It would be difficult to form an opinion as to how far passenger traffic will go on expanding, but if it continues to increase at the same rate as at present, some railways may find it expedient, and even absolutely necessary, to construct new lines altogether separate and apart from the existing routes, and for the sole use of their fast through traffic. As roadside or intermediate traffic would not form any part of the scheme, such lines could be laid out so as to keep away from the populous districts, where property would be costly, and pass instead through those parts of the open country where the most direct course and easiest gradients could be obtained. Stations would only be required at the very large and important places, and at long distances from each other. Lines of this description, reserved for through traffic only, taken alone, might not pay, but taken in conjunction with the existing lines, of which they would form a part, they might prove to be the best solution of the problem of dealing with a crowded train service, the remunerative earnings of which, placed together, might yield a rich return over the entire system. A project for a separate through line might at first appear a little startling, but we have well-known precedents in the vast expenditure already incurred in the constructing of enormous viaducts and connecting lines to avoid long detours on certain through routes. The widening out of an ordinary double line into a four-line road was at first considered as a rather venturesome departure; and it must always be costly because, in addition to the earthworks and permanent way, there is the doubling of all the over and under bridges and waterways, besides the great and expensive alterations at stations. Practically it is almost like making a second railway, and yet the constant extension of the principle is an admission that the working results have proved satisfactory, in spite of the large outlay. A little later the question will force itself more prominently into notice, whether the four-line track or the separate fast through traffic lines, will best answer the purpose. The former possesses certain advantages, but the latter would give more freedom for high-speed running.