Folks at the Public Works Department are quick to note that Houston roads actually are not that bad. Every day they bear thousands of miles worth of traffic jams and hold up alright. The city gets by comfortably.

But maybe a few of the roads have more bumps, cracks, basins, dips, fissures and potholes than Houstonians would prefer. It's a running joke here. But it's not without reason.

According to Carol Haddock, deputy director of Houston's engineering and construction division, "Water is the enemy of the roadway."

And Houston gets a lot of water. Then sometimes it doesn't. So the climate feeds the cyclical wetting and drying this region's so-called "expansive soils"—the clay sediment that makes up the ground beneath Houston.

With water it swells like a soaked sponge; without it, the soil cracks and crumbles. Early Houstonians were keenly aware of expansive clay soil. Back then they called it mud.

EXPLAINED: The trouble with living in a swamp

Consider the account of Ferdinand Roemer, who explored Texas in the 1840s.

"Hardly had we left the city when the flat Houston prairie loomed up as an endless swamp. Large puddles of water followed one another and at several places a large section of land was under water," he wrote. "The wagons sank deeply into the mud, compelling the horses to pull them slowly, step by step. Often the wagons became so mired that it required the help of our members of our company to push them out of the bog."

How about you try paving over a swamp and see how long your roadway lasts.

The young city tried covering mud roads with cypress wood planks, but they floated away in floods; they tried laying stone blocks, but the wagon wheels pushed them deep into the soft mud.

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It was a drainage system that ushered the water off the roads and made pavement possible.

But in the year 2016, that same sometimes-swampy soil still exists beneath that same rainy sky. Now it's just covered with concrete.

That concrete rests on the earth beneath it. So when that earth moves, either expanding or contracting, the concrete loses its support and breaks. This effect becomes most pronounced with dramatic swings in weather.

EXPLAINED: How record rains yield to record drought

For example, between 2011 and 2015 Texas endured its second worst drought on record. In Houston, the earth beneath our roads contracted. Home foundations cracked across the city. Water mains broke. Haddock said some parts of town went from one to two potholes a year to 10 to 12.

RELATED: Drought causing cracks in more than just soil

Then 2015 became the state's wettest year on record. Every time the pavement soaks under standing water it gets a little weaker. And the soil again reforms under the weight of the road.

RELATED: Floods in 2015 do billions of dollars of damage to Texas roads

"It speeds up the process of our roads degrading," Haddock said.

To make it worse: The engineers who built most of Houston's roads in the mid-20th century couldn't have foreseen the growth in population and vehicle traffic that the new millennia would bring.

Once that degradation process passes a threshold, the road must be replaced or drastically renovated. Our city streets aren't quite the Roman roads and aqueducts that stand two millennia later.

According to a study on transportation infrastructure from the Georgia Institute of Technology: "Transportation infrastructures have different design lives, that is, they are expected to last under normal loads for a specific number of years. Pavements, for example, depending on the type of materials, vehicle loads, and environmental factors can last anywhere from 10 to 20 years before being replaced."

Haddock said the city recently updated criteria for roadways; now they're built to last 50 years.

But if you divide the city's miles of roadway by the funds available each year to fix and replace them, a problem emerges.

"We don't have enough money to get back to that road in 50 years," Haddock said. "It would be about 200 years."

EXPLAINED: Why your street won't be fixed anytime soon

The projects are more expensive than they seem: when the city rips up a road, they take the opportunity to rebuild the drainage system beneath it. And scheduling is complicated: the streets must remain passable when while construction rages.

Where a total street rebuild isn't possible, the city does what it can: overlaying asphalt or cutting out bad chunks of road and replacing them with concrete planks.

Under the Rebuild Houston program, the city has completed hundreds of such projects since 2012. It's a small chunk out of a big problem, and every year more old roads join the backlog of projects.

But there is hope. Much of the ReBuild funds are currently used to pay off old debts. As those debts taper off in coming years, officials say the ReBuild budget will double.

"We will freely admit that we have a big chore ahead of us. We have historically invested in rebuilding our roads about 25 to 30 percent of what we believe we should be investing," Haddock said. "We're seeing being able to double the amount of work we do in five to eight years."