BITUMINOUS PAVEMENT BUILT ON MACADAM BASE 
Read before the American Society of Municipal Improvements by Linn 
lyhitc, Chief Engineer South Park Commissioners, Chicago, III. 
Macadam, for the purposes of this 
discussion, may be broadly defined as 
meaning all kinds of broken stone road 
surfaces bonded with more or less finely 
divided mineral matter, which may or 
may not be of the same material as that 
of which the body of the macadam is 
made up. Road surfaces made up of 
slag, chert or gravel which does not de- 
pend on a soluble clay as a binder, 
may be considered in this class. Where 
hydraulic cement or bitumen is used 
as a binder, the resulting composition 
is not macadam. 
It seems unnecessary to state that 
macadam thus defined is one of the old- 
est and most universally used forms of 
improved road surfaces, and that in 
many town and suburban districts it is 
almost the only road material used. In 
our cities, too, it constitutes a large 
percentage of the street pavements and 
is easily among the most valuable as- 
sets of almost any community. 
The city of Chicago, for instance, has 
600 miles of macadam, which is about 
50 per cent of all the usable street 
pavement in the city, and may be con- 
servativeh^ valued at $17,000 per mile, or 
a total of $10,000,000. All other 
street pavements in Chicago may be 
valued at $20,000,000. Thus 50 per cent 
of the area and fully 33 1-3 per cent 
of the value of all pavements in the city 
is macadam. These figures of value do 
not, of course, include the value of the 
land on which the pavements are built, 
nor do they include the value of any 
grading, curbing or drainage. 
Little Rock has 14.63 miles of mac- 
adam, costing $290,000 and 14.39 miles of 
all other kinds of street pavement, cost- 
ing $580,000, the percentage of area and 
value being about the same as in Chi- 
cago ; that is, about half the area of 
street pavements in the city is macadam, 
the value of which is about one-third of 
the total. 
I use these figures to emphasize the 
quantity of macadam in use and its 
money value. If macadam could be 
maintained at a reasonable cost in 
good surface without dust, it would be 
a very satisfactory pavement for many 
situations. Its tractive resistance is low 
when in good surface; it affords secure 
foothold for horses and motor cars; it 
is not so noisy as some other pave- 
ments, and its appearance is generally 
harmonious with the surroundings on a 
residence street, a park drive, or a su- 
burban highway. 
The cost of maintaining macadam will 
not be discussed at any length in this 
paper, as it is a large subject in itself, 
and would require the collection of* a 
TWO PORTABLE ASPHALT MIXING PLANTS IN OPERATION LAYING 2,000 SQUARE YARDS OP TWO-INCH 
PAVEMENT A DAY. 
