HIGHWAY CONSTRUCTION 129 



ments, involves the consideration of a wide array of diverse circum- 

 stances. Rough-surfaced pavements, when in their best condition, 

 afford a lodgment for organic matter composed largely of the urine 

 and excrement of the animals employed upon the roadway. In 

 warm and damp weather, these matters undergo putrefactive fer- 

 mentation, and become the most efficient agency for generating and 

 disseminating noxious vapors and disease germs, now recognized as 

 the cause of a large part of the ills afflicting mankind. Pavements 

 formed of porous materials are objectionable on the same, if not even 

 stronger, grounds. 



Pavements productive of dust and mud are objectionable, and 

 especially so on streets devoted to retail trade. If this particular 

 disadvantage be appraised at so small a sum per lineal foot of frontage 

 as $1.50 per month, or six cents per day, it exceeds the cost of the best 

 quality of pavement free from these disadvantages. 



Rough-surfaced pavements are noisy under traffic and insufferable 

 to nervous invalids, and much nervous sickness is attributable to them. 

 To all persons interested in nervous invalids, this damage from noisy 

 pavements is rated as being far greater than would be the cost of sub- 

 stituting the best quality of noiseless pavement; but there are, under 

 many circumstances, specific financial losses, measurable in dollars 

 and cents, dependent upon the use of rough, noisy pavements. They 

 reduce the rental value of buildings and offices situated upon streets 

 so paved offices devoted to pursuits wherein exhausting brain work 

 is required. In such locations, quietness is almost indispensable, 

 and no question about the cbst of a noiseless pavement weighs against 

 its possession. When an investigator has done the best he can to 

 determine such a summary of costs of a pavement, he may divide the 

 amount of annual tonnage of the street traffic by the amount of annual 

 costs, and know what number of tons of traffic are borne for each cent 

 of the average annual cost, which is the crucial test for any comparison, 

 as follows: 



(1) Annual interest upon first cost $ 



(2) Average annual expense for maintenance and renewal . . . 



(3) Annual cost for custody (sprinkling and cleaning) 



(4) Annual cost for service and use 



(5) Annual cost for consequential damages 



Amount of average annual cost 



Annual tonnage of traffic 



Tons of traffic for each cent of cost 



Gross Cost of Pavements, Since the cost of a pavement depends 



