The dramatic CCTV footage shows driver Mohammed Khalique battling with the controls as the double decker careers through a junction at speeds of up to 40 mph before smashing into the back of a car.
Three people were seriously injured, including one passenger who broke his back and the bus driver who was cut free from the wreckage.
Twelve others suffered minor injuries in the collision which involved two other buses and three cars near Sloane Square in September 2013.
The CCTV evidence was obtained by the Standard today after Mr Khalique, 60 from Newham, was cleared by a court of driving without due care and attention, a charge which he denied.
A judge at Bexley magistrates court said he could not be sure whether the driver or a “computer glitch” had caused a malfunction in the high-tech vehicle.
The court saw CCTV footage from the new Routemaster, nicknamed the Boris Bus, as Mr Khalique frantically tried to control it for about 40 seconds.
District judge Dennis Lynch said the incident was “truly terrifying to those looking at it and must have been even more terrifying for those directly involved, particularly Mr Khalique.”
The prosecution claimed Mr Khalique mistakenly pumped the accelerator instead of the brake and a Transport for London report discounted computer malfunction.
However, the defence argued the computer control systems controlling the brakes failed and Mr Khalique tried to control the vehicle.
Two expert witnesses told the court their analysis suggested the crash resulted from electrical failure in the £354,000 Wrightbus manufactured buses which started service in 2012.
The court heard that the lunchtime accident happened on the Aldwych-bound 11 route, operated by Go Ahead London.
The bus speeded up after pulling out in Lower Sloane Street and missed a car at a crossroads before crashing into stationary traffic in Chelsea Bridge Road.
Mr Khalique told police he tried the engine isolator and brakes, which were “completely dead”.
In a statement to police he said: “As soon as I pull out bus is going like a bullet, it’s generating itself speed.”
He feared applying the handbrake would flip the bus, adding: “I thought I’m going to die that day.”
Witness Steve Greensword was on-board with his two children and broke his back when the bus crashed into the back of cars. He told the court: “I ran back to try and protect my children.
“(Mr Khalique) kept saying: ‘I have no brakes, I can’t stop.’”
PC Adrian Armstrong, a Met forensic collision investigator who examined the bus, told the court evidence suggested Mr Khalique mistakenly pumped the accelerator instead of the brake.
This caused “maximum acceleration with no braking whatsoever,” PC Armstrong said.
The court heard Mr Khalique, a married father and bus driver for 13 years, was a cautious driver with a good record who was driving “very slowly and steadily” before the crash.
Sensors showed the brakes working normally beforehand.
Four other drivers told the court they had experienced technical problems on the new Routemasters, including on-board computer failure, loss of power, and the steering and brakes locking up
But engineering reports showed no logged complaints of brake failure on Boris buses, although there had been other computer problems, including 18 upgrades to the air conditioning system.
Finding Mr Khalique not guilty, district judge Lynch said: “I cannot be sure that it was Mr Khalique at fault, rather than an unascertained, potentially crucial, computer glitch.
“I cannot be sure beyond reasonable doubt that it was your driving at fault.”
Speaking afterwards, Mr Khalique, who has left the company, said: “I’m ok now, but this last year has been really stressful.”
Leon Daniels, TfL’s managing director of surface transport, said: “New Routemaster buses remain a safe and valued part of the capital’s transport infrastructure.”