30 HIGHWAY CONSTRUCTION 



natural soil. The latter if kept in repair will for at least one-half 

 the year be preferred by teamsters. 



The minimum width of the paved portion, if intended to carry 

 two lines of travel, is fixed by the width required to allow two vehicles 

 to pass each other safely. This width is 16 feet. If intended for 

 a single line of travel, 8 feet is sufficient, but suitable turnouts must be 

 provided at frequent intervals. The most economical width for any 

 roadway is some multiple of eight. 



Wide roads are the best; they expose a larger surface to the 

 drying action of the sun and wind, and require less supervision than 

 narrow ones. Their first cost is greater than narrow ones, and that 

 nearly in the ratio of the increased width. 



The cost of maintaining a mile of road depends more upon the 

 extent of the traffic than upon the extent of its surface, and unless 

 extremes be taken, the same quantity of material will be necessary 

 for the repair of the road whether wide or narrow, which is subjected 

 to the same amount of traffic. The cost of spreading the materials 

 over the wide road will be somewhat greater, but the cost of the 

 materials will be the same. On narrow roads the traffic, being 

 confined to one track, will wear more severely than if spread over a 

 wider surface. 



The width of land appropriated for road purposes varies in the 

 United States from 49^ feet to 66 feet; in England and France from 

 26 to 66 feet. And the width or space macadamized is also subject 

 to variation; in the United States the average width is 16 feet; in 

 France it varies between 16 and 22 feet; in Belgium 8J feet seems 

 to be the regular width, while in Austria from 14 J to 26 J feet. 



Transverse Contour. The center of all roadways should 

 be higher than the sides. The object of this is to facilitate the flow 

 of the rain water to the gutters. Where a good surface is maintained 

 a very moderate amount of rise is sufficient for this purpose. Earth 

 roads require the most and asphalt the least. The rise should bear 

 a certain proportion to the width of the carriageway. The most 

 suitable proportions for the different paving materials is shown in 

 table 10. 



Form of Transverse Contour. All authorities agree that 

 the form should be convex, but they 'differ in the amount and form 



