The organization of the Master Car Builders, in 1867, solved that problem. This organization, through committee, made first the freight car standard and then the passenger standard. Axles, bolts, king-pins--every one of the intricate car-parts--were brought to standard and numbered sizes. After that all that a master mechanic had to do was to keep an assortment of standard car parts in his store-room, and he could make reasonable repairs to any car that travelled rails. The standardization has gone steadily forward year by year; it has included a variety of things, even such details as systematic numbering and lettering of cars. It is one of the evidences of the constant bettering of the American railroad, the steady effort to bring it to an economical and scientific basis. Recently some of the railroads have made intelligent experiments, seeking to devise a vehicle that should be both locomotive and car, and that should be especially adapted for small side-lines, where traffic runs exceedingly light. Some success has been found in the use of a passenger coach, into which a gasolene engine has been introduced, and several of these cars are in regular use in the West. Two or three of them have been employed for three or four years on Union Pacific branches in and around Denver. They render a possible solution for one railroad problem--the problem of providing sufficient service for some branch where local traffic is slight. The gasolene car requires but two men, as against a minimum crew of five men for even the smallest steam passenger train. It can be quickly handled, will make many successive stops readily, and generally provides an efficient addition to the regular passenger equipment. A few years ago it would have given the standard steam railroads an excellent weapon against the constant encroachments of paralleling electric roads through their good passenger traffic districts; even to-day it offers a possible solution of the difficult problem of the very small branch side-lines. CHAPTER IX REBUILDING A RAILROAD RECONSTRUCTION NECESSARY IN MANY CASES--OLD GRADES TOO HEAVY--CURVES STRAIGHTENED--TUNNELS AVOIDED--THESE IMPROVEMENTS REQUIRED ESPECIALLY BY FREIGHT LINES.