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Road Engineering Journal
Copyright © 1997 by TranSafety, Inc.
November 1, 1997
TranSafety, Inc.
(360) 683-6276
Fax: (360) 335-6402
transafety@live.com

Maintenance Considerations in Highway Design

It has been long recognized that those who design highways have given inadequate consideration to the maintenance problems that are related to many designs. Aging facilities, greatly increased traffic volumes, tighter budgets, and limitations on staff have only served to compound the problems associated with maintenance. The National Highway Research Program (NCHRP) Project 14-9 (2) was initiated in response to the need to develop a routine process to improve communications between designers and maintenance personnel during the design process. The obvious goal would be to minimize the impacts on maintenance over the expected life of the facility. NCHRP Report 349 "Maintenance Considerations in Highway Design" presents the results of this research project.

Part of this report addresses highway design features, including policies, roadways, drainage systems, appurtenances, and roadside elements. The specific maintenance problems related to these features and suggested solutions to these problems are summarized here. It is important to note that these recommendations have been reached through a research approach that included literature review, a survey of practices, interviews with selected state transportation agencies, and, in some cases, demonstrations.

In incorporating any of these suggestions or designs, agencies must first consider safety laws, regulations, guidelines, and any other design requirements in effect. The processes described here should serve as guidelines for individual jurisdictions and at the very least provide for better communication between design and maintenance personnel. (NCHRP Report 349 contains more detailed explanations of the various recommendations listed and also provides a summary of the participating states' responses to the questionnaires concerning maintenance and road design.)

POLICIES

According to Report 349, consideration of maintenance should begin early, during the location studies, and continue throughout the design process. Highway geometrics have a substantial impact on maintenance requirements. Erosion control, which generates a large portion of maintenance expenditures, can be minimized by proper location and geometric design. Access and right-of-way availability also contribute to ease of maintenance. In any case, policy should include the following design considerations:

  1. Investigate geology and geotechnical features to avoid or minimize potential problems (i.e., rock slides, highly erosive soils, unsuitable materials).
  2. Maximize southern exposure in mountainous and hilly areas to minimize snow and ice accumulation. Allow space with proper drainage for dumping or storing plowed snow.
  3. Give careful attention to adequate drainage needs and protection from flooding, because the maintenance of drainage elements is a major cost item.
  4. Consider access requirements for maintenance and rehabilitation in all aspects of highway location and design.
  5. Avoid horizontal curvatures which incur more maintenance due to runoff from melting snow and ice and avoid sag vertical curves which may cause water ponding if drainage systems get clogged.
  6. Consider maintenance needs in establishing right-of-way limits and fence locations. Consider the purchase of additional right-of-way to flatten short sections of high embankments so that they can be maintained more easily.
  7. Conduct a value engineering analysis to compare embarkment sections having flat slopes and wider right-of-way with sections having steeper slopes or retaining walls, or both. Include maintenance costs in analysis.
  8. Consider the maintenance facility requirements (i.e. yards, pit sites, snow storage, waste areas).

ROADWAYS

Roadway features include mainline and ramp pavements, shoulders, medians, islands, and embankments. Since pavement maintenance and rehabilitation consume a large part of maintenance expenditures, roadway designs should incorporate the following considerations:

  1. Provide adequate subgrade drainage, minimize loss of fine material and clogging of the subdrainage by wrapping filter fabrics around french drains or underdrain pipes, and outlet drain pipes into paved ditches or culverts.
  2. Provide skid-resistant surfacing in wet climates.
  3. Consider future pavement resurfacing requirements when establishing vertical clearances and designing elements such as inlet grates and manhole covers.
  4. Consider the use of longer pavement life and PCC pavement in congested urban areas. Maintaining traffic flow during rehabilitation is costly.
  5. Consider the full use of full pavement design from shoulder to shoulder in urban areas and omit troublesome joints between pavement and shoulders. Full pavement design is an expensive solution and should only be used in heavily traveled urban highways. Other roads should consider extending the pavement structure at least 2 to 3 feet.
  6. Consider paving area under guardrails to minimize vegetation control problems.
  7. Provide a shoulder sloping away from the pavement on the high side of superelevated sections to prevent icing conditions on pavement due to melting snow deposited on the shoulder.
  8. Create a contrast between asphalt pavement and asphalt shoulder by applying stone chips to the shoulder surface. A slotted pipe would help prevent clogging from loose stones.
  9. Avoid the use of unpaved narrow medians or small traffic islands. Maintaining grassy areas is difficult, dangerous, and costly.
  10. Consider offsetting concrete barriers (if median is 22 feet or less) to increase shoulders and allow safer parking of maintenance vehicles.
  11. Provide flat slopes and rounding to minimize erosion potential and to make maintenance operations easier.
  12. Consider providing benches in higher cut slopes to collect debris, to slow runoff, and to collect water from slope pipes. Access for maintenance vehicles should be provided.

DRAINAGE SYSTEMS

Maintenance problems related to drainage are costly expenditures. Constant attention must be given to controlling erosion in ditches, cleaning culverts and stormwater systems, repairing eroded and scoured outlet areas, controlling corrosion, and repairing damage due to frost and clogging. In planning drainage systems, designers should consider the following strategies:

  1. Select vertical and horizontal alignments of culverts so that inlets and outlets are close to existing channels--thus preventing sediment or erosion.
  2. Base selection of pipe and culvert materials on evaluations of acidity, resistivity, chloride, and sulfate levels in the soil and water. Abrasion of culverts depends on the flow characteristics and materials carried by the stream.
  3. Size culverts to allow passage of debris and provide for access by maintenance equipment for periodic cleaning.
  4. Provide a full or partial headwall to anchor pipe subject to uplift due to scouring and buoyancy and provide energy dissipaters at the outlets where scouring and erosion are possible. Access for maintenance at the outlet is also necessary.
  5. Provide access to ditches along the highway where maintenance vehicles can cross easily and ditches are strong enough to support the equipment. Proper functioning of ditches is essential to convey surface water out of the highway right-of-way.
  6. Provide the appropriate ditch grade to minimize the possibility of erosion or sedimentation.
  7. Provide inlets in grassed medians and in curbed sections to eliminate ponding. All inlets should be combined with curb openings if debris accumulation is a problem.
  8. Avoid the use of curbs to reduce danger to traffic and damage to snow removal equipment.

APPURTENANCES

Appurtenances also demand a large share of the maintenance budget. Traffic, vandalism, animals, and atmospheric conditions cause the most damage to these elements. Their maintenance and repair are labor-intensive. Substantial cost can be saved if they are designed and built to be safe, durable, and easy to maintain.

Appurtenances can be classified into two main categories: roadway appurtenances which include barriers and guardrails, glarescreens, pavement markings and markers, rumblestrips, and attenuators and roadside appurtenances which include signs, lights, delineators, sound walls, and fences.

Roadway Appurtenances

The best way to design a highway is with minimal need for barriers and guardrails. Several other options can be used to protect vehicles in run-off-the-road situations:

  1. Use concrete median barriers in narrow medians to redirect vehicles parallel to the travelway.
  2. Consider using a concrete barrier as a combination barrier and glarescreen by extending its height.
  3. Consider designing a water-conveying median barrier to facilitate cleaning the catch basins under the barrier.
  4. Consider the use of open guardrail design in areas subject to snow or sand accumulation.
  5. Provide wider medians or lighting to eliminate the need for glarescreens and to reduce construction and maintenance costs.
  6. Use materials that are the least prone to vandalism.

Because pavement markings and markers wear from traffic, snow plows, sanding, and atmospheric conditions, maintenance is constant and, therefore, costly. Many jurisdictions recommend the use of epoxy, thermoplastic material, or precut tape in place of paint. Standard paint may be cheaper initially, but it does not withstand heavy traffic and harsh weather conditions. Raised pavement markers provide good visibility and have a long life span in non-snow areas. A grooved system with recessed pavement markings can be used in snow-plow areas. In some situations, depressed rumblestrips should be considered in place of raised markers.

Attenuators are used in places where hazardous fixed objects cannot be avoided-- such as bridge abutments, bridge rails, and sign posts. An ideal attenuator is durable and can easily be brought back to its original condition and position with inexpensive and available replacement parts. Consider the needs of snow removal and storage when using an attenuator, and make sure it does not create a hazardous condition on the adjacent lanes immediately following a collision.

Roadside Appurtenances

Roadside appurtenances should be placed with maintenance access availability. Major maintenance requirements include painting, cleaning, replacing, and servicing fixtures of lighted signs and repairing or replacing support posts damaged by crashes or deterioration. Vandalism is a serious problem and demands serious maintenance efforts. Locate signs so that guardrail requirements are minimized, access is easily and safely available, visibility is not inhibited, conflict with landscaping and other highway elements is avoided, and vegetation control operations are not hampered.

Lighting improves visibility at night and thus greatly contributes to traffic safety. Maintenance requirements include cleaning, relamping, repairs, and replacement. Sound walls and fences provide for protection and improve maintenance, but both require repair or replacement due to vehicular crashes, deterioration, vandalism, rock slides, etc. Roadside maintenance problems include managing vegetation growth by mowing or chemical application, collecting debris and litter, minimizing the adverse effects of deicing chemicals on turf and trees, controlling erosion, and repairing the results of vandalism.

CONCLUSIONS

Although "maintainability" should have a high priority, the goal in highway design is to reduce the costs of maintenance and construction and to obtain the maximum benefit from highway expenditures at the minimum cost over the expected life of the project. Of course, the drivers who use the roads cannot be ignored. The impact of these operations on the highway user is critical, and highway maintenance processes must accommodate the ever-present effect of traffic. In every maintenance situation, safety and accessibility are important considerations for everyone involved.

Copyright © 1997 by TranSafety, Inc.



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