Since the beginning of the week, vegetable fat has caused a kilometer-long blockage on the roadway of Autobahn 7 in southern Lower Saxony.
This was announced by the federal highway company on Thursday at a press conference.
It was initially suspected that the substance that ensures a slippery road is paraffin.
On Thursday afternoon, the A7 was still closed for around 50 kilometers to the south.
Another section should be released in the evening.
The motorway was closed between the Northeim-Nord and Staufenberg junctions over a length of around 60 kilometers due to the vegetable fat on Monday night.
Since then, cleaning work has been carried out with special vehicles.
According to an expert report, around 20 tons of vegetable fat, i.e. a complete truckload, were distributed on the motorway.
The culprit is still unknown.
The cleaning work is now progressing well because the cleaning method has been changed, it said.
In the meantime, 21 special vehicles are in use, which apply hot water at high pressure to the road.
In most vehicles, an alcohol-based cleaning agent is also used, which has to act on the road for 15 minutes and is then vacuumed off.
The vehicles are moving at 500 meters to one kilometer per hour.
Impatient drivers caused problems.
Because several people apparently bypassed the congested detour routes by using a section of the closed highway, junctions had to be monitored by highway company personnel.