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 the lowest part at the center of the road? 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?