1-2-5 | Earth road |Dust 3/4 to 2 in.| 298.0 | 99.3 3-3 | Earth |Mud, stiff, firm | 654.0 | 218.0 | | underneath | | 6-7 | Gravel |Loose, not packed| 789.0 | 263.0 ----------+-----------------+-----------------+-----------+----------- [1] Prof. J. B. Davidson in _Engineering News-Record_, August 17, 1918. [2] Graphic record indicates that the load was being accelerated when test was started. [3] Drawn with motor truck at 2-1/2 miles per hour. [4] Drawn with motor truck at 5 miles per hour. Comparatively few data are available showing the tractive resistance of motor vehicles, but the following tables are based on sufficient data to serve to illustrate the general trend. These data on the tractive resistances of an electric truck with solid rubber tires on asphalt and bitulithic, wood, brick and granite block, water-bonded and tar macadam, cinder and gravel road surfaces were obtained by A. E. Kennelly and O. R. Schurig in the research division of the electrical engineering department of the Massachusetts Institute of Technology, and are published in Bulletin No. 10 of the division. An electric truck was run over measured sections, ranging from 400 to 2600 feet in length, surfaced with these various materials, at certain speeds per hour, ranging from about 8 to about 15.5 miles per hour. The result of the observations of speeds, tractive resistances, conditions of surfaces, etc., were collected and studied in various combinations. TABLE 6