That was when the city authorities, in a bid to attract drivers of private cars off the road, slashed the ticket prices on the subway -- by more than half in some cases -- and introduced a flat fare of 2 Yuan (30 U.S. cents) with unlimited transfers.

CNN: Beijing commuters feel the squeeze

Langton said families have been pleased with the pricing model because it often costs less to fly with children using the pay-by-weight model than it would to purchase flat-fare seats.

CNN: Pay-as-you-weigh airfares the 'next step'