Under the first category, Maintenance of Way and Structures, absorbing about one-fifth of operating expenses, over one-half is incurred for so-called "repairs of roadway." It is evident that a large part of this expense is due not to wear but to weather. A costly plant is exposed to every vicissitude of flood, fire, and waste. Re-ballasting and realignment may be somewhat more expensive where traffic is heavy; but certainly all general repairs, the wages of track walkers, the removal of snow, ice, and weeds, must be attended to entirely irrespective of the number or size of passing trains. Of the second item, renewals of rails, it is probable that this expenditure is directly traceable to wear and tear in large part. The more trains, the heavier the locomotive and cars or the higher the speed, the more rapidly must these rails be replaced. But even so, the proportionate amount is small, constituting generally between five and ten per cent. only of the group expenditure for maintenance of way. With ties, an item about twice as important as rails, the case is exactly the reverse. Ties rot out rather than wear out. They have a natural life varying from four to fourteen years, as influenced by climate, ballast, and drainage. The necessary expenditure per mile for them by different roads varies greatly, as might be expected; but it seems to bear little relation to the density of traffic. As for the principal remaining items under Maintenance of Way, such as repairs of bridges and buildings; if properly designed to withstand their loads and strains, most expenses of their up-keep such as repainting and reroofing should be practically independent of the volume of business. A recent elaborate discussion of these matters in 1907 in the Wisconsin Two-Cent Fare decision, reached the conclusion that all of the cost of rails, one-third of the ties and ten per cent. of expenditures for roadway, track and bridges, are all that can properly be charged to wear from traffic, as opposed to natural depreciation. Acworth illustrates this point by comparison of the Midland & Great Western Railway of Ireland and the Lancashire & Yorkshire Railroad. These two are of about equal length, approximately 530 miles. The latter carries forty times the traffic of the former road, and yet its expenses for maintenance of way are only eight times as much. It seems safe, in general, to conclude that in this first large group of expenditures for maintenance of the fixed plant, probably not over one-third are variable to any considerable degree. Acworth for England estimates this proportion at about two-fifths.