SOME SPECIAL PROBLEMS OF VALUATION 73

expenses of a railroad are not specially incurred in connection
 with the rendering of any specific service or class of
services, but for the maintenance of the general equipment.
Incidentally they afford facilities for special classes of traffic,
and all kinds of traffic would suffer from inadequate provision
for these general expenses. It is only in respect of the
special outlay associated with a particular shipment, or class
of shipments, that we can arrive at the direct cost of the
service rendered. For convenience of treatment the following
rough division of expenses may be made :—
(x) Cost of loading and unloading and cost of labour
and materials used in forwarding any particular consignment.
If the consignment form only a fraction of a train-load, a
large part of these costs is shared with other consignments.
To avoid confusion, let us assume that a train-load is dealt
with,
(8) Maintenance of road-bed and rolling - stock and
general expenses of railroad staff, (i) If special rollingstock
 is required for the traffic in question, its cost of
maintenance may be treated as special to that class of
traffic, though not to the particular consignment. (ii.) If no
special cars, etc,, are reserved for that class of traffic, the cost
of maintenance of cars, etc, is shared with other classes of
traffic.
(y) Payment of interest on bonds and dividend on stocks.
Were the expenses under the heads (3) and (y) to be
divided pro rat2 among all the traffic, at an appropriate tonmile
 or other uniform rate, a fiction of regulating rates by
cost of service would be maintained. But it would be
only a fiction, since such a pro raz division lacks rational
justification. The general principle followed in practical
settlement of rates is known as that of charging “ what the
traffic will bear” It may be expressed somewhat as follows.
The rate charged must cover at least the expenses (a).
These expenses are loaded, for each class of traffic, on the
principle of making that traffic yield as large a contribution
as possible towards (3) and (y). In accordance with principles
 examined earlier in this chapter, it appears that an
attempt to overburden any special class of traffic might