You are driving along the road when the dotted white line that has been your companion - separating your car from oncoming traffic - suddenly disappears.
One theory is that you will slow down, making the road safer.
Speed reduction
The first trials to remove the central white line from roads were held in the UK more than 10 years ago.
Wiltshire County Council stopped repainting some lines when roads were resurfaced between 1997 and 2002. The authority concluded there were safety benefits to removing it on roads with a 30mph or less speed limit.
White lines have since disappeared on about 20 roads in the county.
More recently sections of three roads - one in central London and two in Croydon - had their lines removed as part of a small trial, which began 2014.
Transport for London (TfL) suggested there has been a "statistically significant reduction in vehicle speeds" as a result of removing the central markings.
Speeds reduced by as much as 8mph in one road, it added.
In Norfolk, trials have been held in rural villages and are being expanded into built-up areas.