Hundreds of men, women and children line the main arteries of the Indonesian capital every weekday, offering to ride in private vehicles during rush hours, when cars are obliged to carry at least three passengers on key stretches.
The "jockeys" -- as they are known -- do not stick out their thumbs like typical hitchhikers around the world. Here, one finger signifies a jockey working solo, while two offers a pair, usually a mother with a child in tow or a baby in a batik sling.
In a country where millions are struggling to climb out of poverty and into an expanding middle class the jockeys -- who charge about a dollar a ride -- have turned their services into a career.
Jimmy, 22, has jockeying down to a fine art. In the hodgepodge of roadside competitors waiting for a ride, he stands out with his silver-rimmed spectacles and blue chequered shirt tucked neatly into a pair of black trousers.
"Chauffeurs in BMWs and Mercedes cars often pick me up because I can pass off as their employer's friend or relative. Motorists don't want to get caught by police so jockeys have to help them minimise the risk," said Jimmy, who like many Indonesians goes by one name.
Cars picking up jockeys can face fines of up to one million rupiah ($109). But in a country where official corruption is rife, a 200,000 rupiah bribe is usually enough to get off the hook.
"Generally, nobody wants to get stuck in a jam with someone with smelly armpits. For my efforts, I ask for an extra 5,000 rupiah (54 cents) and I usually get it," Jimmy said.
He makes around five trips a day and pockets about $7.50 daily -- a good sum in a country where about half of the 240 million population lives on less than $2 a day.
But not all jockeys are as savvy or fortunate as Jimmy. Many female jockeys are often sexually harassed in private vehicles, and police regularly lock up riders in squalid cells. By law, they can be jailed for up to 12 months.
Nuraini, 39, has worked as a jockey for the past three years to supplement her husband's meagre income as a motorcycle-taxi driver.
"One time when I was still pregnant a driver asked if I wanted some fun. It was very uncomfortable so I quickly got out of the car," she said, carrying a baby in one arm and holding an eight-year-old daughter by the hand.
Nuraini rises at dawn to make the hour-long journey from her village in the suburbs to the city for the morning rush hour, returns home to cook for her four young children and is back on the streets to work the evening.
"It's exhausting. The weather can change from sweltering hot to terribly stormy. Some days, I earn nothing, even if I wait for hours," she said.
The jockeys know they are violating the law and could be fined or detained for several weeks if caught. But for the most part police turn a blind eye to the hundreds on the streets each day.
"I don't have a family. I never went to school. If I don't do this, how will I eat?" asked Praspardi Putra Wibisono, a 16-year-old who was arrested last year and detained for two months.
Herlina, 36, has been arrested twice and was detained for six weeks in 2006.
"My time in prison was terrible. Eighteen of us were crammed in a stuffy cell full of mosquitoes. We slept on thin bamboo mats and the toilet stank," she said.
"So, why am I still doing this risky job? Simple, I need to live."
The carpooling rule, introduced in 1992, has done little to ease the traffic snarl in Jakarta, which has a population of around 10 million.
During the week, millions more from the capital's outskirts join the rat race, meaning eight million cars ply Jakarta's streets every day, and at least 1,000 new vehicles are added daily to the grind.
Analysts warn that the city could become totally gridlocked by 2014 if major infrastructure changes are not made.