A great deal of misinformed criticism exists in regard to train speeds. It is true that speeds up to 100 miles per hour are not physically impossible and have actually been obtained on experimental runs, but such very high speeds can only be achieved under exceptionally favourable conditions. Actually there are comparatively few trains in the world which average much over 60 m.p.h. There is an economic limit to the speed of a railway train because after a certain speed is reached, the cost of raising the speed by a few extra miles per hour increases out of proportion to the gain effected. In ordinary service conditions, average speed is reduced by station stops, curves, gradients, junctions, and local restrictions such as those over certain bridges or in mining areas. Moreover, punctuality is just as important as speed, and therefore a margin must be allowed for bad weather or other contingencies. During the last eighty years the weight of trains has greatly increased, and this has offset the greater tractive power of modern locomotives. Eighty years ago loads seldom exceeded 100 tons, but at the present time loads of 500 tons are hauled by a single locomotive. When all round average train speeds are raised, however, the available equipment can be utilized to better advantage owing to the increased mileage of rolling stock and the greater line capacity, and this must be set against the cost of increasing train speeds.