Tesla is working on electric, self-driving trucks that can travel in “platoons” or road trains capable of following a lead vehicle, according to leaked correspondence with regulators.

The electric truck, which is due to be unveiled in September by Elon Musk’s electric vehicle company, is close to prototype on-road testing, with both Nevada Department of Motor Vehicles (DMV) and California officials in talks to permit trials on public roads, according to documents seen by Reuters.

In an email to the Nevada DMV, Tesla sought permission to “operate our prototype test trucks in a continuous manner across the state line and within the states of Nevada and California in a platooning and/or autonomous mode without having a person in the vehicle”, which would be one of the first tests not including a human driver in the vehicle if permitted.

The correspondence and meetings with state officials show that Tesla moving forward in a highly competitive area of commercial transport also being pursued by Uber and Alphabet’s former Google car company, now called Waymo.

While Musk has previously stated aims to build an electric truck, Tesla has yet to announce any autonomous driving aims for the vehicles, which are seen as the next evolution of greener and safer road freight. Tesla has been a leader in developing self-driving technology for its luxury cars, including the lower-priced Model 3, which it is beginning to manufacture.

Several Silicon Valley companies developing autonomous driving technology are working on long-haul trucks. They see the industry as a prime early market for the technology, citing the relatively consistent speeds and little cross-traffic trucks face on interstate highways and the benefits of allowing drivers to rest while trucks travel or the removal of human drivers altogether.

Some companies also are working on technology for road trains, a driving formation where trucks follow one another closely. If trucks at the back of the formation were able to automatically follow a lead vehicle, that could cut the need for drivers.

Silicon Valley startup Peloton Technology, for example, is working with several truck makers including Volvo on its so-called platooning or road train system, which it sees as a precursor to autonomy.

While established trucking companies and truck manufacturing startups have poured resources into electrifying local package delivery fleets, battery range limitations have largely kept the industry from making electric trucks that travel across swaths of the country.

Venkat Viswanathan, a lithium ion battery researcher at Carnegie Mellon University, said that electric long-haul trucking was not yet economically feasible yet, and that the massive batteries required to compete with the 500-mile range of diesel trucks would limit cargo carrying capacity.

Tesla declined to comment on the matter, while Nevada officials confirmed that the company had not yet been given a license for the testing.