In the popular mind curvature is perhaps the most objectionable feature of railroad alinement. The popular mind readily perceives the curvature as a fact, when a grade which is more costly from an operating standpoint is not perceived at all. The objections to curvature may be analyzed and classified as follows:

(1) Danger

The added danger of collision, derailment, or other form of accident which is due to curvature, are fully realized and even exaggerated by non-technical people.

(2) Effect On Traffic

A road sometimes loses passenger traffic on account of the apprehension. of danger, or because the curvature produces rough and unpleasant riding, or because it reduces somewhat the speed of trains and therefore the total time between termini.

(3) Effect On Operating Trains

Curvature has some limiting effect on the length of trains, and it is claimed that it limits the use of heavy engines.

(4) Effect On Operating Expenses

Curvature increases these expenses by increasing (a) the required tractive force; (b) the wear and tear of road-bed and track; (c) the wear and tear of equipment; and (d) the required number of track-walkers and watchmen. The above objections will be considered in order.

160. Financial Value Of The Danger Of Accident Due To Curvature

This subject has already been considered in Chapter I, under the general subject of accidents. Special objection is urged against curvature, on the ground that it increases the danger of accidents, that accidents are more liable to occur on a curve than on a straight track, and that when they do occur the results are apt to be far worse than when on a tangent. The subject is sometimes considered from the standpoint of eliminating curvature altogether, but this is usually financially if not physically impossible. We are chiefly concerned from a practical standpoint with an effort to obtain easy curvature rather than sharp curvature, or to reduce the number of degrees of central angle. If we study the statistics published each year regarding the total number of railroad accidents in the country and attempt to estimate the number which happened on curves, and then attempt to estimate the number of those accidents which would have been avoided if the track had not been curved, or if the track had had easy curvature rather than sharp curvature, it will be found that the estimated number for which curvature, and especially sharp curvature, was directly responsible is very small. If we can estimate the number of railroad curves in the United States, the immense train mileage on them, and then compute the probabilities that an accident will happen on any one particular curve during any year or during a term of say 100 years, we will find that the probabilities are exceedingly small. If we then attempt to compute, on the basis of these probabilities, how much money should be annually expended in order to avoid an accident which might probably happen in the course of the computed term of years, we would find that this annual sum would be absolutely insignificant. In fact we are forced to the conclusion that we are not justified in spending money to reduce curvature on account of the danger of accident. Of course this does not mean that there are not special cases in which accident is especially liable to happen and which thoroughly justifies a demand of expenditure to avoid it. For example, a very sharp curve in a mountainous region may circle around the end of a steep ridge, so that the view of the track is obstructed and prevent the engineer from discovering a landslide which might fall down from the steep side slopes. Such a case is an example of many cases of special danger which justify and demand the employment of special watchmen and flagmen to watch the condition of such dangerous places in the road. But these are simply exceptions which have no application to the general rule. We may therefore dismiss this phase of the question.