One of the biggest hurdles to putting autonomous buses into practical use is "communication stability." When your smartphone signal drops, it's annoying; when an autonomous vehicle's signal drops, it can be a matter of life and death. Sotetsu Bus and NTT Docomo Business have run a trial in Yokohama for an autonomous bus that "keeps the signal from cutting out."

An Autonomous Bus Trial in Yokohama

From January 17 to 22, 2026, a notable trial took place in Yokohama, Kanagawa Prefecture. A consortium of eight companies led by Sotetsu Bus and NTT Docomo Business carried out autonomous-bus driving experiments jointly with the City of Yokohama. What set it apart was the combination of cutting-edge communication technology with a "road-to-vehicle cooperation system."

The test route ran a round trip of about 10.6 km, from Tsurugamine Station on the Sotetsu Main Line to Yokohama Zoorasia. On weekends the road gets congested with zoo visitors, and it includes narrow stretches where vehicles struggle to pass each other, a genuinely tough environment for autonomous driving.

Why "Communication" Holds the Key to Autonomous Driving

We all encounter weak signals and slow connections on our phones, but for an autonomous driving system, unstable communication is a fatal problem.

Autonomous vehicles exchange driving data and information about their surroundings over the network in real time. If communication drops or lags, it directly affects vehicle control and, in the worst case, could lead to an accident. Especially in "Level 4" driving, which needs no human driver, a remote monitoring system must know the vehicle's status at all times, making stable communication an absolute requirement.

Combining Several Advanced Technologies

The trial brought together several advanced technologies.

First is NTT's wireless optimization technology "Cradio." It predicts the quality of multiple wireless networks in real time and switches to another network before degradation occurs, keeping communication from cutting out. Alongside it, the "ISAP" traffic-control technology curbs video delay and image degradation.

"Local 5G" was also used. This is a 5G network built independently for a specific area without relying on a carrier, enabling stable high-speed communication even when it gets crowded.

There are innovations on the road side, too. "Smart road lights" equipped with AI cameras and LiDAR sensors were installed along the shoulder. They detect vehicles and pedestrians within 50 meters in a straight line and share that information with the autonomous bus in real time. This is the "road-to-vehicle cooperation system," in which not just the vehicle but the road infrastructure works together to support safe driving.

Solving the Problem of Passing on Narrow Roads

The trial used two small buses (Hino Motors' "Poncho") to tackle "passing control" on narrow road sections.

Passing control means adjusting movement so that vehicles heading in opposite directions can pass each other safely. On roads with poor visibility or limited width, even human drivers face difficult judgments, but by linking roadside sensors with the vehicles, the system aims to achieve automatic stopping, deceleration, and passing decisions.

It also tested "one-to-two" remote monitoring using Tokai Rika's system. Using docomo MEC, a single monitor watches two buses at once, an important test of whether autonomous buses can enable running multiple vehicles at once and reducing staffing.

The Pressing Backdrop of a Bus Driver Shortage

Behind this trial is a bus driver shortage that is growing more severe nationwide.

According to the Japan Bus Association's estimates, about 30% of bus drivers are projected to be in short supply across the country by fiscal 2030. Since April 2024, a cap on overtime work has applied to the transport industry as well (the so-called "2024 problem"), further accelerating the shortage. Service cuts and route closures are happening not only in rural areas but in cities.

With many route-bus operators running in the red, expectations for autonomous driving technology rise year by year. The government has set a goal of realizing driverless mobility services at more than 100 locations nationwide by fiscal 2027.

Aiming for Commercialization in 2027

Sotetsu Bus has been running Level 2 autonomous driving trials since 2019. In autumn 2024 it ran a small-bus experiment on an about 2 km stretch around Zoorasia; this time it expanded the distance more than fivefold, testing in an environment closer to real service.

The companies, including NTT Docomo Business, aim to commercially apply these communication and control technologies to autonomous driving services by fiscal 2027. This trial is positioned as an important step toward that.

During the trial, public test rides were offered on four days (January 17, 18, 21, and 22) by advance reservation, letting the public ride the autonomous bus firsthand.

Autonomous Bus Efforts Advancing Across Japan

The Yokohama trial is one part of a nationwide push to adopt autonomous buses.

The town of Sakai in Ibaraki Prefecture has run regular service since 2020, and the town of Eiheiji in Fukui Prefecture achieved Level 4 driving on public roads in May 2023. The city of Hitachi in Ibaraki Prefecture is also working toward commercial Level 4 autonomous service using medium-sized buses.

The city of Chitose in Hokkaido is running experiments in the harsh conditions of heavy snow and extreme cold, while the city of Sendai in Miyagi Prefecture is testing in coastal areas and mountainous zones where communication is unstable. Experiments tailored to each region's characteristics are being carried out around the country, building up know-how.

Challenges Technology Alone Cannot Solve

Putting autonomous buses into practical use depends not only on technical challenges but also on social acceptance.

Riders have said they feel "a sense of stability" and "can trust it," but running at a top speed of around 20 km/h can cause congestion behind the bus, raising the challenge of coexisting with ordinary drivers.

Even as autonomous driving advances, questions remain about non-driving tasks: helping elderly and disabled passengers board and alight, collecting fares, and handling onboard trouble. Full driverless operation is still some way off, and for now, introduction as a way to ease drivers' burden and address labor shortages is the realistic path.

What About Your Country?

Against the pressing challenge of a driver shortage, Japan is accelerating toward practical use of autonomous buses. Combining 5G communication with autonomous driving to achieve stable operation even on narrow roads and in congested areas, this trial is one answer to that challenge.

How is the adoption of autonomous buses progressing in your country? Is a shortage of public-transport drivers a problem where you live? How are communication technologies like 5G being applied to transportation systems? We'd love to hear about the situation where you are.

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