A Tesla Semi caught fire on Interstate 880 in Hayward, California, on Tuesday evening, and there was no crash. The electric truck’s lithium-ion battery burned long enough to keep the southbound freeway closed for about 10 hours.

The driver got out unhurt. But a Class 8 electric truck catching fire on its own, in traffic, is something Tesla and its growing list of Semi customers need to explain.

The driver told officers the truck caught fire and that they didn’t know why. No other vehicles were involved.

Northbound reopened Tuesday night. Southbound took much longer. CHP initially warned that the battery could burn for 15 to 18 hours, but crews beat that estimate, and CHP Hayward posted that all lanes were open at around 3:30 a.m. Wednesday.