Of the 208,361 square yards, 88%

is an asphaltic concrete 2 inches thick, and 12% is a sheet asphalt 11⁄2 inches thick, on a 2-inch binder. The base under one section of the sheet asphalt type was an old brick pavement, and under the other section an old stone block pavement. The base under the asphaltic concrete is either concrete or macadam.

5

131,000

366230

79835

6:007

53166

26,719

a260

The thickness of the concrete base varies. Twenty-three per cent of the yardage is on 7 inches of concrete, 3% on 6 inches, and 37% on a base that is 6 inches thick at the sides and 7 inches in the center. The concrete base is a 1-212-5 mix. Reinforcing steel was used in 23% of the yardage.

The macadam base is 10 inches thick, built in two 5-inch courses. Twenty-five per cent of the yardage is on this type of base.

Figure VII is a graph showing the repair cost per square yard per year for all asphalt pavements.

Remarks on Asphalt Types

Ninety per cent of the total repair cost was spent on one road which was a complete failure. The repair cost of this pavement was more than three times its first cost. The base under this pavement was 6 inches thick at the sides and 7 inches in the center. The sub-grade was a clay soil with low supporting value. The traffic on this road was heavy, a large part being truck traffic.

This county's experience with asphalt pavements has been so limited and the results so erratic that the cost data is of little value.

The average original cost per square yard for the asphalt pavements was $2.84.

Traffic

The graph (Fig. VIII) showing the motor vehicle registration in the county, when considered in the light of the fact that the county's population has tripled in the last twenty-five years, will give some idea of the service rendered by these pavements in the development of this rapidly growing community.

A recent traffic survey on the principal highways in Cuyahoga County, revealed a traffic on some of them amounting to 3,500 tons per day between the hours of 6 a. m. and 6 p. m. Figuring only three hundred days in the year, this would totak an annual tonnage of 1,050,000. It is reasonable to estimate that these pavements of early design and construction, built for light and slowly moving vehicles, have been carrying on an average of one million tons of modern traffic per year for at least the last five years.

The brick pavements being the type first laid in the county, naturally were laid on the principal traffic arteries and closest in to the city. Several of our heavy traffic routes are also paved with asphaltic types.

Conclusions

bulk of maintenance costs, were unstable subgrades, inadequately In the rigid types of pavements, the two things responsible for the drained, and weak, inferior bases. This fact is established by the excellent conditions of those sections of these old pavements that are found on sandy or gravelly soil.

In the non-rigid types, the principal causes for much of the repair necessary are under-design, cutting of the thickness to obtain a low first cost, and poor judgment in placing unsuitable types of pavement on roads where traffic and soil conditions demanded a better type. It is evident that it would have been more economical to have rebuilt or reconstructed those pavements that required excessive repair, rather than to have kept them in service by patching them from time to time.

One of the surprising things brought out from this study of repair costs is the excessive repairs made to pavements of some types built since 1915. Several have had considerably more than their first cost spent in repairs, and this, too, before they had rendered ten years of service. In short, property owners needed a new pavement before the ten-year bonds on the old one had been retired.

Mr. Simpson from his studies of repair costs on city pavements in Columbus, Ohio, found a critical period in the life of heavy traffic pavements. This period was from nine to thirteen years. Cuyahoga County's experience seems to prove this critical period to be at about the same time.

However, we must realize, both in the case of Columbus and Cuyahoga County, that we are considering a large yardage of pavements that were designed and constructed either before the advent of heavy traffic as we know it today, or during the early phases of this heavy traffic. Whether this same critical period is to be found nine to thirteen years hence in pavements designed and constructed today is another question.

In conclusion I think it behooves engineers who are designing pavements to put more of the "repair cost" in "first cost" instead of letting some road commissioner put it in later in "after cost."

DISCUSSION

MR. NYE: Mr. Thomas spoke of not finding the stone which should have been there. We had a similar experience in New Bedford, Massachusetts. We knew the stone should be there, because we placed it there by city forces. We used granite and later found nothing left. It had simply been ground up and disintegrated entirely, due to excessive brittleness.

In regard to the talk this morning about taking advantage of the granite bases; we took advantage of the granite base just before the war on one of our heaviest-traveled streets. We put on this a twoinch bitulithic surface. It was laid across a marsh and was subjected to the heaviest sort of traffic, yet it is as good today as when we laid it in 1917.

PRESIDENT HATTON: That stone was granite?

MR. NYE: Yes, sir.

PRESIDENT HATTON: And it had disintegrated?

MR. NYE: Yes; there was probably ten inches of stone originally on that street.

PRESIDENT HATTON: You must have an unusual granite in that part of the country.

(Thereupon Mr. Thomas showed some pictures.)

PRESIDENT HATTON: Mr. Thomas is certainly one of the most thorough statisticians I have ever heard before this Society in many days. Seldom have such complete unit and repair costs been presented to the Society; and it is quite a valuable contribution. The Chair will gladly entertain any reasonable discussion of this valuable paper.

MR. SCHWEMLER: Does your study reveal the average life of the hard type of pavements?

MR. THOMAS: Not positively. I think it gives some light upon it, though. It proves that there is no such thing as permanent pave

ments.

PRESIDENT HATTON: I think Mr. Hirst brought out the lack of permanent pavements very well this morning. We once called bitulithic top pavements permanent and now we call concrete pavement permanent, whereas going outside of my own good city of Milwaukee a very excellent concrete pavement is being repaired by the State throughout two or three miles. I agree with Mr. Hirst that engineers must not allow the word permanent to be used in connection with pavement, because it deceives the layman that puts up the taxes with the expectation that those roads are going to last as long as he lives.

SNOW REMOVAL IN DETROIT

By G. R. Thompson, Superintendent, Division of Municipal Waste, Detroit, Mich.

came.

Within the memory of most of us we accepted the seasons as they If dirt roads were impassible in the Spring, no one tried to use them; Summer was expected to be hot and dusty; Fall brought leaves; and Winter brought snow. These natural consequences of the weather were considered inevitable and we individually prepared for, and met them. But as we congregate more congestedly in big cities we become less independent as individuals and more dependent as units of a large social body. The dirt road is now a concrete superhighway open 365 days in the year; our buildings are cooled and the city street is washed and swept free of dust in Summer; the leaves must not stop the catch basins in Fall. Seventy degree building temperatures with light clothing, to suit, have replaced the red flannels and boots; the heated closed car that starts at 20 degrees below zero is standard household equipment; concrete pours protected throughout the year and in general the human race is ever striving to carry on comfortably regardless of the weather. We don't want to let Winter interfere and that is the reason for snow cleaning. "That people's wants have been unseemingly set out before their needs is intentional because they are the immediate actuating motive in service-the quick tricks-whereas the needs or necessities are often unpopular expenses whose fulfillment is largely taken for granted. The want for snow removal is principally a requirement of pedestrian traffic, but the necessity for removal or other handling is a requirement of vehicular traffic. The combination of both the pedestrian and vehicular point of view is the sound economic reason. for getting a full year 'round return out of the vast investment that the citizens carry in pavement."

Snow removal for pedestrian traffic is a warranted expense in preserving public health and safety. Poetry to the contrary notwithstanding, city snow is not pure, clean and white. After snow serves as a precipitating medium, passing through impure city atmosphere, it becomes a holding medium on the streets and in the gutters for all natural street dirt, and if allowed to freeze in, as it will, the gutters become filled with refrigerated, but potential germ carrying filth, that is so noticeable on neglected streets in the first Spring thaws. Wet feet in the office, store or factory, and homeward-bound for a long ride, are not conducive to good health. Slipping accidents, resulting in suffering and lost time multiply with ice and snow. Pedestrians suffer collectively as well as individually from snow, in inter