James C. Thomas
Sr. Research Associate, Soil and Crop Sciences Department
Texas A&M University
A major problem associated with living in the country is building and maintaining an adequate, all weather access route to your house, barn or other areas of your property. In most urban areas, where home sites are small and houses are located close to paved streets the driveways are short and generally paved with a durable concrete or asphalt surface. However, in rural settings, driveway distances may be very long, and paving with concrete or asphalt is cost prohibitive. That is why most rural driveways are often thought of as short earthen roads that receive light use and have little to no covering or topping.
Often, too little thought is given to the proper siting and design of rural driveways which leads to serious problems during periods of prolonged wet weather or times of heavy traffic. In most cases, the rural driveway is really a means of connecting two points: the house and the nearby public access roadway. Homeowners typically select the location of their house very carefully to achieve desired amounts of shade, specific views of the landscape, adequate ventilation, etc. An equal amount of consideration should be given to the location of the garage and home entrances. While it may be aesthetically pleasing to locate the garage in the farthest corner from the road; doing so may require the construction of an excessively long driveway which may cross areas that are poorly suited for traffic. Safety concerns must also be addressed in terms of the intersection of the driveway with the public road or highway. Issues including safe sight distances, proper turning radius, angle of intersection and vertical alignment all need to be addressed.
The objective of this publication is to help the reader think through all the necessary considerations for the proper planning and construction of a rural driveway which will be best suited for their individual situation. Since most of the final decisions will be dependent on the needs of the individuals involved, and on parameters specific to the site being developed; the discussion will primarily focus on which factors need to be considered, what decisions need to be made, and how best to make these decisions based on available information and resources. When possible, suggestions will be made to help guide individuals in obtaining outside help if needed.
Assess Your Needs
Assuming that this is an undeveloped piece of property, you as a land owner need to make a realistic evaluation of your future use of the property with respect to the number and size of vehicles that will be using the driveway. Will immediate family members be the only ones using the driveway or will you be receiving regular deliveries and pickups by large vehicles or semi-trucks? Will you be entertaining large numbers of guests at parties or having large family reunions at your home? Load bearing requirements, turning radius, and sight distances will all be different for passenger cars versus pickup trucks towing heavily loaded trailers versus heavy commercial trucks. How critical is it that you have access to all areas at all times or are there certain areas that do not require daily access? What financial commitment are you willing to make for the construction of a driveway?
Another consideration is parking. A sufficient area needs to be provided to park vehicles and equipment which will commonly be kept on the property. An ideal parking space for a typical auto is an area 10' wide by 20' long (Bushell, 1996). Remember to plan ahead for when teenage children may get vehicles of their own and bring them home as well. If you have elderly parents or relatives living with you now, or may have in the future, you need to plan for easy access to the home entrance. Even if easy access is not needed immediately, it may be needed in the future should someone suffer an accident or have an unforseen health related problem. The drive should be located so that it stops near the home entrance and there is a short unobstructed sidewalk to the house should someone with a walker or wheelchair need access. A minimum width of 36" is recommended for the sidewalk.
Remember to plan ahead for
The use of steps should be avoided if possible, since they cannot be easily traversed by wheelchairs. Plan for an area where a handicap accessible van can stop if necessary and pick up or discharge a wheelchair bound passenger. Overflow parking may be needed if you frequently get large numbers of guests for parties.
For safety sake, it is best if your driveway and parking area is designed so that vehicles can be driven forward out of the driveway rather than backed out onto a highway. This often necessitates either a circular drive or a turnaround area. Turnaround areas for most autos and pickup trucks can be easily located by starting at the back of the vehicle in the parking spot or from the garage door and drawing an arc having a 30' radius going in the direction of choice. This represents the path taken by the vehicle that will be backing up. Once in the turnaround area, the vehicle needs to be able to pull forward and exit the driveway without problem. Turnaround areas for large trucks or vehicles pulling trailers will need to be much larger and a 60' radius should be used.
Avoid having vehicles drive over sewer lines or near septic tanks to prevent crushing of the lines or a cave-in of the lid. Keeping the driveway free of vegetation helps keep the driveway well defined and avoids the problem of trying to mow grass in a very stony environment. This clean surface also allows for easy re-grading of the driveway surface when needed. However, a good stand of bermudagrass or other non-bunch grass may help bind the soil together and remove excess water via evaportranspiration.
Project Design and Layout
Selection of a suitable driveway location is paramount to having a successful project. A residential driveway needs to be a minimum of 10-12' wide and may range up to 20' across if it will be occasionally traveled by large trucks (Committee on Planning and Design Policies, 1960). Try to route your driveway through well-drained areas of your property. Since the driveway will have to support the weight of the vehicles that travel it, locate the driveway on high ground and avoid going through “marshy” or “boggy” areas of the property. These areas which stay wet much of the time have a much lower weight bearing capacity and have a greater probability of becoming future problem areas. When laying out the route for your driveway, keep in mind the direction of water flow and plan for a means of removing excess runoff water from the road surface and from adjacent areas.
It is recommended that you obtain a copy of the current county soil survey from your county extension office. Locate your property on the survey and identify the soil(s) which are on your property. In the beginning of each county soil survey, a description of each soil is given along with some summary tables indicating the general suitability of each soil for various uses. Usually, there will be a listing for “roads and highways” and/or “streets and parking lots”. Look at the information for the soils in these use classifications and you will get a general idea of what the major limitations are of the soils on your specific property. You may also visit the National Soil Survey Center.
Example of County Soil Survery
Soil Survey of Leon County, TX, authored by Conrad L. Neitsch, Joseph J. Castille, and Maurice R. Jurena, issued July, 1989, United States Department of Agriculture, Soil Conservation Service, in cooperation with the Texas Agricultural Experiment Station and the Texas State Soil and Water Conservation Board.
If your county does not have a recent soil survey, another approach is to dig a series of inspection holes along the intended driveway location. Each inspection hole should be 24" deep or at least 12" below the dark colored top soil. If the soil is gray below the upper top soil, this indicates the soil is water saturated for prolonged periods of time and may not be suitable for driveway construction.Entrance
As part of designing and laying out your driveway, careful consideration must be given to the intersection of the driveway and the public access road. The angle of intersection is commonly defined as the angle made between the centerline of the driveway and the edge of the pavement or the centerline of the public access road. If possible, it is preferred that a driveway intersect the main road at right angles (90 degrees) but intersecting angles in the range of 60-90 degrees are acceptable. Intersections at angles of 45-60 degrees may be used in special situations. Intersections at angles less than 45 degrees are strongly discouraged.
The second major consideration when planning an entrance is to consider issues related to visibility and having a clear line of sight. Safe entrance onto a public road is dependent on good visibility and the ability to detect on-coming traffic. Recommendations for visibility range from 130 feet for roadways with a 20 mph speed limit to 1,050 feet for roadways with a 60 mph speed limit.
Suggested Safe Sight Distances for Passenger Cars Entering Two Lane Roadways With Various Speed Limits1
Operating Speed (MPH)
Safe Sight Distance Left (ft)
Safe Sight Distance Right (ft)
1After Institute of Traffic Engineers (1974).
Larger and slower moving vehicles entering a public roadway will require longer sight distances. When possible, driveways should be located away from bends or rises in public roads that limit visibility. It may also be necessary to trim or cut bushes, trees or other vegetation both along the public road and your property to improve visibility. Visibility should also be considered when locating the placement of rural mailboxes.
Since many of the Texas public roads have fairly high speed limits, safety for stopped vehicles is a major concern. Therefore, careful consideration should be given to the installation of a short “ramp” or “siding” along the shoulder of the road where one may safely pull off the public road to get your mail without danger of being rear ended by a passing motorist. Your mail carrier will also appreciate such a ramp. If you intend to fence your property, the gate across the entrance should be set far enough back from the public road so that you can pull your vehicle safely off the road to a complete stop before the gate. Remember to plan extra room if you will be pulling trailers on a routine basis. Gates must be wide enough to accommodate large delivery trucks carrying whatever supplies you may be needing now or at some future date.
The third major consideration in planning a driveway entrance is the turning radius. The turning radius is a measure of the arc made as the driveway widens out and joins the public road. It is measured as an arc of a circle of a given radius. The general rule of thumb is that the turning radius should be between 5 and 20 feet for typical automobiles. Large trucks and vehicles pulling trailers typically make wide turns. Therefore, if you anticipate bringing these types of vehicles in your driveway, you should design your driveway entrance with a larger turning radius of 30-60 feet. The same turning radius applies to all other areas on your property where one may make a turn in the driveway such as when approaching the parking pad, garage or turnaround area.
The fourth and final major consideration in planning a driveway entrance is the vertical alignment of the driving surfaces. Ideally, your driveway surface, across its width, will be at exactly the same elevation as the public road so that there is no distinct “bump” as one traverses between surfaces. To prevent dragging of mufflers or hitting high center, it is also recommended that the driveway have a slope between 0 and 3.25 inches in ten feet (0-2.7%) either up or down to the public road. In no case should a change of greater than 6 inches in ten feet (5%) be used. This may require the placement and use of a culvert or similar device to allow the driveway to follow a relatively flat path to the road and avoid damages to the vehicles.
Other considerations in driveway design include consideration of the distance to the nearest neighboring driveway, lighting and surface material. If possible, driveways should not be located closer than 30-40 feet apart (centerline to centerline). Lighting the driveway entrance is helpful but not essential. Lighting and the use of a couple strategically placed reflectors on posts located on both sides of the driveway where it crosses the drainage ditches help drivers locate the entrance at night and during inclement weather. In addition, lighting will add some security to your location and will help improve the visibility of vehicles exiting the driveway. The use of a different colored driveway surface material as compared to the road surface, will also help distinguish the driveway area to passing motorists.
When soils become excessively wet, they loose much of their strength and load bearing capacity. Driveways should be slightly elevated above the surroundings and crowned to promote good surface drainage for optimal performance. Generally, the centerline of the driveway should be the highest point with a uniform slope of 0.5 inch per foot (4.1%) to either side. This will promote rapid runoff of excess water and minimize the amount of water which infiltrates into the driveway soil.
Driveways which are elevated above the surrounding soil will form barriers to the surface runoff from uphill areas and provision needs to be made to remove this water. Small drainage ditches should be used along the driveway as needed, particularly on the uphill side, to drain away excess runoff water which accumulates at the edges of the driveway. This will prevent the ponded water from weakening the driveway base, and possibly either flowing over the driveway or backing up onto adjacent property.
There will likely be times when it may be necessary to cross an area such as a natural drainage way or the drainage ditch along a public highway that occasionally carries water. The most common way to handle this situation is to install a culvert to allow the water to flow beneath the driveway. Culverts come in a variety of sizes starting at about 8 inches in diameter and ranging up to several feet in diameter. They are most commonly made of either corrugated steel, heavy gauge plastic, or reinforced concrete. The culvert needs to be sized properly so that it can carry the needed amount of water during periods of peak flow. The use of too small of a culvert will result in water ponding up on the entrance side and the potential for a wash-out of the driveway. Assistance in size selection and installation techniques can be obtained from the Natural Resources Conservation Service (NRCS), the local county highway engineer, the county commissioners, the county extension agent, the state highway maintenance superintendent, or a private reputable engineer. Computer programs for culvert design are also available for purchase from private companies. Some counties require that the culvert be sized and approved prior to the start of construction.
To prevent sedimentation from silting in and blocking the culvert, a minimum water flow rate of 2.5 feet per second is required. Slopes of 2-4% are ideal and a slope of 0.5% is the absolute minimum that is acceptable for use. Care must be taken to install the culvert on a smooth surface having a uniform slope to prevent the formation of low spots. Low spots will collect sediment and eventually plug up. The culvert should be long enough to extend past the backfill on the exit end so that the turbulent water exiting the pipe will not erode the edge of the driveway. Soil surrounding the culvert should be backfilled carefully in small amounts with tamping to prevent future settlement of this area. The culvert should be covered with a minimum of 6-18 inches of soil to prevent damage to the pipe from passing vehicles.
Culverts installed along county and state highways may need to be designed to meet specific minimum standards and be equipped with specific safety features. Therefore, contact your local county or state highway officials for this information prior to culvert installation on public highway right of ways.
Driveway Soil Materials
Undoubtedly, the first choice is to use the on-site soil for driveway construction. While this is obviously the most economical solution, in many cases the on-site soils may not be well suited for this use. Clay soils tend to get very slippery when wet while sands may become very soft. If your native soils are not well suited for use as a base material, they may be improved by the addition of an amendment. The addition of 5-10% Portland cement will cause the soil to set up into a hardpan or weakly cemented soil which will be better able to withstand traffic.
You may also want to consider the use of 10-15% fly ash, boiler ash, or other liming material from a nearby power plant or other industrial facility (Wong and Ho, 1989). If an amendment is used, it is important that it be uniformly mixed throughout the soil material. The amended soil should then be moistened, compacted immediately and allowed to set for 24-48 hours prior to applying a topping and being placed in service.
The ideal situation is to make a firm base for the driveway about 4-6 inches thick using the native soil, with or without an amendment, and then apply two inches of imported (purchased) crushed stone or rock as the final driveway surfacing material. Ideally, you should look for a topping material that is a mixture of fines and aggregate ranging in size from clays to aggregates as large as 1 inch in diameter.
Suggested Particle Size Distribution for Purchased Driveway Soil Materials1
Percent Passing (by weight)
1After Department of the Army (1957)
The mix should contain enough clay to bind the coarse aggregate together without becoming unduly soft when wet. After placement, the material should be compacted as firmly as possible. If possible, borrow or rent a roller or just compact it by traveling it numerous times with a heavy farm tractor. Try to compact all areas of the driveway equally rather than just compacting the areas where the wheels will normally travel. After some additional compaction by vehicle traffic, the material will make a firm, solid driveway topping. Your local NRCS agent, county commissioner or county engineers office should be able to help you locate suitable locally available materials.
Caliche based products are popular in many areas of central and west Texas. These materials are acceptable as driveway surface materials, but are rather dusty during the dry season. The drive may need occasional leveling or blading to maintain the desired slope and fill in any low spots. If the surface material becomes mixed with the underlying base material, you may need to occasionally add some additional surface material. If excessive dust becomes a problem, the surface can be sprayed with an asphalt emulsion to limit dust formation. Local highway and parking lot construction companies can provide this service.
In the future, if you decide to pave the driveway, the work which you have done in preparing the driveway will still be of value since it will serve as a firm foundation or base material for the finished driveway. The actual paving operation should be performed by a reputable firm specializing in driveway and road construction. This is a very expensive process and you should carefully enter into a signed contract with a reputable contractor in which you as the purchaser are provided with a specific written warranty and warranty period. Beware of out of town companies that have a “once in a lifetime deal” using some left over materials from a nearby highway construction job. As with most other trades, a deal that is too good to believe probably will not turn out to be what you wanted or expected and you will have little to no recourse.References
Bushell, F.W. 1996. Landscape by Owner: Driveways, Entries, Patios & Decks. One Leaf Publishing Co., Auburn, WA. 352 p.
Committee on Planning and Design Policies of the American Association of State Highway Officials. 1960. An Informational Guide for Preparing Private Driveway Regulations for Major Highways. 31 p.
Department of the Army. 1957. Roads and Airfields. Technical Manual 5-250. pg. 412-428.
Institute of Traffic Engineers. 1974. Guidelines for Driveway Design and Location. 47 p.
Institute of Traffic Engineers. 1987. Guidelines for Driveway Location and Design. 23 p.
Texas Transportation Institute. 1991. Recommended Design Guidelines for the Vertical Alignment of Driveways. Research Report 990-2. 44 p.
Wong, C. and M.K. Ho. 1989. Experimental Fly Ash Base Farm-to-Market Road 1093, Fulshear, Texas. Publ. by State Dept. of Highways and Public Transportation, Austin, TX 31 p.Acknowledgments
The input and assistance of the following individuals in the preparation of this article is gratefully acknowledged.
Dr. C.S. Anderson of Anderson Environmental,
Dr. F. Benson of Texas A&M University, Kingsville,
Dr. K.W. Brown of the Texas Agricultural Experiment Station,
Dr. R.L. Lytton of the Texas Transportation Institute, and
Dr. T.L. Provin of Texas A&M University, College Station, TX.