Submitted by koobtooboob t3_10oy3vt in explainlikeimfive
Isn’t it more work/danger for engineers and drivers to make the roads curvy? Land will be terraformed eventually so the only reason I see for irregularly shaped roads are to avoid things like mountains or bodies of water. The only benefit I can think of for non-straight roads is that it might force drivers to be more alert but I somehow doubt engineers were thinking of that.. or were they?
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The roads came before cars here and were probably started as walked trails at some point so it wouldn't have been necessary for them to have been straight and flat.
But in a place where the roads were designed post car invention I reckon its a mix of how the ground underneath I and how the topology of the land is, avoiding sandy or shale patches and areas that might flood is probably a priority to prolong the life of the road surface itself.
Like most things, it usually comes down to money. It costs far more money to have a road go through the center of a hill than it does to go over or around it. It's cheaper and easier to build a bridge at a narrow section of a river with solid bedrock on both banks than it does at a wider section with sandy banks that will need to be reinforced.
Another major factor is existing property roads and lines. Many years ago, "roads" were often just cart tracks or horse trails, upon which people just rode through the most-convenient terrain (avoiding muddy areas, thickets, craggy rocks, etc.). When those areas became more settled, property lines were often drawn based upon where the existing paths/roads were. Thus, if you tried to straighten out the roads, you would have to keep separating parcels of land and demolishing homes.
And, of course, climate must also be considered. You don't want to build a road right through an area that is prone to flooding or avalanches or wildfires, just to keep the road straight.
There are a lot of places where it is dificult to build roads. Such as hills, mountains, lakes, rivers, oceans, wetlands, etc. In addition to this roads tends to be built where people live. It is more efficient to build roads between the towns in an area then to build it straight and build lots of smaller roads connecting the towns to the main road. So if you look at a map you will see that the roads tends to go in straight lines connecting all the towns, mountain passes, bridge sites, etc. together. But that means a lot of turns as there are lots of these along the route.
Because things get in the way.
Mountains, rivers, hills, buildings, ravines, forests and more are just some of the things that get in the way of roads just being straight. Most of the time, it's much cheaper to build around something instead of going straight through it. Other times, you have no choice but to curve around it; it doesn't matter how much you'd like to make the road straight, you're not going to get permission to tunnel through Notre Dame cathedral.
Bridges are orders of magnitude more expensive to build than regular roads, so if you can avoid building a bridge over something, you will. Tunnels are even more expensive to build. Both tunnels and bridges are more prone to collapse in the event of natural disasters, and both of them introduce areas of natural bottleneck in traffic flow; if it turns out that you didn't make the tunnel wide enough for the amount of traffic you need to accommodate, it's much more expensive to widen the tunnel later on, and you'll likely have to shut down the tunnel while you're widening it.
Long stretches of straight road cause more accidents as they can be boring/cause drivers (esp long haul truck drivers and similar occupations) to fall asleep.
Also, many drivers drive faster in long stretches of open road.
This is why they (engineers/traffic or city planners) intentionally put even sight curves into long straight roads/tunnels etc even when it's possible to just make it straight.
Source:
https://ssti.us/2019/10/28/more-sharp-curves-make-roads-safer/
Road are straight where possible, however they tend to go around obstacles like hills and mountains and swamps and rivers.
They also have to actually go where people want to go. They need to connect town and cities that people travel between and unless those were built in the very recent past, they are not on a straight line.
In some parts of the world current roads can follow roads that were laid down centuries or millennia ago.
Those roads were also built as straight as possible because people 2000 years ago also anted to get to their destination as fast as possible, but technology has changed since then quite a bit.
Roads always try to be as efficient as possible, but the balance of what is most efficient changes over the generations as building bridges and tunnels and moving large amounts of earth around gets easier and people travel faster on roads.
If engineers could build roads completely straight they would, the landscape just gets in the way.
Engineers want you to pay attention to the road, the most useful trick they have, is follow the terrain topography. Unfortunately, the topography doesn't always work with you, because the straighter the road is the more boring and fatiguing it becomes, so much so, Australia has fatigue zones in some highways where to keep you awake and alert, there's trivia questions every few miles.
Alsoto note:even straight roads are not straight. The are slightly curvy and build with at least 2° angle for the sake of removal of water and dirt.
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Grade/terrain. Depending on laws usually 4% is max safe grade otherwise dangerous in winter etc. roads are needed to zigzag up slopes. Erosion is also an issue
Also, more basically, the globe is a sphere. It's impossible to have all straight lights in a ball. They would be unnecessarily close at one part and unreasonably far at another part.
Allow me to add to this:
It's incline and human laziness. Earth isn't flat but has stuff on (and under it), that is also a reason why we dont have vertical roads (even if we can build them).
In engineering, there is this thing called rise (basically a tangent) it's used to figure out distribution of force across some incline. So in the same way that climbing a 10 m of ladder is harder than walking 10 meters straight, getting up 5 meters in height over 10 m, asks for more energy to compensate for force distribution.
We peeps are very, very lazy. I mean I could go to the village and get cheap and organic produce, but that commerce store is right next to my door. So in the same way we dont like to use roads or go places that are more difficult than walking straight (and it isn't safe for trucks and other vehicles with low centre of mass). So if you need an incline of 5% for any pass to feel easy, that means that for an elevation of 1m, you need a ramp of 20 m. Now that is the bummer about inclines, because to get to 1000 m elevation you need to have road so long, that no neighbouring city can use it (ie 20000 m) - so we tend to pack it into twisty and turny shapes because if we dont there is no point to it.
So engineers tend to design stuff in such way that if you gonna use it, it will be easy... and even if you feel like a daredevil, chances are low enough that you will hurt yourself. That brings the research mentioned above into the topic.
See, we are lazy but also easily bored (listen I never said humanity was easy or simple). To put it in eli5 terms ... more nothing changes, more your internal race car driver wants to take a wheel. So even if we make it so that, if one wants to go daredevil, they are 90% safe... more time they have on such road more daredevilly they will become and more they go into that 10%.
In actuality, falling asleep has no correlation with road length, but rather increase of speed does. So we tend to make visual, auditory and inner ear stimuli at around 30 min marks at every road (due to this). This is why roads have speed limits, and why they are measured in hours. If you are going 60 mph at 30 miles you will have some tree, some sign or something that resets your inner daredevil.
So to climb up/down - we need long roads, to make them fit we make them sort them like straws. Length of a straw depends on amount of time where people need a stimuli refresher.
If anyone has inner ear problems during non straight roads.... it's not the roads it's the driver. You can always drive 30 in 20 zone, but those stimuli are passing 1.5 times faster. To some their passivd attention has no effect to their inner balance - ie they don't register set stimuli. For others, it does so their brain gets lots of inputs. It's like trying to listen to audio book while watching unrelated movie and tooning in on your neighbours fight - while you can't get away because it's a moving vieachle.
Don't forget the nimbys. Places where a well to do land owner is so connected they say nah... put it somewhere else. Look for hard right turns in rural area highways. Also interest groups and neighborhood coalitions these days. Look at all the stink around I45 downtown Houston. Also keep in mind that turning a car 90 degrees at 70 miles per hour takes a lot of curved roadway. Think about how long the interchange ramps are around Beltway8 Houston.
sandiercy t1_j6heh6o wrote
Where I live, we have a bunch of straight roads, we also have areas where it is literally impossible to build roads so we have to go around (things like mountains or bogs). Coastlines also make it nearly impossible to have a straight road.