Tusimple has signed a deal to jointly develop self-driving trucks with volkswagens traton division, solidifying the san diego start-ups status as market leader in one of the fastest-advancing areas of autonomous vehicle technology.

Traton is also taking a stake in tusimple, making it one of four main investors alongside chinese internet group sina, us chipmaker nvidia and hong kong-based investment group composite capital. terms of the deal and the size of the stake were not disclosed.

The announcement follows news earlier this year that tusimple is making automated trucks with navistar in the us and working with partners including ups to start building a network of mapped routes and terminals to expand driverless operations nationwide by 2024.

Everything we are doing now clearly demonstrates were not in science project mode any more we are really focused on commercialising the product and business model, said cheng lu, tusimples president.

The driverless trucking industry got a relatively late start compared with self-driving cars but has not so far suffered comparable delays and setbacks. one potential advantage: goods travel on limited and often monotonous routes, removing the need for mapping out complex city centres.

The partnership with traton aims to build level 4 trucks that allow for completely driverless operations on predefined routes.

Tusimple has already been trying out its technology since 2015 with several million test kilometres on public roads and is a leading developer of autonomous driving, for example in the fields of perception and night vision, said traton chief executive matthias grndler.

When volkswagen sold a minority stake in traton last year, it priced shares at 27 each, but in march they fell below 12 and have recovered only to about 17.

Tusimple is widely expected to pursue its own public listing at a multibillion-dollar valuation within the next year.

Tratons choice to sign with tusimple may be seen as a snub to argo ai, the driverless technology group in which volkswagen and ford have a joint-majority stake.

However, mr lu said the deal was a recognition that the tech behind automated trucking differed significantly from that used for the passenger-focused, self-driving car industry.

Theres some overlap but everything a truck must do is much harder, he said. its 15 seconds to take a left-hand turn, versus four seconds for a car...[that level of difficulty] is why you havent seen anyone outside of tusimple demonstrate a class 8 truck, with a trailer, making an unprotected left-hand turn.

As the mass deployment of robotaxis has been delayed year after year, investors and tech groups have shifted their focus to trucking as a more practical use case.

Alphabets self-driving unit waymo is expanding testing and hiring for waymo via, the automated trucking arm it launched in 2017.

Aurora, a driverless group led by a trio of executives from google, uber, and tesla, said earlier this year its first commercial production would be in trucking.

Last year, daimler trucks purchased a majority stake in torc robotics, a rival to tusimple that has been helping caterpillar build driverless mining trucks since 2007.