Asphalted roadway 1·0 Paved roadway, dry and in good order 1·5 to 2·0 „ „ in fair order 2·0 „ 2·5 „ „ but covered with mud 2·0 „ 2·7 Macadamised roadway, dry and in good order 2·5 „ 3·0 „ „ in a wet state 3·3 „ „ in fair order 4·5 „ „ but covered with mud 5·5 „ „ with the stones loose 5·0 „ 8·2 There are four forces constantly at work tending to destroy the momentum of vehicles passing along a roadway: they are gravity, collision, friction, and the resistance of the air. The first of these is lessened by easy gradients in a road, the second can be overcome to a great extent by evenness of surface, the third by hardness, and the fourth, as well as all the others, by giving sufficient foothold to the animal drawing the vehicle. Another excellent table[9] prepared from experiments made by Mr. Amos on different descriptions of pavement in the City of London may be useful, and is here given:-- -------------------+---------+-------+--------+-------------- | Speed | | |Tractive Force Road Material. |in Miles |Draught|Fraction| in Decimals |per hour.|in lbs.|of Load.| of the Load. -------------------+---------+-------+--------+-------------- Gravelly Macadam in| 6·945 |126·6 | 1/45·3 | ·0219 a side street | 3·45 |114·322| 1/50·3 | ·0197 | | | | | 5·15 | 70·963| 1/81·1 | ·0123 Granite pitching by| 3·196 | 41·932| 1/137·3| ·0072 side of tramway | 2·557 | 47·572| 1/121 | ·0082 | | | | Granite Macadam | 4·239 |262·886| 1/21·9 | ·0456 “freshly laid” | 2·775 |242·726| 1/23·7 | ·0421 | | | | | 5·025 | 91·525| 1/64·9 | ·0158 Asphalte Pavement | 3·56 | 69·753| 1/82·5 | ·0121 | 5·687 | 84·268| 1/68·3 | ·0111 | | | | | 3·932 |118·163| 1/48·7 | ·0205 Wood Pavement | 3·278 |102·412| 1/56·2 | ·0177 | 3·827 |100·066| 1/57·5 | ·0173 | | | | Macadam road, very | | | | good on Victoria | 6·65 |109·06 | 1/52·7 | ·0181 Embankment | | | | -------------------+---------+-------+--------+-------------- The following table from Law’s ‘Rudimentary Treatise on Civil Engineering’ shows the force required to move a load of a ton weight on different descriptions of roadway, the limiting angle of resistance, and the greatest inclination which should be given to the road being also stated.