These trains never stop, except when signalled so to do. The interlocking apparatus, however, makes it impossible that one track should be open except when the other is closed. An accident, therefore, can happen only through the wilful carelessness of the engineer in charge of a train;--and in the face of wilful carelessness laws are of no more avail than signals. If a man in control of a locomotive wishes to bring on a collision he can always do it. Unless he wishes to, however, the interlocking apparatus not only can prevent him from so doing, but as a matter of fact always does. The same rule which holds good at junctions would hold good at level crossings. There is no essential difference between the two. By means of the interlocking apparatus the crossing can be so blocked at any desired distance from it in such a way that when one track is open the other must be closed;--unless, indeed, the apparatus is out of order, and then both would be closed. The precaution in this case, also, is absolute. Unlike the rule as to stopping, it does not depend on the caution or judgment of individuals;--there are the signals and the obstructions, and if they are not displayed on one road they are on the other. So superior is this apparatus in every respect--as regards safety as well as convenience--to the precaution of coming to a stop, that, as an inducement to introduce an almost perfect scientific appliance, it would be very desirable that states like Massachusetts and Connecticut compelling the stop, should except from the operation of the law all draw-bridges or grade-crossings at which suitable interlocking apparatus is provided. Surely it is not unreasonable that in this case science should have a chance to assert itself. [21] "As affecting the safe working of railways, the level crossing of one railway by another is a matter of very serious import. Even when signalled on the most approved principles, they are a source of danger, and, if possible, should always be avoided. At junctions of branch or other railways the practice has been adopted by some companies in special cases, to carry the off line under or over the main line by a bridge. This course should generally be adopted in the case of railways on which the traffic is large, and more expressly where express and fast trains are run." _Report on Accidents on Railways of the United Kingdom during 1877, p. 35._