Railroad Surveys
Railroad surveys are conducted either during the initial design and construction process or to aid in ongoing maintenance projects. Surveyors assist engineers in the mapping of optimal rail routes, and also determine optimal grades, slopes, and curves in varying sections of the rail route.
The railroad survey is an essential step before any drawings can be made of potential railway routes. It is necessary to understand the geographic restrictions and the layout of the area before attempting to determine the best route. In an ideal world, the rail line would run in a perfectly straight line from start to finish, with no changes in slope and no turns, since this would be the shortest distance. If this were possible, a surveyor may not be necessary. However, in the real world there are geographic obstacles that nearly always make this impossible.
As the surveyor determines the optimum rail route, there are a few restrictions to keep in mind. First, the rail line should climb no more than two meters in altitude for every 100 meters traveled. When it comes to curve, gentle curves (under 10 degrees) are optimum, though tighter curves may be possible or even necessary in some areas. One major difference between highway surveying and railway surveying is in how angles are measured. On highways, curves are defined using the ARC method, while railway surveyors use the Chord Method. This method allows for easier determination of curves in the field. When determining optimum route, the surveyor also takes into account the track gauge (how far apart one rail is from the other), and regulations such as maximum train length, if any exist.
During this step of the railroad design process, the surveyor is mostly concerned about the track, since no other design elements will be relevant if the track is unusable. Other than providing location input, the surveyor may also create a 2D or 3D representation of the site. Often this takes form as a cross section, allowing viewers to see how the railway will look from the site itself. In other cases, the surveyor’s work takes the form of a 3D computer generated image showing the line’s ideal location when current geography is considered. This image may be manipulated to allow viewing from any side or angle.
Perhaps the most challenging part of rail road surveying is the necessity of bridges and tunnels. The surveyor may be responsible for providing input on site selection and monitoring the building process to ensure that the bridge or tunnel is located correctly. The surveyor’s job is made more difficult when tunnels are involved rather than bridges, as the tunnel must be bored completely straight through the hill or mountain.
Once blueprints for the rail line have been created, the surveyor again plays an important role at the railway site, in determining that the construction crew has accurately located the rail line on the physical land when given the blueprint. From laying the track perfectly level and in the proper location to following a blueprint to determine where the platforms and stations should be placed, a surveyor is involved in every step of the way. The surveyor’s job continues to signal poles, electrical wiring, drainage, and other aspects of the railroad project. Various laser devices are often used to gain an accurate depiction of the railway area. In some cases, these lasers can also evaluate the integrity of the track material itself, a valuable tool for maintenance crews.