It is midnight on a Thursday, and three "sisters", which is how they like to be known, are sitting at a bus stop outside the Woodlands Town Garden.

The transvestites, dressed in heels and tight dresses, are not waiting for transport. Instead, they are on the look out for customers, waving men over with manicured hands - sometimes whispering "service, service".

On offer are sexual services costing between $30 and $50.

"Prices can be discussed," says one of the prostitutes, who is willing to reveal more details on the late night going-ons at the park.

The services are carried out in cars or in the park, if customers do not drive. "We also do it behind lorries," she adds.

Each customer takes about 20 minutes.

Most customers start arriving from 1am till about 3am, but some of the prostitutes start work as early as 9pm. Demand is higher on Fridays and Saturdays, and more of her "sisters" - as many as seven - will congregate there, says another transvestite.

One prostitute, who has been soliciting at the park for seven years, adds that it is mostly foreign workers who ask for their services.

"Very few Singaporeans. Some only come and see see and try."

The transvestites are usually Malaysians working full-time jobs in Singapore, moonlighting to save money for sex-change operations.

"There are some sisters who do it because they enjoy the sex and are lonely. There are very few places where people can accept us," says one.

They choose to solicit in Woodlands Town Garden because a number of them live near the Causeway, making it easy for them to return to Malaysia.

"Changi Village is too far and too crowded."

They say that the park used to be busier with more prostitutes but the authorities have installed more lamps and cameras in the past couple of years.

"Sometimes sisters get lazy and don't want to throw away the used condoms. Cleaners find them the next day and complain," adds one of the transvestites.

In two hours, The Sunday Times spots one car sitting idle, with dark moving silhouettes visible through the windows.

Another eight vehicles turn into the carpark, and make a couple of rounds before leaving.

A few drivers wind down their windows to speak to the prostitutes before driving off.

"After a while, you know the regulars," says one sex worker. "We become friends, and they visit us for some company. It's not always sex."

Aw Cheng Wei and Danson Cheong