“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. Thus Mr. Hanna points out that as between a material that can be cleaned for 15 cents and one that can be cleaned for 30 cents, there is a difference of $3.15 per mile for cleaning, a difference of $15.75 per week, or $630 per season of 40 weeks—$6,300 in ten years. In Mr. Hanna’s judgment cleaning costs can be greatly reduced by a policy of prompt repair. He believes in the continual patrol of all city streets by men whose duty it is to discover defects in pavement and prescribe repair. Schedule of Street Cleaning The unit work must be established and the responsibility of each employee fixed in order to secure an economical administration of street cleaning. This principle is illustrated by the so-called “block system.” By this, each man is allotted to a definite area of pavement to clean, which varies in extent depending upon local conditions as to traffic, physical condition of pavement, location of street, proximity to public buildings, population, paving, alleys, street cars, right of way and frontage of streets.