The operator of the Tokyo train line that topped last year's congestion rankings in Japan is asking commuters to sign up for an early bird campaign to reduce overcrowding, offering participants a bowl of "soba" noodles as a reward.

Tokyo Metro Co., a subway network operator in the metropolitan area, said it would buy 3,000 passengers on its Tozai Line a 420-yen ($3.90) bowl of soba with a piece of "kakiage" tempura if the number of participants in the Jan. 21-Feb. 1 campaign reaches the goal.

[Corbis/Getty]

In order to get a soba voucher passengers need to take a Tozai Line train bound for the central Tokyo from a station between Toyokatsutadai and Monzennakacho in designated time ranges before 8 a.m. on all 10 weekdays during the campaign.

The highest congestion rating was logged on a section of the Tozai Line in a nationwide tally released by the transport ministry in July 2018. At its worst the trains were running at 199 percent capacity, which means passengers did not have the space to read a newspaper.

The company said if the total number of participants in the campaign is between 2,500 and 2,999 then those signing up will only get a 290-yen bowl of soba without the kakiage tempura.

If the number is between 2,000 and 2,499 the payoff would be a 130-yen piece of kakiage tempura, Tokyo Metro said, adding there would be no reward if less than 2,000 people sign up for the campaign.

The rewards can be redeemed at Metro An restaurants operated by a Tokyo Metro affiliate at certain stations in downtown Tokyo.

The campaign is part of efforts by operators of urban trains in Japan, most of which are notoriously congested, to encourage morning passengers to stagger their commuting hours.