Drainage cannot be emphasized enough in road construction and maintenance. Water affects the entire serviceability of a road. Too much water in the base materials weakens the road. Water allowed to remain on top of a gravel or paved road weakens the surface and, when combined with traffic, causes potholes, cracking, and rutting. If improperly channeled, water causes soil erosion and breakdown of pavement edges. Whether it's mud in the spring or frost heaves in winter, the presence of water in roads is nothing but trouble.
Building and maintaining a good surface drainage system and maintaining it is the best way to lessen water's damaging influence on a road. A proper surface drainage system prevents water from infiltrating the pavements surface and removes water from the driving lanes in a constant thin sheet to the side ditches which carry the water away from the roadway. Sealing cracks in the pavement surface also helps but this is of little use if the surface drainage system does not function properly. A surface drainage system has four components: road crown, shoulders, ditches and culverts. The crown or super-elevation of the road surface allows water to run off to the side ditches.
Shoulders are an extension of the road surface and allow for the continued flow of water to the ditches. Ditches are used to carry water away from the roadway. They need to be kept clean and protected from erosion. Water left in the ditch can sometimes leak back into the pavements foundation materials. Water collected and carried in the ditch has to be directed away from the roadway at frequent intervals sometimes using culvert pipe. Culverts usually channel water from one side of the road to the other, helping to control the flow of water and slowing it down to reduce erosion.
Road managers are guided by the principles that 1. water runs down hill, 2. water needs outlets at the bottom of all grades, and 3. puddles mean problems. If it were not for water, a road commissioner's job would be easy. But because of water, whether in liquid form or as snow or ice, a road manager's work is never done. Except for some moisture that is needed for soil compaction and for dust control, water is the road manager's enemy.
2. Build on a Firm Foundation
A highway wears out from the top but it falls apart from the bottom. This is another way of saying that the road base determines the service life of a road. The base supports everything above it including traffic. If adequate support does not exist, the road will rapidly deteriorate. A good road requires a suitable foundation which, in turn, requires stable material. A road material is stable if it has little or not change in its volume and does not deform under repeated loads whether the material is wet or dry.
Soils can be stabilized using such agents as asphalt, calcium chloride, cements, lime, salt and other products. To select the proper stabilizing agent, an understanding is required of both the soil and agent to be used. The additive must be of the correct type and in the correct quantity to produce satisfactory results. Geotextiles may also be very helpful to stabilize a soft road.
3. Use the Best Soils Available
In Maine, natural good-quality gravel is getting to be in short supply. Blended or crushed gravels are more expensive alternatives. The quality of soils used by a town will often depend on local availability and budget. In deciding what is affordable, a town should consider the long-term consequences of using lower quality material. By putting down a good base in the beginning using quality materials, a town can correct the few weak spots in the roads over a period of years and be assured of a sound base upon which eventually to apply a permanent hard surface.
Using inferior base materials may require excessive maintenance during the road's life and perhaps costly rehabilitation before paving. The adage "pay me now or pay me later" applies to road building.
Written guides exist to help road commissioners classify the usefulness of soil types for road foundations and bases. The guides give information on potential frost action, compressibility, and drainage characteristics.
4. Compact Soils Well
The denser the materials, the stronger the base. When soil is improperly compacted, future traffic loads or changes in moisture content can cause settlement and failure of the roadway. Compaction is achieved by pressing soil particles together using rollers, tampers, or vibrators, expelling the air from the mass, filling the spaces between the particles, and making the material more dense.
Well-graded soils having a fairly even distribution of particle sizes will compact more easily than poorly-graded soils having mostly one particle size. Jagged or semi-jagged particles will compact to a more stable configuration than rounded particles of similar size. A certain amount of moisture is necessary for good solid compaction.
5.Design for Winter Maintenance
If a town designs its roads for winter maintenance, they would be adequate for the remainder of the year. Consider the following:
- A one-way plow cuts a nine-foot-wide swath. If the road is wide enough to allow the plow and a school bus to meet, it is wide enough during the remaining seasons of the year.
- If ditches and roadside areas are wide enough to store snow, chances are they will accommodate spring thaws and heavy water flows.
- A town will not be sorry for having a wide road but it may regret building a narrow one.
- Grades should be a minimum of one percent for drainage purposes but should not be greater than ten percent, if at all possible. If the road is steeper than that, it is difficult for heavy equipment to maneuver, especially in wintertime.
- Sight distance should be considered in designing a road. For safety's sake, a driver should be able to see 75 to 100 feet up the road for every 10 miles of speed. This rule of thumb may be helpful when issuing permits for driveways onto a town road.
6. Build for Traffic Loads and Traffic Volumes
Ice on a pond will support a young skater but it will crack under the weight of an automobile or even break apart. Similarly, a road built to serve residential traffic will break down when it starts carrying a number of large trucks. It takes the passage of approximately 9,600 cars to equal the effect on a road of the passage of one 80,000-pound truck. Road commissioners know that roads, like bridges, should be designed with the expected traffic type and volume in mind.
A rule of thumb is to design a road to accommodate the largest vehicle, which will use the road under normal operations. Designing the road for the largest piece of town equipment which maintains it in all kinds of weather may suffice. To determine the required depth of base, a common guide is to put in ¾-inch to one inch of gravel for every foot of traveled way width. For example, a 20-foot-wide roadway should have a minimum of a 15- to 20 inch gravel base.
When considering the type and thickness of pavement mixes to apply on a gravel road, a town is wise to seek some advice. Generally speaking, a low-volume road (300 vehicles per day or less) having some truck traffic may provide good service with a "chip seal." The main function of such a seal is to eliminate the need to replace and reshape gravel, eliminate dust and to prevent raveling of soils. As traffic volumes and weights increase, the type and thickness of pavement should increase to a point where the pavement itself actually shares the load stress. Heavy-duty Interstate highways, for example, have a foot or more of asphalt concrete below the riding surface.
7. Pave only those Roads that are Ready
In their haste to put a smooth surface on a gravel road, some towns make the mistake of paving over a road that is not properly prepared. The result may be a complete waste of money. Unless the base of the road is first built with the proper thickness for the traffic it must bear and the gravel is compacted to a proper density with the ability to drain well, any pavement put on it will fail. Experienced road commissioners make sure a gravel road works well before paving. The cost of reconstructing a failed road is must higher than doing it right the first time.
8. Build from the Bottom Up
A road that has a poor base and poor drainage cannot be adequately improved with a top dressing of gravel or new pavement. It may be necessary in some cases to dig out the old road, put in new material and build up the road in layers. Before doing anything to correct a road surface problem, road managers take into consideration what is causing the problem underneath. Improper drainage, insufficient depth of base or poor quality gravel may be the culprits. These should be corrected before spending money on the surface.
9. Protect Your Investment
If worn roof shingles are not replaced and if the outside is not painted occasionally, a house will deteriorate and lose value.
Roads and bridges also need regular maintenance to keep them from deteriorating. The increased weight and frequency of traffic on Maine roads combined with our adverse weather conditions, means an increased rate of road and street deterioration. Regular road and bridge maintenance preserves our road investment and prevents costly major rehabilitation later on.
Maintenance activities include:
- Roadway Surfaces - blading and shaping, patching, resurfacing; dust control; snow and ice removal
- Drainage - cleaning and repairing culverts and ditches
- Roadside - cutting brush, trees and grass; repair and prevention of roadside erosion
- Bridges - channel clearing; repair of rails, decks and structure; cleaning and painting
- Traffic Services - sign maintenance
- Special Projects - restoration or improvements; emergency work such as removing slides, and repairing retaining walls.
10. Keep Good Records
Road commissioners know their roads like the back of their hand. Most of them are a walking history book when it comes to the road they manage every day. This knowledge is of little use, however, when the road commissioner is laid up or retires.
Good record keeping makes roadwork must easier for everybody. It's easier to draw up budgets and to show citizens plans for roadwork. Recording what type of work was done on a road or bridge, when, and what materials were used can help a lot in decision-making later on.
Towns can start by inventorying all roads and bridges, listing length, width, surface types, culverts, problem areas and other items. Putting these items on a map helps. Next comes listing and prioritizing needed improvements, putting a price tag on them and knocking off a few problems each year. Good record keeping of road and bridgework and equipment is good business. Several user friendly software programs exist to help towns in this effort, and are available at the Maine Local Road Center at 1-800-498-9133.