The three pedestrians, believed to be sixteen, died at the scene at Shepiston Lane, Hayes, on the M4 Junction 4, near the Esso petrol station. Some other teenagers who were part of the group by the bus stop were not injured.
Police said it is not being treated as terror-related.
Police and ambulance services went to the scene after they were called at 8.41pm last night after reports of a “serious road traffic collision” involving a black Audi.
All of the next of kin of the deceased have been informed. The victims not yet been formally identified.
Detective Jane Shaw, of the Serious Collision Investigation Unit, said: “These are horrific circumstances that have resulted in three young people losing their lives; I need anyone who saw what happened to contact police immediately.
"Did you see this Audi before the collision, or in the moments leading it up to it? I would urge you to speak to us to assist us with our investigation."
The Met Police said in a statement: “A group of teenagers were standing near a bus stop when a car, a black Audi, is believed to have collided with three of them.
“Despite the best efforts of officers and LAS, all three died at the scene. While we await more information, the victims are all believed to be teenage males, aged approximately 16.
“A 28-year-old man who was inside the vehicle was arrested and then taken to a west London hospital for treatment. He will be taken into custody once he is discharged.
“At this early stage, enquires are ongoing to establish exactly what happened and whether there were any other occupants in the vehicle.”
Road closures were put in place while the incident was dealt with but have since been lifted.
Officers from the Met’s Roads and Transport Policing Command investigate.
Anyone who witnessed the collision is asked to call the Serious Collision Investigation Unit directly on 0208 991 9555 quoting ref 7843 of 26 January, or call 101 or tweet @MetCC.
Alternatively, contact the independent charity Crimestoppers on 0800 555 111, or visit crimestoppers-uk.org.