Over 11,000 athletes are due to participate the Summer Games next year, and almost all of are due to attend the opening ceremony on July 24.
With the athletes village some 20 kilometres (14 miles) from the opening ceremony venue, officials estimate it will take around 40 minutes by bus -- even if the current transport plan works.
"Balancing vibrant urban activities and management of the Games is an important subject for us," said Katsuhisa Saito, senior official in charge of the Tokyo 2020's transport strategy.
On Sunday the journey took about 10 minutes less than expected with no conspicuous traffic jams.
"The overall result looks good," said Saito.
Some roads surrounding the two venues were closed off to regular vehicles with exception of residents, while a partial ban on accessing the expressways was also introduced to avert congestion.
In total some 75 buses took part in the test.
Sunday was picked as a test date as traffic volume on the day is estimated to be about the same level as the Opening Ceremony, a public holiday.
Separately, Tokyo officials are calling for Japan's famously diligent workers to take vacations or work from home during the 2020 Games to avoid putting additional strain on the city's already notoriously stretched commuter routes.