| Elements of Railroad Surveying | | | | Rail Track Geometry |
| As with most building projects, surveying processes | | | | The railroad surveyor is mostly concerned about the |
| prove useful in two distinct aspects of rail design-initial | | | | track. While there are certainly other issues to |
| construction and ongoing maintenance. Surveyors are | | | | consider-width and height of the road bed, right-of-way |
| employed to map out optimal rail routes and also work | | | | clearance above and on either side of the bed, and |
| closely with engineers to determine what sort of | | | | the proper placement of poles, mile markers and |
| grade, slope and curve to put where. A site survey is | | | | such-the transportation system will not operate |
| necessary before any drawings can be made, since | | | | properly if the rail itself is out of place. A number of |
| one must understand the geographic restrictions at | | | | devices are available to make sure that the geometry |
| hand before hoping to surmount them. Once blueprints | | | | of the track stays true. High-speed scanning is one of |
| have been created the surveyor is again engaged, this | | | | the more recent innovations in this area. Employing |
| time to ensure that the construction crew is accurately | | | | laser imagery and customized software, the railroad |
| reproducing the design created by the engineering | | | | surveyor can enjoy the scanning density of nearly half |
| staff. Every element involved in a rail project requires | | | | a million points per second. This process identifies the |
| the attention of a surveyor, from laying the track level | | | | integrity of the rail material as well as its proper |
| and in the right place to proper location of platforms | | | | placement on the rail bed. The imagery created during |
| and stations, plus other infrastructure items such as | | | | the scanning process can be generated in 2D |
| signal poles, electrical wiring and drainage. | | | | cross-sectional form. When combined with photo |
| Rail Line Complexities | | | | imagery, it can give surveyors and maintenance crews |
| In an ideal setting, a rail line would run straight and true | | | | alike an accurate 3D picture of the rail's condition. |
| from start to finish, with no changes in grade. In that | | | | Bridges and Tunnels |
| case, you would hardly need a surveyor at all. Since | | | | Perhaps the most challenging aspect of railway design |
| few circumstances permit this, though, there are | | | | involves the construction of bridges and tunnels along |
| certain parameters a railway surveyor must follow | | | | the right of way. Various aspects of engineering come |
| when laying out a rail route. First, any grade (climb in | | | | into play when creating an optimal design for each. For |
| altitude) should be no steeper than two units high for | | | | bridges, the railway surveyor provides input on site |
| every 100 units traveled. In other words, a train bed | | | | selection as it concerns the geometry of the approach |
| should climb no more than two meters in elevation for | | | | (cuts and embankments) and the track alignment along |
| every 100 meters of track. When it comes to curves, | | | | the bridge floor. During the construction phase, the |
| anything more than 10 degrees is probably a bad idea, | | | | surveyor is responsible to monitor continuously all |
| although you might be able to get away with a tighter | | | | aspects of the build-out. For tunnels, the railway |
| turn if the curve is more steeply banked. Naturally, | | | | surveyor's pre-construction input is similar to that for |
| many of these measurements will depend upon | | | | bridges. During the digging phase, however, his |
| factors the surveyor should know in advance. These | | | | participation is even more critical due to the necessity |
| would include such things as the track gauge (how far | | | | of locating the centerline above the site and then |
| apart the rails sit from each other) and the maximum | | | | translating it to a viable straight-line bore through the |
| number of cars allowed (if such a restriction exists). | | | | rock while avoiding drift. |