Japan’s transport ministry plans to compel auto manufacturers to install fuel-efficiency recording devices on all their new models to more accurately determine their mileage ratings amid increased public skepticism.

The transport ministry plans to revise the related regulations as early as next week and apply them for new car models as early as October 2023, officials said.

It comes amid heated industry competition over producing better fuel-economy cars, and as manufacturers find themselves under pressure to shift gears toward a low-carbon economy.

It also follows concerns expressed over large gaps between the mileage ratings reported by manufacturers in car catalogs and on websites compared to what the numbers actually are once the rubber hits the road.

And as automobile makers ramped up their efforts in recent years to compete over fuel economy, the automotive industry became plagued by scandal over fudged numbers.

In 2016, it was reported that Mitsubishi Motors Corp. had illegally manipulated fuel-efficiency test data. That was followed by reports of another automaker having similarly manipulated data illicitly.

Consumer mistrust has been rising over the official mileage counts by car makers in part because they are measured under certain factory conditions without letting the cars actually run on the roads first.

The results tend to be inflated compared to the actual fuel efficiency the cars exhibit when driven on roads in towns and cities.

The fuel efficiency number that shows up in catalogs is measured based on the national standard, and its measurement is overseen by the National Agency for Automobile and Land Transport Technology under the transport ministry.

To determine the fuel-consumption figure, an inspector puts the car onto indoor testing equipment, runs the engine and spins the tires on a roller. It is assumed that the car is traveling on a straight road without the air conditioner or lights in use.

According to the Japan Automobile Manufacturers Association, some have raised concerns that a car’s fuel-efficiency rating is about 20 to 30 percent better than the reality on the road.

The transport ministry said it will not specify how companies should install the new measuring devices, but car makers need to make them unable to be deceptively recorded.

The data is expected to be recorded in computers mounted inside the cars, and will be calculated based on the driving distance and the amount of fuel consumed.

It will also require the real-time measurement of fuel efficiency, allowing drivers to see the number. 

All of the new car and motorbike models, excluding special types of cars, will be required to have the new recording devices installed.

The ministry aims to also require electric cars and plug-in hybrids that can charge from external power sources to record their “electricity efficiency” based on their electricity consumption. Hybrid cars normally need to record gasoline fuel efficiency.

The premise behind the new regulations is that if cars with better fuel efficiency are publicized, consumers will be able to choose more eco-friendly cars, leading car makers to develop vehicles with much greater fuel economy.

The transport ministry is considering collecting the data from the cars at time of inspection or during regular checks, with the car owner's approval.

But the ministry still has to sort out privacy issues arising from data collection and hurdles in making the data easily comparable.

The ministry will revise the related provisions for safety standards under the Road Transport Vehicle Law in early June, officials said.

Although some cars already have such a recording device installed, some car makers are asking for a preparatory period before implementing the new measures across the board.

The ministry plans to put the revised provisions for new car models into effect as early as October 2023, officials said.

Starting from September 2025, the ministry will extend its targets for existing car models.

The fuel-efficiency recording devices are already mandatory in Europe. The ministry has been discussing the policy change amid an international trend in that direction.

(This article was written by Masanori Isobe and Yoshitaka Ito.)