The Park & Ride scheme, which was introduced in 1990 to reduce traffic congestion in the city area, is being reviewed and could be on the chopping block.
The scheme to encourage motorists to park their cars outside the Central Business District and take a bus or train to their offices has had a low take-up rate.
When asked if Park & Ride would be scrapped, the Land Transport Authority (LTA) said only that it is reviewing the scheme and "more details will be announced soon".
There are 42 Park & Ride carparks with a total of about 4,700 parking spaces across Singapore. But only about 40 per cent, or fewer than 2,000 of the spaces, are taken up each month - which the LTA has called "consistently low" for the past few years.
Motorists under the scheme pay $70 every month - $30 for a season parking ticket at a Park & Ride carpark of their choice and $40 for a travel card for use on the MRT and buses. The season parking ticket allows them to park between 7am and 9pm on weekdays.
The LTA said that only about half of the scheme's users take public transport immediately after parking their cars. "In other words, there are some motorists who have likely been using the Park & Ride scheme as a cheap form of parking, which defeats the purpose of the scheme," said an LTA spokesman.
Number of Park & Ride carparks, with a total of about 4,700 parking spaces across Singapore.
Percentage of Park & Ride carpark spaces taken up monthly - which the LTA has called "consistently low" for the past few years.
There is no penalty for doing so.
The misuse occurs at carparks near commercial hubs, such as at Block 842A, Tampines Street 82, and Block 156A, Toa Payoh Lorong 1.
When The Straits Times visited Toa Payoh earlier this week, it found at least two cases.
A 32-year-old civil servant, who wanted to be known only as Ms Lee, said she works nearby, so she passes the travel card to a friend, who reimburses her for the $40 value. "So I pay just $30 for parking. It's cheaper than normal season parking, which is around $70 to $90," she said.
SIM University senior lecturer Park Byung Joon said Park & Ride may become less relevant in Singapore as the island's rail system doubles to 360km in length by 2030.
The network will be "quite comprehensive" and commuters will have better access to an MRT line to take them to the city area, he said.
According to the LTA, by 2030, eight in 10 households will be within a 10-minute walk of a rail station.
Dr Park said: "Park and ride schemes work well in places such as the United States and Europe, where people commute from the suburbs to the main city. For example, in Chicago, they have some form of metro connectivity, but it's not so widespread."
He said the Government's ongoing $1.1 billion Bus Service Enhancement Programme, which will add 1,000 buses to the roads by next year, has also given commuters more travel options.
Still, for some commuters, Park & Ride has been beneficial. Mr Tan Wee Sheng, 41, a hospital executive, has been using the scheme for about 1½ years. Every morning, he drives from Tampines to Toa Payoh, leaves his car at a carpark there and takes the train to Novena. He said: "The scheme helps me save a lot. If I park at my office, it's $20 a day. But Park & Ride is $70 for the whole month."
He has considered taking public transport for the entire journey to the office, but said: "Since I already own a car, I can't just be parking it at home all day."