The convention in the USA for old urban centers and new suburban sprawl is to construct a street or road with a crown that drains rainwater to gutters along both sides of the road, then have storm drains to convey the water from the gutter to some nearby creek or tributary. But why?
Wouldn’t it be easier to construct the road in a roughly canal shape, so that rainwater drains towards a single V-shaped gutter at the road’s center? This would cut the number of storm drains by roughly half, prevent leaves from falling directly into a drain and clogging it, make it possible to clear a drain by driving a streetsweeper over it, and also prevent a clog from flooding adjacent properties, since the road itself can temporarily impound more water until municipal authorities can clear the blockage (whereas side gutters would invariably flood the sidewalk and carry sharp debris that would damage tires entering a driveway).
Furthermore, a center drain can be built once and then retained as-is each time a suburban arterial needs expanding – “just one more lane, bro” – whereas side gutters are regularly demolished and rebuilt to accommodate additional lanes. By routing water away from the edges of the road, sidewalks avoid freeze/thaw cycles, and the road surfacing can be continuous from the curb: no more bike lanes in the gutter. As a convenient benefit, the “drop” off at a curb-cut from a driveway to street level would cease to exist.
And where required to improve water quality due to runoff pollution, a center drain can be excavated and rebuilt as a linear stormwater retention pond, where moderate stormwater can filter into the local soil slowly, with a predefined overflow level that will drain to the existing stormdrain pipes. This is already done for both surface parking lots as well as Interstate highways, so it’s not an unproven design.
Narrow alleyways in older cities do use a central drain, so I can’t see why the idea stops making sense for larger streets and roads. The only drawbacks I can envision are aesthetic – a neighbor’s excessive lawn irrigation would draw a wet line across half the street – and that the center channel would also carry leaves and wayward soccer balls into the middle.
But even still, that doesn’t seem worse than the status quo: gutters attract all sorts of detritus, but it’s usually hidden beneath the wheels of parked cars until something punctures a tire. And at least in water-starved California, irrigation runoff deserves to be noticed and called out so that it gets fixed. There may even be some small road safety benefit from having a V-shape channel in the center, since it would unmistakably divide opposite sides of the street.
For larger arterial roads that have trees in the center, this seems like free irrigation and water pollution control. It even works when the center traffic lanes are converted for running a tram or light rail train.
What am I missing here?
During heavy rainfall, intersections would become lakes in the center, where most traffic is going straight, at higher speed than turning, and nearest to opposing traffic.
The drainage needs to go into something hollow, having a hollow space beneath the part of the road that needs to support the most weight of vehicles means needing to create more load bearing hollow spaces than would otherwise be necessary.
I would question why road traffic is driving very fast in “heavy rainfall”, but the solution is the same: truncate the center gutter before the intersection, so that the intersection itself drains conventionally, into the center gutters on all approaches to the intersection. Alternatively, where it makes sense, use a center drained roundabout.
having a hollow space beneath the part of the road that needs to support the most weight of vehicles
My understanding is that there is only one storm drain pipe underneath a street, somewhere near the center, and each side of the road has laterals that connect to this pipe. There are not two pipes, one for each side of the street directly under the edges of the paved surface. If it were literally under the curb, service manholes would be impossible. See https://www.amwua.org/blog/only-rain-should-go-down-the-storm-drain (relevant image only shows up on desktop mode)
Storm drains, aqueducts, and swimming pools are typically made out of concrete because it has the right properties to deal with lots of water. Roads are typically paved with asphalt. Unlike concrete, asphalt is far more subject to damage from water.
One of the main purposes of crowned roads is to ensure that water flows off the asphalt quickly in thin sheets that don’t cause erosion. A heavy flow of water on asphalt causes too much erosion. Also, pooling or standing water seeps into asphalt and causes damage and structural problems. Especially in areas where the temperature gets low enough to freeze.
There are also other problems with V shaped roads, but avoiding water damage from pooling and erosion is the big one.
Slightly V shaped roads are used where cars don’t go, like in pedestrian shopping centers with outside walkways.
Just my educated guesses as a layman, but I agree with what others are saying in that a center channel would lead to more flooding in the streets. Side drains won’t flood streets or homes (unless its an actual flood) as both are elevated above said drains. Side drains also give 2x the holding capacity which further helps reduce water pooling on the road.
Additionally, having it in the center of the road means any maintenance done on said drains is going to block both lanes of travel, and even if it doesnt, would put workers in a very dangerous working position.
First, if the road floods, that would push drain clogging debris into the road, not away from it, and while many roads can operate a slight clog at the side, it becomes more problematic at the center.
Secondly, if it does clog, regardless if it was from a flood or just litter flowing into it with normal rain, some one has to go unclog it.
That someone would then either have to shut down both directions or be at risk of being hit from both directions.
Third, with the way roads are constructed, it would be a lot more expensive to design the sewers to either tolerate the loads (imagine a big heavy truck,) or burry it deep enough that the load is distributed around it anyways.
Fourth, maintenance. If something happens where you need to dig up your sewer, putting it to the side means you’re not also digging up the road. The reverse is also true.
Fifth, in freezing conditions, you don’t really want the water pooling in the center… you want it to the side, at least before it freeze back into ice.
it becomes more problematic at the center.
This is precisely what I’m trying to understand: what gets more problematic? The driving? The civil engineering? What is the exact complexity that a center drain would introduce?
some one has to go unclog it.
Conventional drains along the curb also need to be unclogged manually, except that the public works dept needs to get people to move their parked cars, which can also hide the problem from being easily noticed in the first place.
either have to shut down both directions or be at risk of being hit from both directions.
From seeing how my town accesses manholes located in the middle of a two-way road, they arrange two heavy trucks in a row, one before and one after the manhole. On a multilane arterial, this is a minor traffic disruption of one lane. On a quiet residential street, people just go around slowly.
with the way roads are constructed, it would be a lot more expensive to design the sewers to either tolerate the loads (imagine a big heavy truck,)
I believe that roads are infact designed with the sewer and storm drain pipes directly below the traffic lanes. See my other comment. A cursory review of my town’s planning documents for a new road extension shows a cross section that has all longitudinal piping underneath the lanes, so that the manholes aren’t installed under sidewalks or the curb. I am open to seeing plans for other jurisdictions that build their pipes differently.
