348 AGRICULTURAL, APPROPRLVTION BILL, 1924. 



the roads. Yet, this and other simUar studies are basic in hwin^ 

 the foundation far the whole consideration of the economics of high- 

 way transportation. 



Mr. Anderson. Has it 1)een shown tliat the overloading of tiucks 

 beyond their rated capacity has had a detrimental eflect npon the 

 roads, as well as upon the trucks? 



Mr. MacDoxald. Yes; in my judgment, that has been shown, 

 as applied to the heavier trucks; that is. the detrimental results 

 to the road are more pronounced if the heavier trucks are over- 

 loaded than if the lighter trucks are overloaded, but in any event, 

 there is a more detrimental effect from overloading a tinick of any 

 capacity, than from the same load carried upon a truck properly 

 designed to carry that load. This is due to the impact, of heavily- 

 loaded wheels upon the roads. It is po.ssible to multiply the static 

 load, that is, the load of the truck standing still by seven, if a large 

 obstiTiction on the road surface occurs, which drops the load on 

 the highway. The average equivalent impact of the moving 

 truck measured by the load of truck, stationary is about four times 

 the latter and it does not recpiire a very large obstacle to produce 

 a very considerable impact, varying with the speed of the truck. 



There is a long and involved task ahead of us to detrmine the re- 

 lation between the motor vehicle and the road, but during the past 

 year much progress has been made. 



Mr. Anderson. Well, it would seem from that statement that the 

 smoother the road and the better condition that it is kept in, the le.«« 

 will be the upkeep ? 



Mr. MacDonald. That is very true, sir. That is one of the reasons 

 why road maintenance becomes so absolutely important. An 

 accurately circular smooth wheel passing over a |)erfectly plane 

 road does not produce impact, but even a half-inch difference in the 

 surface of the road, with a solid rubber tire produces considerable 

 impact. On the Bates experimental road test in Illinois where the 

 weaker stretches of road were actually tested to destruction, after 

 the break started, it progressed along the road as much as 30 feet a 

 day. Up to a certain point, the road carried the load, but as soon as 

 the first break occurred, then the breaking down of the section 

 occurred at the rate of 30 feet a day. 



In addition to the traffic studies under this item, which we pro- 

 pose to carry on, we are making an analysis of highway linan<"e. 

 including the problems of the raising and expenditure of funds for 

 highway purposes in the States, to determine the j)rinciples uniler- 

 lying the proper distribution of the cost between (iu> s(>veral sources 

 of revenues. 



LAWS Ui;(H;i,ATlN(i TKAI'Kir. 



Mr. Buchanan. Let me get back to your (irst proposition for just 

 a minute. You are taking tiie census of the amount of trallic going 

 over the roads in certain States, the weights of the trucks, with an 

 idea, 1 suppose, of a law limiting the amount any truck can carry 

 or any vehicle ran ciiri'X' ^ 



Ml'. .MacDonai.I). 'I es, sir. 



Mr. !iu(;iiANA\. Have any of these States got such a law ^ 



Mr. MacDonai.I). !*iactic*allv all of the States have regulatory 

 laws. 



