Highway alignment, road classification, pavement surface characteristics, cross-section components such as cross slope, varying road widths, and road margin features all have an impact on geometric design. The goal is to provide vehicles with enough space to stop safely while keeping traffic moving at a safe speed.
Alignment refers to the position of the road with respect to physical features such as rivers or lakes. A highway may be straight and level, following the contour of a hillside, or it may be curved with respect to other features. Curves can be gentle or sharp; they can also be open or enclosed. Roads that follow the contours of hilly land often have more than one curve in them. Alignment affects how wide the road should be and where traffic lights should be placed.
Classification refers to the type of surface being used on the highway. There are three main classifications: concrete, asphalt, and macadam. Concrete roads are made of broken up rock mixed with cement and sometimes sand. They are smooth and flat. Asphalt roads consist of crushed stone and tar mixed together. They are usually rough with irregular edges. Macadam roads are made of small stones glued together with clay or tar.
During the design stage, the best site, alignment, and geometry of a roadway are chosen. Highway design takes into account three primary aspects (human, vehicular, and roadway) and how they interact to produce a safe highway.
Human factors include the biological needs of drivers, such as the amount of sleep they need on overnight trips. Vehicular factors include the size, weight, and speed of vehicles on the road. Roadway factors include the type of surface, its width, curvature, and other characteristics. Designers consider all these factors when choosing what kind of highway should be built where.
Once a route has been selected, the next step is to determine the best location for bridges and tunnels. Tunnels require an entrance from one level of traffic control to another, so they must be constructed ahead of their use. Bridges are built first, then used when there is enough water under the road to float a bridge. Engineers use computer programs to design bridges before they are built. The software calculates the load that will be placed on each member of the bridge structure as well as the energy involved in moving this load over the bridge.
After the location of bridges and tunnels have been determined, designers choose the type of construction for the new road. Concrete bridges are by far the most common type of bridge, accounting for about 95 percent of all structures.
The geometric design of roads is a field of transportation engineering that is concerned with the placing of the physical features of the roadway in accordance with standards and limits. Geometric highway design is divided into three major components: alignment, profile, and cross-section. Alignment refers to the route a road takes between its origin and destination. A road's alignment can be straight, winding, or somewhere in between. The designer must consider local topography in choosing an alignment. For example, a road may need to wind through hills or along the edge of cliffs to reach its destination, so it should be aligned to take advantage of these features. The second component of highway design is the profile. The profile includes such things as the height and width of the road bed and the depth of the travelway (the area within the roadbed where vehicles travel). The third component is the cross-section. The cross-section consists of the shape of the space within the curb cuts and gutters on either side of the road. Traffic engineers use these terms to describe the various elements that make up the road geometry.
When designing a new road, the first decision that needs to be made is the type of facility that will be required. This will determine which of the many methods available for road design can be used.
Geometric design's fundamental goals are to maximize efficiency and safety while reducing expense and environmental impact. These goals are generally accomplished by choosing options for each element of the road design and then selecting among these choices to achieve a desired result. For example, one may choose between different types of surfacing materials or treatment methods for their surfaces.
Another goal is to provide clear communication through the use of sight lines and warning signs. The designer also seeks to accommodate other vehicles while keeping streets functional for other uses such as walking and biking. Finally, the designer aims to create a sense of place for both motorists and pedestrians by incorporating appropriate elements into their designs such as trees, benches, and buildings.
These are but some of the many considerations that go into the geometric design of highways. The main purpose of this course is to give you an overview of the field and help you understand how it relates to other areas of engineering and science.
Highway engineers are responsible for the design of all aspects of the road including its surface, sub-surface (if any), traffic barriers, sidewalks, curbs, ramps, and exit points. They must also consider environmental factors such as soil composition, drainage, and vegetation when designing roads.
The phases of highway engineering are as follows: * development, * planning, * alignment, * highway material, * traffic management, * highway geometric design and placement, * pavement design, * construction and maintenance, * economic considerations, * financial and administration.
Highway engineers have a wide range of practice in terms of project types from small local roads to large interstate highways. A highway engineer can be involved in projects that use all or some of the techniques listed below: * surveying, * mapping, * gaging, * excavating, * grading, * filling, * backfilling, * tiling, * paving, * sweeping, * marking, * lighting, * monitoring, * controlling, * adjusting, * repairing, * maintaining.
They also need to be aware of environmental factors such as soil type, moisture content, frost depth, wind speed, etc. that may affect the selection of surfacing materials. Designing road surfaces that take these factors into account will help ensure the safety and durability of the road for future users.
Finally, highway engineers must determine the optimal mix of usage levels for the network, including recommended speeds, traffic volumes, spacing between lanes, etc. This involves taking traffic data on existing roads and predicting what will happen if other routes are built. It may also involve making temporary changes to the configuration of roads during major events like sports games or parades.
The road's orientation is influenced by class and function. National and state highways between two stations must be kept as straight as feasible, although other types of roads may be permitted to deviate when required. The term "as straight as possible" means that the highway department responsible for the road should attempt to locate their center line along the median or center strip of the road if one is present. If this cannot be done, then they should be located as far from the edge of the road as possible.
The direction in which traffic moves on a road is called its alignment. This is usually indicated by physical features on the road such as ditches on one side and a center line dividing the road into two lanes. Traffic flows toward the ditch on the outside of any curve or bend in the road. These are known as outside curves.
Inside curves are used to connect one section of road to another. They can be seen on most roads with three or more lanes. Here, the middle lane is split by a white line (or some other indicator) so that drivers know where it is safe to go around the curve. The outer lane is where you want to be if you're trying to make it through a curve safely.
Roads are usually built with horizontal layers separated by vertical barriers. The horizontal layers include dirt, gravel, sand, and concrete.