_Answer._ 1. Locomotives for “switching,” “shunting” or “drilling” service, that is, for transferring cars from one place to another at stations; 2, for freight traffic; 3, for ordinary passenger traffic, and 4, for suburban or metropolitan railroads, where a great many light trains are run. QUESTION 428. _What kinds of locomotives are used in this country for switching cars at stations?_ [Illustration: Fig. 220.] _Answer._ Four-wheeled locomotives similar to that shown in Plate IV. In some cases they are made with six driving-wheels. Engines like that shown in Plate IV have separate tenders, but they are sometimes made so as to carry the water-tank and fuel on the locomotive itself, as shown in fig. 220, and are then called tank locomotives. Fig. 220 represents a switching engine built by the Taunton Locomotive Manufacturing Company. QUESTION 429. _Why are four-wheeled locomotives used for switching?_ _Answer._ Because in such service it is constantly necessary to start trains, many of which are very heavy, and therefore a great deal of adhesion is needed. For this reason the whole weight of the locomotive and in the case of tank locomotives that of the water and fuel is placed on the driving-wheels. It is also necessary for such locomotives to run over curves of very short radius and into switches whose angle with the main track is very great, and therefore in order that they may do this and remain on the track, their wheel-bases must be very short, and consequently the wheels are all placed near together between the smoke-box and fire-box. QUESTION 430. _Why are such locomotives not suited for general traffic?_ _Answer._ Owing to the shortness of their wheel-bases they become very unsteady at high speeds, and acquire a pitching motion, similar to that of a horse-car when running rapidly over a rough track. This unsteadiness not only becomes very uncomfortable to the men who run the locomotive, but there is danger of the engine running off the track. As nearly all switching is done at very slow speeds, it is not so objectionable for that service as it would be on the “open road”[102] at high speeds. [102] The term “_open road_” is a literal translation from the German, for which there is no corresponding English term, and means the road between stations where trains run fast. QUESTION 431. _What kinds of locomotives are used for freight service?_