OIL SURFACED ROADS TEST SUBGRADE FOR FUTURE SURFACES

How good is an oil road? Has it a distinct value? What is its economical life? When acid, what should be the next step?

Arizona now has many miles of oil roads. The traveling public thinks they are wonderful. The ease with which traffic whisks over them establishes a mental inclination which causes the people to urge the continuation of their construction. Once a rough dusty high way is made smooth and clean by oil surfacing, there is little wonder why failures because of faulty drainage, faulty sub-grade or faulty material. In either case the failure should be corrected if traffic is to continue uninterrupted. Up to date forces have been able to handle this sitation successfully in nearly all cases. The placing of oil surfacing on a road under ordinary traffic is a fair, but not an absolute proof of the value of the subgrade upon which it is placed even though we know that the oil surfacing is of good quality and properly constructed otherwise. During the life of the oil of traffic and if properly maintained proven the quality of the subgrade. It has forced certain requirements necessary to modern traffic, but the time of its usefulness is but a few years and from an economical standpoint, it is doomed to give way to a replacement or added waering surface as a public demand.

It is not the intention at this time to go into the details of comparison of the different types of road surfacing and pavements. In fact it matters but little to the traveling public just what the highway is surfaced with so long as it is an all-season, smooth-riding roadway and if maintained properly the cost of construction is merely a matter of record.

An oil surfaced road like other smooth types of surfacing and pavements invites traffic when placed on our main highways and it is not long until maintenance costs of the oil road begin indicating that the original construction is the first stage of a more permanent type of road.

A road is no better than the subgrade, but the subgrade is not the only part of a road which can cause success or failure. Surface failures originating from causes other than poor subgrade are numerous and steps should be taken to prevent them. Subgrade failures are often times latent in character and yield stubbornly to corrections and the opinion here is that an oil surfacing placed upon any roadway will reflect the good and bad qualities of the subgrade more quickly than any other types of surfacing. This fact is one of the distinct values of an oil surfaced road and the public craves for more of the same kind of improvement.

Dusty roads are dangerous and expensive in many ways. Old surfaced roads take out many hazards, but in turn add others. A clean smooth surface naturally superinduces faster and less careful driving. This obviates the necessity of safe widths, profiles and curvatures along with ample caution signs and guard fencing. In other words the use of a road after being oil surfaced will point out to the engineers certain advisable requirements before the adoption of a more expensive type of construction. An oil surfaced highway is a vast improvement over the ordinary surfaced highway, and while it is serving a wonderful purpose in regards to transportation, it is in fact the pioneering forerunner of a higher type hard surface pavement which is sure to follow.

With the hard surface pavement in mind the oil surfacing has a distinct value. Traffic is increasing each year and the weaker parts of the road get no favors except from the maintenance department. The weaker portions might surfacing which will vary with the amount of traffic, the maintenance forces will have corrected all of the major weaknesses in the subgrade and general routine maintenance will continue. But the point of fatigue is sure to come even with increased maintenance allowance. Up to the time of apparent approaching fatigue the oil surfacing has been a useful and splendid improvement and a good and economical investment. It has facilitated the movement

By GEO. B. SHAFFER, District Engineer. Reflects Quality of Subgrade Faults in Grade are Detected