HOUSTON — On the muggy streets of suburban Houston, amid McMansions, bright green lawns and stately oak trees, a futuristic race is quietly afoot.

The contestants are not people but late-model Toyota Priuses outfitted with an array of sophisticated sensors. Despite fierce competition and unending pressure to perform, the nearly silent electric vehicles do not speed. They move cautiously, rigorously following traffic laws and never topping 25 mph.

Their goal is not an easily discerned finish line but to map large swaths of the nation’s fourth-largest metropolis, a sprawling patchwork of neighborhoods, mini-cities, strip malls, gridlocked superhighways and mazelike gated communities — an area so prodigious in size it easily could swallow Manhattan, Brooklyn, Queens and Staten Island whole.

The vehicles are owned by Nuro, a Silicon Valley robotics company with an ambitious goal — to become the world’s preeminent autonomous delivery service, allowing millions of people to have groceries and other goods delivered by robots instead of making trips to the store, potentially reducing traffic and kicking off a new chapter in our relationship with machines. For months now, Nuro’s robotically piloted vehicles have been successfully, if quietly, delivering groceries to restaurants and homes around Houston, the vehicles’ sensors mapping the city as they go.

The faster Nuro’s vehicles map Houston’s notoriously chaotic roadways, the faster the company can refine its software and export its business model elsewhere. But time is in short supply.

Like Nuro, companies such as Amazon, Alphabet-owned Waymo, Robomart, General Motors’ Cruise division, Ford-affiliated Argo AI, Starship Technologies and many others are also rushing to deploy high-functioning autonomous vehicles for delivery and passenger transport, with some companies attracting major deals and billions in funding. Their goal is to earn public trust and offer real-life convenience, experts say, heightening their chances of securing a valuable foothold in a new era defined by autonomous transportation.

To get there, they will first have to run their autonomous vehicles, or AVs, through millions of miles of driving tests in cities such as Houston until they are glitch-free and unquestionably safe.

“The pressure is real,” said David Syverud, head of robot operations at Nuro. “And to be clear, it is a race in the AV space to deploy quickly and be the first to really get there.”

As with any race, more speed engenders greater risk, particularly in Houston, a car-dependent city dominated by construction, impatient drivers and the kind of busy roadways that present a serious challenge to experienced human drivers, much less robotic ones.

Each year, more than 600 people die on Houston-area roads, making the city one of the nation’s deadliest major metro areas for drivers, according to a comprehensive analysis of regional traffic fatalities, using 16 years of federal data, that was recently published by the Houston Chronicle.

Regardless of the risks, AV enthusiasts like Syverud are confident that there will come a day in the not-so-distant future when — almost no matter where your family resides — your groceries will be delivered to your home via an autonomous robot.

But to make that vision a reality, companies like Nuro have to build it from scratch, a herculean effort involving dozens of vehicle operators and hundreds of engineers working in synchronicity each day to test robotic systems and map entire cities.

After completing a successful pilot in the Phoenix area, Nuro, which has raised more than $1 billion in funding, arrived in Houston last year and launched autonomous deliveries for Kroger, the nation’s largest operator of traditional supermarkets, in April and began working with Domino’s Pizza in June.

The city’s reliance on cars has done little to burnish its national reputation, but it was a boon for Nuro. With an average commute of about 60 minutes round-trip, hungry Houstonians are eager to avoid driving any more than they have to, Nuro officials say.

Company officials say they were also drawn to Houston for the complexity of its metropolitan environment, a puzzle of independent communities, each with its own road conditions, zoning ordinances, parking rules and traffic laws. Some area neighborhoods offer wide lanes and little traffic, others are narrow and perpetually hectic — providing the company’s robotic software a massive variety of testing conditions.

As the country’s most ethnically diverse large city — and with a foreign-born population of 1.4 million — Houston also is a place where Nuro officials could probe fundamental questions about its business model.

“The big question for us is: Who is going to use this service, and how often will they do it?” said Sola Lawal, a Nuro product operations manager based in Houston who formerly worked for Uber. “Our robots don’t care who they’re delivering to, but we want to understand how different demographics interact with and feel about the robots. Houston allows for this broad swath of experience in one city.”

Delivering items locally to a customer’s door — particularly food that has to stay hot or cold — has long been one of the most expensive logistical problems in transportation, in part because of the labor costs. It is far cheaper to transport hundreds of packages in the back of a UPS truck with multiple drop-offs at addresses along a set route. That has helped hinder the online spread of grocery delivery, which can be cost-prohibitive when factoring in a driver’s wages.

Nuro appears to have found a way around that complication. Using the maps created by its current vehicles, Nuro plans to launch in the coming months a new version of its fully autonomous, passenger-less vehicle known as the R2. The company claims that a smaller delivery vehicle, such as the cooler-size delivery robots employed by Amazon or Starship Technologies, would be unable to travel at the speeds and distances necessary to make autonomous grocery delivery efficient in Houston.

A larger vehicle without a human driver offers other benefits as well, according to Nuro — more space for groceries, better maneuverability and braking, and no need for interior safety features to accommodate people.

Regardless of what robot does the job, for Yael Cosset, the chief digital officer for Kroger, a partner to Nuro’s test in Houston, there is little choice but to embrace autonomous delivery.

“A few years ago, we were telling customers that if they place an order today we can have it ready for them tomorrow afternoon, and that was okay with them,” Cosset said. “Today, some of our customers will expect that same order to be available within the hour.

“Now, if you need a roasted chicken and pizza and a bottle of milk in the next 45 minutes, I can fulfill that demand for the customer because of Nuro, which is a critical component of our delivery modalities,” he added.

When a robotically driven vehicle pulls up to a home with groceries, two Nuro employees — known as vehicle operators — are always inside. (That will change when Nuro launches its fully autonomous R2 vehicle in Houston later this year.)

Each day in Houston, all 65 of Nuro’s vehicle operators, working in teams that consist of a driver and a co-driver, are tasked with preparing Nuro’s fleet for the road. Already, the company says, drivers are making dozens of deliveries a day, many of them, somewhat surprisingly, to businesses in Houston’s bustling restaurant scene.

Like driving instructors overseeing an artificially intelligent teenager behind the wheel, operators — who remain ready to wrest control of the car from the robot if something goes wrong — monitor and document turns, braking and acceleration as the vehicles, outfitted with dozens of navigational sensors, quietly roll from one street to the next, creating a hyper-detailed map of the city.

Though their job may sound uneventful, vehicle operators say they must remain in a state of near-constant focus for hours at a time — punctuated by brief moments of extreme intensity. As the vehicle moves, the co-driver, who has a laptop that monitors the robotic system, verbally informs the driver of the robot’s intentions before they occur — a cue known as a “call-out.” The driver’s job is to listen to the call-outs and ensure the vehicle is behaving appropriately while monitoring the driving conditions outside the car.

There is no eating in the car, and drinks must be sealed. To keep things fresh, drivers and co-drivers switch places every few hours and take periodic breaks.

Narrow streets, potholes, construction and low-hanging tree branches are obstacles that offer the team a chance to improve the vehicles’ neural network, in hopes of bringing full autonomy to life. But the biggest obstacle is a human one — an aggressive driver in another vehicle, frustrated by the robot’s slow-moving, law-abiding style.

“What keeps me up at night is a member of my team being injured by a human driver who is drunk or distracted,” Syverud said.

Many of the company’s vehicle operators, such as Troy Veuleman, have no background in tech and found their roles through online job postings. Working as an emergency medical technician in Shreveport, La., for four years, Veuleman grew accustomed to long, stress-filled hours behind the wheel of an ambulance, often with little downtime between shifts.

Whether he was racing through rush-hour traffic with a patient in critical condition aboard or keeping a gunshot victim calm when the person’s life depended on it, Veuleman said he honed the art of remaining clearheaded and decisive amid a daily stream of heart-pounding drama.

When he decided to switch careers last year, those same skills — as well as an exceptionally clean driving record — made the 25-year-old an attractive candidate for sitting behind the wheel of a robotically driven car and remaining alert for hours on end.

To prepare vehicle operators to endure the tedium of the roadway, Syverud said he reminds his employees that they are part of a larger mission, using a message that Chris Urmson — one of the architects of Google’s self-driving-car program — used to tell his staff: About 40,000 people die on the roads every year, which is roughly the equivalent of four Boeing 737 Maxes falling out of the sky every week.

Nuro’s staffers, Syverud said, have an opportunity to lower those numbers by keeping people off the roads.

For employees like Veuleman, that urgent message resonates like a call to duty. During long days inside the car, when it is tempting to take one’s eyes off the road, the former EMT tells himself that though he is no longer saving lives in the present, he may be saving them in the future.

“I come from a world where you’re literally helping people and saving lives each day,” Veuleman said. “This role is different. But there is definitely a mission in place, and we believe that making the roads safer can actually change the world.”