EE — eS 
ON THE ROAD PROBLEM. oe 
there is a broken ridge of dirt on both sides, and out beyond these 
-ridges are loose pieces of mud, thrown to some distance. I measured 
the discharge from a pothole, in a case where the mud had some con- 
sistency, and found that the pieces of mud thrown out reached more 
than six feet from the tire mark. The case was one in which the speed 
of the vehicle was not more than 15 miles an hour. I also show you a 
diagram of a pothole. It consists of a round group of stones, bare of all 
covering, and pushed down below the level of the road, and round it 
thick mud gradually thinning outwards. Every time a hoof or a wheel 
has to fall into it more dirt is thrown out. In wet weather it fills with 
water, which works its way all around, and brings the crust of the road 
to destruction. The increase of potholes is not caused by the change 
from horse to motor traffic. It is caused by increased traffic on roads 
hadly constructed. If anyone desires to be assured that potholes are 
formed by horse traffic, let him examine the Trossachs road, a road on 
which no motor vehicle is permitted to run. I went over a cross-road 
a few days ago, where not more than one motor-car passes in a month, 
and I found it full of potholes. There will always be potholes in roads 
where a good deal of traffic passes, as long as road metal is mixed with 
mud and rolled down, as is at present the practice. 
Another evil which developed itself as a consequence of the adoption 
of steam-rolling has been the too common use of stones of larger size 
than those prescribed by Macadam. His metal had to pass through a 
14-inch gauge. At first, for the guidance of the labourer, who was not 
to be trusted for careful measurement, he gave as a formula that the 
stone-breaker should be able to insert any of his stones into his mouth. 
But he had to give this up. When he was inspecting road work near 
Bristol, he came upon a pile of stones which were of much larger size 
than his specification to the contractor required. He at once found 
fault with the very tall stone-breaker, holding up to him a stone from 
the pile. The man, being a Scotsman like himself, responded in the 
vernacular: ‘ Weel, Mr. Macadam, ye tell’t iss to break doon till we 
cud pit the stone in our mooth. Look here ’—and he opened a vast 
jaw stretching from ear to ear, and, showing a cayern with no teeth, 
made the impugned stone disappear. This drove Macadam back to 
scientific rule, prescribing 13 inch and no stone to exceed six ounces in 
weight. He relied on the close packing of the small stone to give a 
good resisting surface, and did so successfully. But for a good many 
years his rule has been departed from. (Specimens of Macadam stone 
and of stone used now shown). Here is a stone which I picked out 
of a road, not a mile from this place. I put it in the scale, and I now 
count macadam stones into the other scale, and you see it takes 
21 macadam stones to balance the single stone, although it has lost 
some weight by being moved in the road, for as you see the edges are 
all completely rounded off. Let me illustrate to you the evils of using 
large stones. I have laid in this box some ordinary macadam. On 
the top are three stones, one of macadam size and two of greater size, 
which were taken from a road. I have attached sticks with coloured 
discs to the stones. When I press on the macadam stone the disc 
does not rise, as the stone does not tilt, but when I press on the others 
