavy, the distance considerable, and greater speed desirable.[308] [304] _Rep. Com._, 1854, xi, 411, pp. 370-371.