US electric carmaker Tesla is adamant its self-driving technology is sound and will continue to improve after the first fatal crash involving its automated vehicles.

The autopilot function is under investigation by the US National Highway Traffic Safety Administration after the death of a Tesla Model S driver.

“As more real-world miles accumulate and the software logic accounts for increasingly rare events, the probability of injury will keep decreasing,” Tesla says in a blog post.

“Autopilot is getting better all the time, but it is not perfect and still requires the driver to remain alert. Nonetheless, when used in conjunction with driver oversight, the data is unequivocal that autopilot reduces driver workload and results in a statistically significant improvement in safety when compared with purely manual driving.”

In the fatal crash in May, the Model S was on autopilot when it hit a truck that veered into its lane.

“The system makes frequent checks to ensure the driver’s hands remain on the wheel and provides visual and audible alerts if hands-on is not detected,” Tesla says. “It then gradually slows down the car until hands-on is detected again.

“We do this to ensure that every time the feature is used, it is used as safely as possible.”