After years of unmet promises, hydrogen vehicles could finally be catching on. If so, it'll be a convoy of clean semi-trucks — not a bunch of quirky passenger cars — leading the way.

The big picture: We've been hearing about zero-emission, fuel-cell vehicles for decades as the answer to our worries about fossil fuels and climate change. But even now, the economic and practical challenges are still too difficult to overcome — except, perhaps, for commercial truck fleets.

The state of play: Like carmakers, truck manufacturers are under intense regulatory pressure to cut carbon emissions.

• Tesla is developing an electric semi-truck, but most manufacturers say electric trucks make sense only for shorter routes.
• Strapping a bulky battery under a long-haul truck is impractical if it takes up space that could otherwise be used for revenue-producing cargo.

Driving the news: Several heavy-duty truck manufacturers this week announced they're rolling out hydrogen-powered big rigs.

• Hyundai delivered its first fuel cell trucks to customers in Europe, and said it will start selling them in the U.S. and China next year.
• Toyota and its Hino subsidiary said their first fuel cell truck will arrive in North America in the first half of 2021.
• Hyzon Motors, with help from an investment announced today by French energy giant Total, expects to deliver about 5,000 fuel cell trucks and buses over the next three years.
• General Motors is negotiating a partnership with Nikola, a hydrogen truck startup in Arizona.

How it works: Unlike conventional gasoline or diesel cars or trucks, fuel cell vehicles combine hydrogen and oxygen to power an electric motor. The only tailpipe emission is water vapor.

• One advantage of hydrogen fuel cells over battery electric vehicles is that they can be refueled in less than 10 minutes, vs. 30 minutes to multiple hours for EVs, depending on the power source.

Between the lines: A number of automakers, including Toyota, Honda, Hyundai and General Motors, have tried to market hydrogen fuel-cell cars over the years with little success.

• They sold only 7,500 worldwide last year, including just 2,089 in the U.S.

The biggest stumbling block to acceptance (aside from the cost of the technology) is finding a place to fill up.

• There are about 115,000 gas stations in America today.
• Yet there are just 42 public hydrogen stations, all but one of them in California.

Commercial trucks, on the other hand, don't require a large network of hydrogen fueling stations, especially if they're operating on set routes. An entire truck fleet can be refueled at a designated terminal.

• Long-haul operators could build a series of hydrogen fueling depots, 400 or 500 miles apart, along heavily traveled routes.
• Companies like Nikola even hope to produce hydrogen from renewable sources on-site at its fueling stations.

What to watch: Hyundai officials tell Axios they haven't given up on fuel cell passenger cars, and that the hydrogen ecosystem they're developing for trucks will eventually bring down costs and make hydrogen-powered cars feasible, too.

• The catch: Battery technology, meanwhile, is leaping ahead, making electric cars cheaper and more appealing to consumers.
• Yes, but: Rapidly increasing demand could pinch battery supply chains in a few years, warns mobility analyst Sam Abuelsamid of Guidehouse Insights.

The bottom line, says Abuelsamid: "I don't think we necessarily have a single solution. We could absolutely have both hydrogen and battery electric vehicles."

If you want to ride in a driverless taxi, your opportunity has finally arrived.

What's happening: After two years of tightly controlled operation in Chandler, Arizona, Waymo is opening up its driverless taxi service to the public.

• Service had been suspended back in March because of the coronavirus.

Why it matters: This is a big deal — a real driverless taxi service, with no one in the driver's seat — that is open to anyone who downloads the Waymo One app.

The catch: You can only ride within a 50-mile radius of Chandler, a suburb southeast of Phoenix, and existing customers get first dibs.

• "We'll start with those who are already a part of Waymo One and, over the next several weeks, welcome more people directly into the service through our app," CEO John Krafcik wrote in a blog post Thursday.
• Rides in other parts of the city will restart in a few weeks, with human backup drivers and barriers separating them from passengers.
• That will allow Waymo to keep expanding its service area, Krafcik said.

One note about hygiene: Driverless taxis will be cleaned frequently by Waymo's service partner, AutoNation, and will be equipped with disinfectant wipes, hand sanitizer and an upgraded air-purification system, Krafcik said.

Say this about Rivian, the electric truck startup: it must have a lot of confidence in its product to enter the very first vehicle to roll off the assembly line into a grueling, 10-day off-road challenge.

Driving the news: Rivian's R1T pickup is also the first fully electric vehicle to compete in the Rebelle Rally, an all-female, off-road rally that kicked off yesterday.

• Competitors may use only a compass and a map — no smartphone or other GPS device — to navigate the 1,200-mile, secret route through the desert of California and Nevada.
• Points are awarded for navigational accuracy, not fastest time.
• Off-road enthusiast Emme Hall, an editor at CNET's Roadshow website, and teammate Rebecca Donaghe will pilot the Rivian.

The intrigue: If running an electric truck with 400 miles of driving range across 1,200 miles of desert sounds a bit problematic, consider this:

• The Rebelle Rally partnered with Utah-based Power Innovations to provide 175-kilowatt fast-charging stations along the rally route, and to power the Rebelle base camp, reports Roadshow.

Dispatch from Day One, via a Rivian spokeswoman:

• "First factory-built vehicle, though still a validation prototype. A little risky but fun too."

Go deeper: You can track the Rebelle Rally here.

Roadie, an Atlanta-based company that got its start using gig drivers to deliver lost baggage for Delta Air Lines, now figures to play a big role in delivering holiday purchases this year.

Why it matters: Demand for same-day shipping exploded during the pandemic, and is likely to increase even more during the holidays. Traditional parcel carriers have strained to keep up, often slapping surcharges on deliveries, leaving a lane for Roadie to help manage peak demand.

How it works: Roadie recruits drivers already on the road to transport goods en route to their destinations.

• Using an app, Roadie drivers can check for available delivery gigs before they head home from work, for example.
• A description of the item, the dimensions, address and delivery price are all presented ahead of time so the driver knows where they would need to go and how much they'd get paid.
• The driver takes photographs of the item at both pickup and delivery to ensure there's no damage.
• Retailers including Walmart, Tractor Supply and Home Depot (a Roadie investor) have tapped Roadie drivers to handle booming demand for fast deliveries.

By the numbers: Founded in 2014 by serial entrepreneur Marc Gorlin, Roadie has raised $62 million to date.

• The company claims more than 50,000 customers and a network of more than 150,000 verified delivery drivers across the U.S.

Virgin Hyperloop picks West Virginia to test high-speed transport system (Eric M. Johnson and Joey Roulette — Reuters)

• Why it matters: The $500 million public-private project will be a proving ground for Virgin Hyperloop and a place for U.S. officials to establish regulatory and safety standards for magnetic levitation technology that would whisk people and cargo through vacuum tubes at up to 600 miles per hour.

Pelosi says no stand-alone aid for airlines without bigger stimulus bill (Leslie Josephs and Jacob Pramuk — CNBC)

• Why it matters: Some 30,000 workers were let go last week, and airlines say without more federal aid, they will begin cutting service to some markets, making a recovery harder. But the chances for a deal before the Nov. 3 election are slim.

Bringing public transit back from the coronavirus pandemic (Jennifer A. Kingson — Axios)

• Threat level: Cities face an "existential" challenge to convince residents that it's safe to ride public transit, says Robert Puentes, president and CEO of the Eno Center for Transportation, a nonpartisan nonprofit.

This week I got out of the home office for two gorgeous days in Ann Arbor, Michigan, to evaluate 27 semi-finalists for 2021 North American Car and Truck of the Year.

Why it matters: I evaluate new vehicles all year long, but the annual comparison drive is the one time the 50 NACTOY jurors from the U.S., Canada and Mexico get to drive contenders back-to-back, on the same roads, under the same conditions.

The criteria: We look for vehicles that raise the bar when it comes to innovation, design, safety, performance, technology, driver satisfaction and value.

• We give awards in three categories — car, truck and utility vehicle.

The catch: The pandemic made everything harder this year.

• Auto factories were shut down for two months earlier this year, which means many vehicle launches are behind schedule. Just getting cars to evaluate in time for judging was a challenge.
• Social distancing is also difficult when journalists are cycling through vehicles one after another. Masks were required, and cars were disinfected between each driver.

The early line: I was impressed by the electric vehicles in this year's crop of nominees:

• The Ford Mustang Mach-E, a technology-packed crossover utility.
• The Polestar 2 sedan, from Volvo Cars' new performance brand.
• The Volvo XC40 Recharge compact SUV.
• All were innovative, responsive and exceedingly fun to drive, but they're all a bit pricey compared to gasoline vehicles.

What to watch: Thee finalists in each category will be announced in December, and the winners were be announced in January.