From Engineering Policy Guide
Shoulders parallel the roadway surface and extend to the outer edge of the roadbed. They are used by traffic in an emergency but they are primarily constructed to afford protection to the roadway surface, to give the roadway lateral support and to give some measure of protection to traffic. Shoulders are to be maintained reasonably smooth, free of holes and ruts and slope away from the pavement edge to provide surface drainage. They should be kept level and flush with the pavement at the pavement edge. Width is to be maintained as constructed unless it is desirable to widen the shoulders during normal ditching operations. Refer to the Maintenance Planning Guides for Shoulders for additional information and best practices.
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Shoulders are generally one of the following types:
1. Earth and sod shoulders.
2. Aggregate surfaced shoulders with variable amounts of gravel or crushed stone.
3. Stabilized aggregate shoulders on which a prepared thickness of stabilized aggregate has been placed with no surface treatment.
4. Bituminous surface treated shoulders normally placed on a prepared flexible base. This base may consist of rolled stone, stabilized aggregate, soil cement, or asphalt stabilized aggregate. The thickness of this base will vary. The surface treatment may be a seal coat or prime coat. Prime coats are sometimes referred to as "color" coats and these are usually placed to provide for delineation or color differential. A wedge or ribbon of asphaltic concrete or bituminous material may also be in place adjacent to the pavement edge.
5. Bituminous paved shoulders include those surfaced with a bituminous material, usually on a prepared base or subgrade. On some roads, this shoulder paving is an extension of the roadway surface paving. On these sections, the shoulder may be seal coated to provide delineation.
6. Concrete paved shoulders constructed with Portland cement concrete. These are normally found in urban areas where conditions warrant this type.
Earth shoulders consist of those shoulders where turf has not been significantly established. Earth shoulders require extensive maintenance, especially in the period immediately after construction. Every effort must be made to establish turf and to protect any turf present, in order to prevent erosion, and the resultant loss of soil.
Where turf is attempting to establish itself; ruts, holes, settlements, and erosion should be corrected by the addition of soil rather than by continuous blading. Light spot blading will not be harmful if done at the proper time and if controlled closely. Fertilizing, reseeding, and spot or strip sodding may also be desirable.
If erosion, rutting, or settlements are extensive, the shoulders should be reshaped by blading and a slope of one-half inch per foot from the pavement edge, obtained. Shoulder edges shall not be cut down or the shoulder width decreased to obtain any additional soil. Additional soil, if needed, can often be more advantageously obtained from borrow areas or excess material purchased from quarries.
Repeated bladings of backslopes and ditches results in erosion of top soil and destruction of turf. Reshaping or heavy blading of shoulders shall be done in early spring when ground conditions are moist but not too wet. Extensive blade maintenance in the fall or winter results in a soft, hazardous shoulder during the wet season. After the desired cross section has been obtained, the shoulders and affected areas should be harrowed, fertilized, seeded, and rolled lightly.
Earth shoulders on the inside of super elevated curves and on steep grades are difficult to maintain. These areas may be surfaced with aggregate to reduce the amount of maintenance required. Earth shoulders on major routes with heavy volumes of traffic may be considered for upgrading to aggregate surfaced shoulders. In general, two tons of aggregate per station for an eight foot wide shoulder will provide some stability. The placement of a 2 to 4 ft. wide strip of aggregate along the pavement edge has also proved effective where shoulder settlement is continuous or edge ruts are a problem. This strip should be placed with a minimum depth of 2 to 4 in. at the pavement edge.
Light blading and rolling of earth or sod shoulders in the early spring is very effective, but this should be done after all frost is out of the ground. The use of tractors with rear mounted blades in conjunction with a motorgrader provides for more economy when light blading shoulders.
Particular attention is to be given to the shoulders of routes that have been resurfaced through programs such as the maintenance "Contract Leveling Course" where the contract does not include shoulder work. The shoulder should be brought to a level flush with the pavement as soon as practical, which often involves hauling dirt from borrow areas, or obtaining waste materials from quarries and/or obtaining crushed stone for shouldering.
Since dirt or mud on the pavement could cause accidents, every precaution should be observed during shouldering operations to keep dirt off the roadway surface as much as possible. All dirt should be removed from the surface by light blading and brooming at the end of the day's operation. Since soil and weather conditions have a direct bearing on how difficult this removal of dirt from the surface becomes, effort should be made to schedule this type of work during ideal weather conditions. During the course of the operation all required traffic controls should be used and if any semblance of dirt is still on the surface after the day's work, the appropriate signing should be left up over night.
Sod shoulders are earth shoulders on which a solid turf has been established. Normally they require very little maintenance and holes, ruts, and settlements should be repaired with sod or stabilized material. Hand labor with shovels is an effective method of smoothing up ruts. Light blading, if necessary, should be done in the same manner as for earth shoulders. The buildup of turf over a period of years, sometimes presents a drainage problem and when this buildup prevents adequate drainage from the roadway surface it should be cut off. Light blading or cutting at more frequent intervals is recommended over heavy cutting, which will usually destroy the turf. Trenching laterally across the shoulder to provide drainage shall not be done as the trench will be a definite hazard to traffic.
Aggregate surfaced shoulders will vary in thickness, which will affect the amount of maintenance required. Where the aggregate surfacing is light, turf will be established to some extent and should be encouraged to provide additional stability and to prevent erosion. On these shoulders blading should be held to a minimum and spot repairs made by the addition of aggregate. Aggregate surfaced shoulders with an appreciable thickness of aggregate should be bladed periodically to keep the surface flush and level with the edge of the pavement. Blading should be done immediately after a soaking rain to prevent segregation of larger sized aggregate and the shoulders rolled after blading is complete. It may be desirable to upgrade aggregate surfaced shoulders at problem spots and in urban areas.
Surface Treated Shoulders
Prime coated shoulders (color coated) may be changed to a seal coated shoulder, if conditions warrant, with the exception that the test section shoulders are not to be sealed and must continue to be maintained as a prime coated shoulder.
Seal coated shoulder surfaces require continual attention and shall be spot sealed, spot patched and base failures repaired with methods similar to roadway surface maintenance. It is imperative that this work should not be neglected. The need for continuous seal coats or fly coats shall be based on the surface condition or anticipated conditions and not to provide color contrast alone. Fly coats sometimes referred to as fog seals consist of a light application of cutback or CSS1-H or SS1-H emulsified asphalt, normally 0.1 or 0.15 gallons per square yard, to the surface. The emulsion is diluted as per the manufacturers recommendations. RC-70, CSS-1 and SS-1 have proven effective and will not require blotting if done at the proper time and rate. Fly coats will restore life, prevent oxidation for some period of time, seal fine cracks and is economical. If oxidation or deterioration has progressed to the point where a fly coat is not practical, a seal coat should be considered.
Prime coat shoulders deteriorate rapidly on the surface but this failure is not too critical except at the edge of the pavement. Spot fly coating may be done but if base failures are also involved it may be best to light blade and roll such sections until they are stable and then apply a new continuous prime coat. Additional base material may also be placed as necessary to correct excessive settlements or failures.
All preparatory work necessary on surface treated shoulders shall be accomplished prior to the application of continuous seal coats or fly coats. This preparatory work may consist of sealing the edge joint, wedging, strip sealing, spot patching and spot seal coating.
Repairs to bituminous or concrete paved shoulders should be in the same manner as for similar roadway surfaces. If a seal coat has been placed for delineation, it shall be maintained as a seal coat surface.
Shoulder Edge Ruts and Settlement Maintenance
Edge ruts are a continual maintenance problem on earth, sod, and aggregate shoulders especially where roadway surfaces are less than 24 ft. wide. They are caused by the sweeping and vacuum action of vehicles and vehicle tires, by vehicles running partially or completely off the roadway surface and by erosion. Edge ruts are usually not a problem on surface treated or paved shoulders. Settlement of shoulders, with a resultant drop off at the roadway edge, is caused by the difference in stability between the roadway and shoulder. Once identified, the maintenance of edge ruts and settlement should be accomplished as soon as practical during normal working hours.
Maintenance of Edge Ruts
Edge ruts can be helped by filling the rut with aggregate, soil, sod or other material. The material should have stability to prevent rapid recurrence of the condition. The material may be light bladed in from the shoulder or hauled in a hopper bed and applied from the hopper bed with the fan removed. Spot sections can be filled by hand labor. The material should be compacted thoroughly. A windrow of material shall not be left along the edge for traffic to compact. Repeated applications of aggregate and asphalt similar to penetration macadam methods have also proved effective in repairing edge ruts as the asphalt serves as a binder. Bituminous mix material is not recommended on lower type shoulders unless it can be placed to sufficient depth or on a base to prevent breakup. Sections that require continual maintenance, such as on the inside of curves should be cut down, base material placed and the surface paved with bituminous mix.
Maintenance of Settlements
Shoulder settlement resulting in a drop off at the edge of the roadway normally involves settlement of the entire shoulder width to some degree but restoration full width is not always necessary unless the settlement is excessive.
Settlement on earth, sod and aggregate surfaced shoulders is normally corrected by blading shoulder material into the edge of the roadway and compacting. The addition of material full width or aggregate placed in a two foot wide wedge along the edge may also be used.
Settlements on surface treated shoulders may be corrected by strip sealing, twelve to twenty-four inches in width, if the settlement is minor or less than one-half inch. For settlements of one-half inch or more, a bituminous mix wedge one to two feet in width should be placed. A fine graded high type mix should be used and a sled type hopper, fed from a dump truck bed, or similar methods have proven very efficient for placing this wedge. If a hopper is used, it should have a strike off blade which can be adjusted. The wedge is placed flush and level with the pavement and tapered on the outside edge. Compaction may be done with truck tires and steel wheel rollers and material must be kept off the roadway surface by sweeping. Excessive full width settlements can be corrected by patching with a bituminous road mix. Road mix is desirable because of economy.
Edge Joint Maintenance
Sealing or filling the joint between the pavement edge and stabilized surface treated shoulders is of primary importance to exclude water. Refer to Joint and Crack Maintenance - Edge Cracks.