Why do most roads have a lot of bends? What is the process a civil engineer takes in planning out roads depending on their terrain? Is it hard to make more straight roads in canyon/mountain areas and why?
In: 3
Great question. The alignment of a road is determined by a number of factors. If you consider cost as a primary factor, the reasons become more obvious.
A straight line, is the shortest path but not the most economical for the construction cost.
Let’s take a simple case a hill, you could make a line straight through it but it would require the excavation of the hill removing the material and getting rid of it. However the cost of going around would cost less to construction.
Roads are built in such a way as to minimize the amount of material that you must excavate and also fill in. This is called balancing cut and fill. You design the road’s vertical alignment cost is minimized by doing this.
The horizontal alignment cost is minimized by avoiding bodies of water, significant hills and so forth.
The actual process is done by taking all of the data about the horizontal and vertical topography (layout of the earth.) Then a series of alignments are computed until the alignment that minimizes cost while meeting other design criteria is selected.
How hard it is to make straight roads is not the major concern, the relevant factor is the cost of doing that. That is hard as in if we can do it.
A straight road will be one that does not curve in the horizontal and the vertical. If the ground is not flat, to begin with, that requires the moment of a large amount of material and that costs a lot of money. The result is that less work is required if following a path where the round has close to even elevation or change slowly if the elevation of one end is different from the other. The result i that you get lots of curves.
If you look at road construction how straight do you like them to be depend on when it is built and the amount of traffic.
Today we build them straighter than in the past. In part, because the machines that can move stuff are more efficient. Another reason is traffic has increased and how safe we like the road to be. Staiger roads are safer and the effect is large if there is more traffic.
There is also a difference in expiration, a straighter road can have a higher speed limit.
So how road is built are a compromise between construction cost versus road speed, road capacity, and safety.
When you design a road, you are trying to minimize the amount of earth that you have to move, because that’s the cheapest way to build the road.
A road has a design speed, and that design speed dictates how comfortable the driver will be. The radius of curves, and how much room you need when you transition from an uphill section to a downhill section, are both governed by the speed. Drivers can tolerate much tighter curves when driving slowly, because there’s less lateral G-force.
So at a first cut, you plan your road in the straightest line from Point A to Point B. If that’s going to require blasting the top off of one hill, and filling in a deep valley somewhere else, you’re probably going to modify the route so that it more closely follows the existing terrain.
Latest Answers