Railroads, in many instances can provide a more efficient way of transportation. For example, in developed countries like Europe or Japan, people can access to almost anywhere, including to or close to even small towns, with railroads and the big cities have extensive metro networks, which are also considered as railroads, from civil engineering point of view. The benefits of railroad vs car transportation are virtually limitless, in terms of economy, environment, speed, efficient use of land and more.
The geometric design concept of railroads, in terms of horizontal and vertical alignment is in principle similar in to road design, with necessary differences and lower tolerances. For example, the cross section is obviously different, and in general railroads curves, grades and superelevation slopes must be less and clearances, and curve transition lengths more than roads. Railroad cars and locomotives are heavy and they impose more loads on the foundations. Not only that but also the vibration must be prevented, which is harder to do especially with faster moving trains. Therefore the foundations of railroads also have stricter requirements. Similarly, bridges that will support railroads, must be made for heavier loads, and smaller movement tolerances than the bridges that will support car and truck traffic. Even for bridges that will support passenger trains, which are shorter, faster and lighter than freight trains, this requirement holds true.
Similar to road subgrades, railroad subgrades must also be made from granular materials by compacting them. We will cover more on this topic later.
In the next post, we will talk about considerations that come into play when designing railroads.