When the school bus stops, all other vehicles around have to stop too. Speed limit signs exist that are not found anywhere else in the world. There are dedicated lanes for carpools, laws permitting traffic overtaking on the right, and lane markings consisting of raised “dots” instead of painted lines. Road traffic in the USA makes many specific demands on the sensor systems and algorithms of vehicles equipped with automated and autonomous technology. The aim of the Intelligent World Drive on five continents was to gain worldwide insight into real traffic conditions so that future, more automated driving systems can be adapted to country-specific traffic and user habits.
The automated test drives in the greater Los Angeles area, and subsequently to the Consumer Electronics Show (CES) in Las Vegas, concentrated on the assessment of driving behaviour in dense city traffic and on highways. The focus was particularly on the recognition of school buses, lane markings, and speed limit signs. In addition the innovative DIGITAL LIGHT system was tested.
Stopping when the school bus stops and dedicated lanes for carpools
School buses are unique road users in the USA. As soon as they stop and switch on their warning lights, all vehicles in the immediate vicinity must also stop. No vehicle is allowed to pass – even in the opposite direction. Vehicles equipped with automated and autonomous driving technology must be able to distinguish school buses from all other vehicles, and recognise when they are stopping to let children get in and out.
An equally demanding task for camera and radar systems is identifying separate carpool lanes, which are reserved exclusively for vehicles in which at least two people are sharing a ride. These so-called HOV lanes (high-occupancy vehicle lanes) can be found on multi-lane interstates and freeways in urban areas. For the sensors and algorithms of automated and autonomous driving technology, it is difficult to recognise these as special lanes and distinguish them from normal or exit lanes. Moreover, the lanes are not always in the same position, and can be on the left, right or centre of the highway. HOV lanes can also be separated from the other lanes by two uninterrupted yellow lines, or by metal guard rails, or they may be identified by painted diamonds. In the future, autonomous driving will also require that the system knows the number of occupants in the vehicle to ascertain whether they are permitted to use the carpool lane. This is because in metropolitan areas, there are also HOV lanes that are only permitted for carpools of three or more (e.g. Los Angeles) or even four or more persons (e.g. New York).
Raised dots as lane markings
The so-called Botts' Dots are a further challenge for the sensor systems and algorithms of vehicles equipped with automated and autonomous driving technology. In many US states, these plastic or ceramic dots are used to mark driving lanes on highways instead of the usual painted lines. Driving automation features such as Active Lane Keeping Assist and Active Steering Assist must be capable of consistently recognising them in order to operate dependably, which is a challenge. With an eye to facilitating the fully-automated driving of the future, the US state of California is planning to harmonise all lane markings and to gradually remove the Botts' dots, which are believed to total around 20 million in all.
Furthermore, US speed limit signs are just as unique. They have a completely different shape and size than in Europe, Australia, Asia and Canada, and even within the USA, the design of speed limit signs can vary.
Testing the innovative DIGITAL LIGHT
In addition to the features specific to the country, Mercedes-Benz tested a headlamp prototype featuring the innovative DIGITAL LIGHT technology in California and Nevada. The non-glaring, continuous high beam in high-definition quality uses chips with over one million micro-mirrors, and therefore pixels, per headlamp. As such it achieves ideal light distribution in any driving situation – without glaring other road users. Furthermore, this revolutionary lighting system makes functions possible that were unveiled as a vision of the future in the F 015 Luxury in Motion research vehicle in early 2015. Among other things it is able to project light symbols or objects onto the road in order to communicate with its surroundings.