German self-driving startup Fernride said on Wednesday that it has raised $50 million in Series A funding to increase the use of its "human-assisted" autonomous freight trucks in customer's logistics yards.

The Munich-based startup had initially closed the funding round with $31 million, but had extended it due to high investor interest, the company said.

New investors include Munich Re's venture capital arm Munich Re Ventures, Bavarian venture capital firm Bayern Kapital and former Siemens executive Klaus Kleinfeld, who will become chairman of the board at Fernride.

Existing investors, including strategic investors HHLA and Deutsche Bahn unit DB Schenker also participated in the funding round.

Developing fully-autonomous vehicles that can go everywhere has proven harder and more expensive than expected.

But while many investors have backed off big bets on robotaxi and autonomous highway truck freight startups, they are and still funding startups targeting simpler self-driving vehicle solutions far removed from pedestrians.

Fernride CEO Hendrik Kramer said the startup is currently running tests with a small fleet of trucks for key customers including Volkswagen, DB Schenker and HHLA - all in confined, privately-owned areas at speeds of under 30 kilometres (18.6 miles) per hour.

Hamburg port operator HHLA, for instance, is using autonomous vehicles at the port to move containers, while Volkswagen is using them to haul semi-finished goods within its production facilities.

Fernride's trucks currently operate autonomously around 80% of the time, then remote human operators to step in to help the remainder of the time.

"Our hypothesis that you shouldn't pursue full autonomy, but a very high level of autonomy is very good ... and requires a human in the loop," Kramer said.

As the technology improves, Fernride's trucks will be gradually be able to operate autonomously more of the time and the company's customers will eventually start adding use cases outside yard operations, Kramer said.

(Reporting By Nick Carey; editing by David Evans)