It is now fairly common for carmakers, including Kia, Volvo, Hyundai and Ford, to test their autonomous vehicles on public roads. In 2013, however, Mercedes carried out the first autonomous journey in everyday overland and city traffic with its "Bertha Benz" S 500 Intelligent Drive research vehicle, which is now being retired.

Mercedes says that Bertha, named after the wife of Karl Benz and the first person to drive an automobile over a long distance, was "equipped with close-to-production technology and abundant computing power." Its journey took it along the same 100-km (62-mi) route from Mannheim to Pforzheim in Germany that Bertha Benz drove in 1888 and showed that self-driving cars weren't just a pipe dream, but were technically possible.

Less than three years later, a "highly automated" standard-production E-Class was awarded a license for an autonomous driving trial on the roads of Nevada, showing how quickly self-driving technology has developed. Despite this, the car is still not allowed to be left entirely to its own devices in everyday traffic, with a number of areas still requiring development.

According to Mercedes, the interconnection of sensors requires optimization and the sensors themselves can be further improved. They are still said to be highly dependent on the weather, with heavy rain and snow both continuing to pose challenges. The ability for autonomous cars to identify the relevant set of traffic lights at a junction where there are many is also reported to require more work.

Elsewhere, development is ongoing for vehicles to connect with each other and with surrounding infrastructure, as well as to recognize environments through image interpretation. Here, so-called "deep learning computers" interpret images not pixel by pixel, but in their entirety, making the capability transferable to any location.

Mercedes says that the responsibility for safe driving in autonomous vehicles will still be the driver's, with them able to take control at any time. Its aim, though, is to minimize reliance on the the driver by having the vehicle be able to act autonomously in stressful situations.

The "Bertha Benz" S 500 Intelligent Drive research vehicle is on show in the atrium of the Mercedes-Benz museum from July 26 until September 25.

The video below shows the 2013 journey made by the Bertha Benz car.

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