Layout, facilities and activities relating to making road-tests of motor vehicles at the 1125-acre proving grounds of the General Motors Corporation near Detroit, this tract being designed to provide a place where road conditions are suitable for obtaining data that can be interpreted accurately, compared with similar data and used constructively, are outlined and illustrated. Adequate facilities are provided and ideal road-conditions have been established so that motor-vehicle tests involving endurance, speed, acceleration, hill climbing, riding-quality and other comparative tests can be made. Conditions are such that tests can be repeated from day to day, thus compensating for the variations of the weather and other factors. Complete and conclusive tests can be carried out readily and promptly, and the results are free from guesses and personal opinions.
The speed track is 20 ft. wide and nearly 4 miles long. Traffic is in one direction, clockwise. The turns are banked and can be driven over safely at a speed of 65 m.p.h., the high-speed cars passing the slower traffic by using the well-banked part of the roadbed.
The 1⅜-mile concrete straightaway course runs east and west and is equipped with graveled loops at each end so that runs can be continued in either direction without gearshifting or stopping; all tests are run in both directions and then averaged to cancel out the effects of wind. It is over this course that acceleration; deceleration; rolling-friction; riding-quality; fuel-economy at fixed speed, minimum-speed and maximum-speed; and similar tests are carried out. Another interesting facility is the concrete under-water roadway, which is 200 ft. long with 100 ft. of level section 12 ft. wide equipped with parapets to permit flooding to a depth as great as 2 ft. Special tests can be made here by driving vehicles through varied depths of water.
Three test hills having continuous accurate gradients furnish means for measuring, comparatively, engine powers under driving conditions. An endurance-test route winds through one portion and connects the test hills with the speed loop; gradients as high as 24 per cent are included.
The proving-grounds activities include the carrying on of endurance tests and experimental-car operation by each division of the Corporation and the comparative engineering and endurance tests of such cars in current production as may be of interest. The various tests made are enumerated, and many details of the methods of test procedure are stated, together with descriptions of the testing equipment.


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