be closed, do I understand that you would not have the authority to say this bridge must be closed? That is a power of the State or municipality, that correct?

Mr. TURNER. I think we would have no real problem on that, Senator, because if such a set of circumstances existed I am sure that in pointing it out to the State that we would not need immediate action with or without the threat of cutoff of future Federal aid. The State would be just as interested as we in the State operation of that structure and I am quite sure that the situation of that kind brought to their attention would result in immediate corrective action. Senator COOPER. I assume it would, too, but there is always a human element that enters into these cases.

I must say that failure of the Point Pleasant Bridge has caused a great many State highway commissions to go to work immediately to inspect their bridges. I know that in my own State of Kentucky, I think the first act of the new Governor in December was to order the State highway commission and its engineers to inspect all the bridges in Kentucky on Federal-aid systems, starting with those bridges over the Ohio River into Kentucky. That is a good thing. But it may indicate also that not only in my State, but in others, there has not been as much attention to this subject as there is now, because of that tragedy.

The CHAIRMAN. Of course, Senator Cooper, that catastrophe did cause the immediate concern in the matter, so too in any type catastrophe, whether it is a fire in a building resulting in an inspection of that building. If we have an airline tragedy, why, there is an effort very quickly to try to tighten the procedures with reference to the facilities that are used both on the ground and in the planes, themselves. It is very natural and I think very proper that we take a quick, prompt look and then follow it with the thoroughness with which I hope this hearing will develop.

That is the spirit, Mr. Bridwell, as I announced in my opening statement, the concept of what we are doing here today and in the succeeding hearings.

Mr. BRIDWELL. We appreciate that, Senator. It is our purpose to tackle the assignment of committee 3 with developing substantially improved procedures, inspection criteria which will be beneficial long into the future.

Returning to my prepared statement, I had mentioned that many bridges are beyond the responsibility of the Bureau of Public Roads and the State highway departments. Accordingly, representatives of the American Association of State Highway Officials and the Association of American Railroads were requested to meet with representatives of the Department of Transportation and the Corps of Engineers to discuss this problem. The meeting was held in Washington January 19. In this meeting, the railroad association representatives indicated that all rail lines had developed their requirements for bridge inspection, rating, and maintenance practices. Their bridges are inspected and rated at frequent intervals, and the industry has for many years published comprehensive instructions for inspection and load rating of bridges carrying railroad traffic.

It was determined the highway and railroad groups should work separately in the analysis of the standards and procedures required, since each group already had much accomplished and no purpose was served by acting jointly.

The Association of American Railroads circulated questionnaires to nearly 500 railroads, representing 99 percent of the railroad mileage in the country. A preliminary report on the results of this survey was was sent to me on March 5 by Mr. T. B. Hutcheson, assistant vice president of the Seaboard Coast Line Railroad and chairman of the Railroad Bridge Safety Committee of the Association of American Railroads.

A copy of this preliminary report is submitted for the record here today, together with excerpts from the American Railway Engineering Association "Manual of Recommended Practice for Railway Engineering" which pertain to the inspection and load rating of railroad bridges.

Representatives of AASHO and the Bureau of Public Roads developed "An Informational Guide for Inspection of Highway Bridges,' which will provide guidelines to States, cities, counties, and others responsible for highway bridge maintenance and inspection on an inspection program which will achieve the objective of the committee's assignment—that is, assure the safety of the Nation's highway bridges.

Many of the guides are a part of existing inspection manuals, but the gathering of these criteria into a single document with added instructions as to the inventory and rating of bridges as well as the timing and depth of inspection to be undertaken will be a valuable tool in the hands of those doing the work.

This guide manual was issued by the Bureau of Public Roads with its instructional memorandum, IM 40-1-68, "Bridge Safety Inspection," dated March 12, 1968. A copy of the guide and the instructional memorandum are attached to my testimony.

The Office of Research and Development of the Bureau of Public Roads on March 1, 1968, issued a circular memorandum on its program for developing the "Loading History of Highway Bridges," which will gather data needed for the development of techniques for more precise structural design and incorporation of new materials and structural concepts. A copy of this memorandum is also attached.

A separate instructional memorandum covering an inventory of all highway bridges is being prepared in the Bureau of Public Roads and will be issued soon. The inventory will fill an existing gap in our knowledge of the age and rating of highway bridges in the country.

These comments cover in general terms the present status of this committee's work. I know there are many more detailed items of information which you desire to have covered, and I will be pleased to answer questions regarding these matters. We also will be pleased to furnish additional information, as requested, on questions which we may not be able to answer today.

The CHAIRMAN. Thank you, Mr. Bridwell.

The memorandum and the correspondence, the material which accompanies your excellent statement, is going to be very helpful to our subcommittee and to the committee. I am sure the members of the subcommittee will want to have the material available for study. I thank you very, very much.

Senator Cooper, do you have any questions or comment?

Senator COOPER. Yes, Mr. Chairman, a few. I, too, thank you, Mr. Bridwell and Mr. Turner, for your very fine statement and for the work that has been done and is being done in this field.

I would like to relate this question to another bill that is before this committee, Senate bill 2658, to raise the weight limits on trucks. Do you know how many bridges are on the existing Interstate System?

Mr. TURNER. Well, when finished, Senator Cooper, there will be about 10,000 major bridges. Minor structures, including overcrossings and things of that nature, probably another 30,000.

In many cases, in most cases in fact, those will be double structures and there is a structure on each of the two opposite direction roadways so that you can probably double the number that I gave you to get the number of actual structures that had to be designed and maintained.

Senator COOPER. Have the bridges that have thus far been constructed on the Interstate System been constructed to meet stresses and loads beyond the present levels of permissible weights of trucks?

Mr. TURNER. Yes. Of course, they were carrying heavier loads, Senator Cooper. The design loading is generally based on what we designate as an H-20 S-16 type of loading meaning a 20,000-pound axle loading or a 20-ton truck with 80 percent of the loading on the rear axles and 20 percent on the front axle and a trailer with axles also at 16 tons.

The loadings that you have been discussing in the committee here in connection with S. 2658, I think it is, do provide heavier loadings than those we have generally been designing for up to the present time.

Senator COOPER. The Department of Transportation recommended, or as I understand at least did not object to, the change in the permissible load limits. If I remember, 20,000 pounds

Mr. TURNER. 20,000 and 34,000.

Senator COOPER. For single axles and 34,000 pounds for tandem axles.

Mr. TURNER. Yes, sir.

Senator COOPER. Would the present structures on the Interstate System be able to carry that increase satisfactorily?

Mr. TURNER. Yes, Senator Cooper; they will carry them but the result is that they produce some greater stress in the structure that had been originally designed. They produce overstresses in certain members of our bridges in the order of 32 to 36 percent higher than the design stress, but

The CHAIRMAN. Is that an immediate danger or is it just one which diminishes the life of the bridge and the safety factor?

Mr. TURNER. It will produce no immediate danger of collapse or structural failure. Bridgès are characteristically designed with very heavy safety factors and they will stand much greater overstress than the figures I have just given to you but the long-term life may be affected rather materially because repeated overstress beyond that for which the member was designed will result eventually in a shortening of the life of the member and that shortening due to fatigue is in a ratio considerably greater than the increase in loading that you mentioned, 34,000 pounds for tamdem axle compared to 36,000pound tandem axle.

Senator COOPER. Mr. Turner, are you able to provide any information as to the consequent result on these bridges if the tandem axle load were increased to 36,000 pounds, as S. 2658 now proposes?

91-955-68-2

Mr. TURNER. I think, Senator Cooper, if I might, I prefer to furnish you some material for the record at this point in order that I might be more precise in the figures. In generalizing, there is a reduction in the life of a member through fatigue action which in certain members might be as much as 60 or 70 percent reduction in the number of overstress cycles to which that member could be subjected without damage.

As you increase loadings and thus increase the number of stress overloadings, you reduce rather rapidly the life of that member from fatigue factors.

Senator COOPER. That involves both maintenance and the safety factor.

Mr. TURNER. Yes. You would not be able to maintain this member. The fatigue factor would be there regardless of any maintenance that you might do. There is no maintenance effort that could be applied to the bridge which would offset this overstressing and this fatigue factor.

Senator COOPER. Would that mean then, logically, that from the time you got the weight increase it would call for reconstruction of a substandard bridge to meet the additional stresses?

Mr. TURNER. Yes. It theoretically has the effect of shortening the life of the structure and advancing the date on which theoretical failure of the structure would occur.

Senator COOPER. I assume, though, that so far as construction of bridges in the future is concerned, whatever increase in maximum weights is adopted would require that those bridges be constructed in such a way as to meet the additional stresses.

Mr. TURNER. Well, we are not designing at the present time the additional safety factor that you are referring to; we are designing on the basis of the current loadings as stated in the design guides of the American Association of State Highway Officials which we have adopted in the Bureau. Those, as I say, do have a considerable safety factor built into them but going to the higher loadings that are proposed in the bill that the committee has been considering does eat into and consume part of that safety factor which we have designed into the structures.

Senator COOPER. You have discussed in your testimony the bridges that have already been constructed. I am asking you now, if the Congress should adopt legislation which permits the States to go to higher load factors, would it not be required-as a matter of safety and of system like and maintenance as well-that the Bureau of Public Roads then develop new standards for bridges to carry these new load limits?

Mr. TURNER. We obviously would have to, Senator Cooper, but this does not take care of the structures that we have already built. Senator COOPER. I know that. But would those new bridges cost more I mean just on the factor of designing for heavier stress, not cost increases of other kinds which may occur? Would it require the design of bridges which would be more costly simply because of the heavier loads to be carried?

Mr. TURNER. Yes; they would increase in cost, Senator Cooper. Senator COOPER. Ninety percent of that cost would fall on the Federal Government, and 10 percent on the State?

Mr. TURNER. Yes.

Senator COOPER. With respect to the existing bridges, would the total cost fall upon the State governments?

Mr. TURNER. The effect of the question would be that it would fall entirely upon the State because it would come into the cost of maintenance and the earlier replacement of that bridge.

Mr. BRIDWELL. Senator, I just wanted to interject one thought, if I may, sir.

Your questions have been in reference to the Interstate System? Senator COOPER. Yes.

Mr. BRIDWELL. I think it is quite important that throughout the whole history of our consideration of weights and size policy we at many times tried to address ourselves to the question of whether you can in fact have different weights and size policy for different kinds of highways and each time we have concluded that the problems of enforcement, the assurance of different weights and sizes on different highway systems are of such a magnitude that, as a practical matter, a weight and size policy almost has to apply to all road systems.

Senator COOPER. I believe that, too. That is what I come to next. The size and weight bill before the committee refers only to the Interstate System; that is why I just spoke of bridges on the Interstate System. As a practical matter, though, an increase in maximum weights would also affect the primary and secondary road systems, because the tracks go over them.

Now, I am going to close with this. I would assume that the same problems which you have raised with respect to bridges on the Interstate System would be applicable also to bridges on the complete Federal system-in fact, bridges on any road system.

Mr. TURNER. It would probably be more applicable, Senator, because on the other than the Interstate System our bridges have generally been designed for lesser loadings than those I mentioned for the Interstate System.

In fact, I believe we probably have a majority of our bridges on the Federal-aid primary and certainly on the secondary system that are less than the so-called H-15 design loading and thus the overstressing of those bridges would be much greater than the figures I referred to for the interstate.

Offsetting that to some extent, of course, is the fact that the number and frequency of heavy truck loadings on those bridges is obviously much less in most cases than it is for the Interstate System because the Interstate System does carry the bulk of the vehicle miles of heavy truck travel, as you know.

Senator COOPER. Are you able to give the committee at this time. or provide for the record any estimate or true number of the bridges which are on the Federal systems, apart from the Interstate System?

Mr. TURNER. Yes; we can give you information of that kind. I do not have it with me this morning and I do not have in mind the precision I would like to give it to you. If you wish, I will furnish it for the record at this point.

Senator COOPER. Mr. Chairman, I would like the Bureau of Public Roads to provide the committee information for the record which would go to the additional stresses placed upon these different types of bridges by an increase in the load limits, first to the 34,000 pounds tandem axle and then the 36,000.

Senator Spong (presiding). All right, sir.