A study made by the Chicago Civil Service Commission definitely established that the density of horse traffic, which is the total number of horses passing through a given street divided by the width of the street, is the principal factor which determines the number and frequency of cleanings one street should be given.
The Commission has also learned that there are at least thirty-eight distinct movements which a street cleaner makes in street cleaning work. Of these some have been found to be unproductive, resulting in loss of time and energy and less effective street cleaning. The most important of these, according to the Commission’s report, are as follows: Observation of time wheeling push carts into alleys or other dumping places, disclosing that practically one-fifth of time was consumed in this activity. The study disclosed that some sweepers are more efficient than others, due to the stroke of the broom which they make. The practise of hitting a broom on the pavement is not necessary on dry pavements and very seldom on wet pavements. Effective and practical street cleaning can be obtained by bringing the brush down forcibly at the beginning of each stroke, thus reducing the work at least 15 per cent. The time schedules disclosed that time lost by street cleaners in dodging horses and automobiles where traffic is dense is unappreciable and does not exceed 8 per cent. of the total time in the business district and not more than 2 per cent. of the total time in the outlying district. It is occasioned more through congestion of traffic than through density of traffic. In cleaning light traffic asphalt pavements it was disclosed that after the one morning thorough cleaning three-fourths of the area to be covered during the remainder of the day does not require thorough cleaning. The Commission believes that scoops equipped with rollers would be well adapted for use on light traffic pavements, and with them one man could patrol a much larger pavement area and still keep the pavement in good condition. Time studies of work performed by street laborers working in gangs showed that work done by groups and gangs was not as economical as the division of such work through individual arrangements. Considerable time is lost in conversation. When one man rests every man on the street does the same thing. While working in gangs the good sweeper does no more work than the poorest of the gang. Where it is desired to cover a large area of street with men working in groups rather than in gangs it would be better, the Commission thinks, for each man to have a definite uniform area to cover and to require the foreman to time each individual.
Mr. Edward D. Very, Sanitary Engineer, says that any attempt to estimate the amount of materials which accumulate on a city street must end in failure as the contributing elements vary in different localities in a city and in different cities, and where figures are given they do not really present any valuable data. Some general principles, however, have been determined. The Chicago Commission in its investigation declares that the quantity and volume of dirt attributed to horse drawn vehicle traffic is the most important source of street dirt. The loss of sand and coal and crushed stone, hay, manure and other loose material from poorly constructed vehicles or overloaded vehicles adds greatly to the quantity of street dirt to be removed. Important in a wet season is the dirt carried by moving vehicles through streets and alleys onto hard pavements, but the Commission says that the amount of dirt actually attributable to this source is considerably less than is usually believed. There is also considerable refuse in the form of leaves and grass which accumulates in the residential streets and along boulevards and parks, which has a tendency to lodge in catch basin inlets and stop the free flow of storm water. The quantity of leaves accumulating in the short leaf season on streets far exceeds that which naturally drops onto the surface of streets alone, because of the additional cleaning from lawns and parkway spaces.
Some reports express the belief that when a fixed standard is established of basing street cleaning schedules carefully on density of traffic, condition of pavement, character of frontage and kind of pavement, a definite relation will be found between the amount of street sweepings collected and the number of sweepers employed. In Chicago it has been found that different sweepers average daily collections of quantities varying from three-fourths of a cubic yard to three cubic yards. It has also been noted that street sweepings collected by regular block sweepers average about .0045 cubic feet per square yard. The weight of sweepings will, under ordinary conditions, approximate 36 pounds per cubic foot.
The paving and repair policy of a city is a very important factor in cleaning rates. Comparatively few cities as yet give any thought when selecting a particular pavement as to the relative cost of keeping it clean. It is also a fact that in many cities repair work is neglected at the expense of cleaning.
A smooth, hard surface pavement will cost less to keep clean than one with a rough or uneven surface. A brick pavement, for instance, costs more to keep clean than sheet asphalt. For the same reason a street out of repair is more expensive to clean than one in good repair.
Officials agree that a paving policy should be carried out with a view to having a minimum number of unpaved approaches to existing pavements in order to prevent mud being tracked from the highway to pavement. There is need also of protecting narrow rural pavements from the overflow or tracking of mud that originates on adjacent portions of the same highway.
In a discussion of paving policies and their relation to street cleaning Mr. Hanna says: “The construction and maintenance of pavements that are easy to clean are important and effectual in saving the cost of street administration. Little weight is given to cleaning cost when paving questions are settled and an actual expense of $500 a mile in repairing residence streets would be considered an appreciable item of maintenance, yet that figure for cleaning a mile of residence streets through a season is extremely low. A street cleaner looks upon two qualities in a pavement. It must be smooth and particles of litter must not stick to the surface. The question of smoothness opens up the whole matter of durability. Any material that deteriorates or roughens becomes more difficult each year to clean. Any neglect of needed repairs means a larger cleaning bill until the repairs have been completed. The twofold expense resulting from wear, the cost of repairs plus the increased cost of cleaning should enter into all calculation of expense. Additional calculation of cleaning expense must be made for all bituminous pavements on account of the sticking of particles of litter to the surface. These surfaces are never quite so clean as non-adhesive materials and it costs from 25 per cent. upwards in additional cost to put them in a reasonably presentable condition on account of this quality. This difficulty is seen at its worst in a new creosoted wood block pavement, when the oil is gradually working out between the pores of the wood. The use of steel scrapers must often be employed as the flushing by water is not at all effective in removing the dirt from the surface.
“Substances most easily cleaned that enter into pavements are brick and stone. Neither originates any dirt, and both wash off readily. The only ground for discrimination between them is on the question of smoothness where brick has a slight advantage as a rule. In the use of these materials the choice of a filler is all important. A bituminous filler has all the disadvantages of a bituminous surface. Being softer than the brick or block it recedes, leaving a crevice that invites lodgment of dirt; with edges of brick or block unprotected it is sure to roughen, thus adding to the difficulties of cleaning. Such a street after a few years presents the appearance of cobble stones with the filler invisible or else melted and run to the gutter where it impedes work of follow-up gang.”
Mr. Hanna recommends only a cement grout filler. He says that West 14th Street in Cleveland has a grouted brick pavement ten years old and a traffic of two vehicles a minute. It is cleaned on an average of five times a week, being flushed by night and hand swept by day. The cost of cleaning is almost exactly 15 cents per 10,000 of square feet. This is the lowest figure the city has been able to reach on any type of pavement. Mr. Hanna says that the cost on the best asphalt would not be less than 20 cents and would rise to 30 cents if the surface became wavy or rough. Wood block costs approximately $1.00 a square to clean in its initial condition, and it would be at least two years before oil will have dried out sufficiently to admit its being cleaned for 30 cents a square. Tar filled brick pavement will cost not less than 30 cents a square, and if the filler disappears and the block roughens this cost will amount to 60 cents or more. In the case of a pavement 40 feet wide there are about 21 squares to a mile.