An accident blackspot is a term used in road safety management to denote a place where road traffic accidents have historically been concentrated. It may have occurred for a variety of reasons, such as a sharp drop or corner in a straight road, so oncoming traffic is concealed, a hidden junction on a fast road, poor or concealed warning signs at a cross-roads.

For some decades treatment of accident blackspots (e.g. by signage, speed restrictions, improving sightlines, straightening bends, or speed cameras) was a mainstay of road safety policy, but current thinking has it that the benefits of these interventions are often overstated. Effects such as regression to the mean,
risk compensation

Risk compensation

In ethology, risk compensation is an effect whereby individual people may tend to adjust their behavior in response to perceived changes in risk. It is seen as self-evident that individuals will tend to behave in a more cautious manner if their perception of risk or danger increases...

and accident migration

Accident migration

Accident migration refers to a situation where action to reduce road traffic accidents in one place may result in those accidents resurfacing elsewhere.For example, an accident blackspot may occur at a dangerous bend...

 combine to reduce the overall benefit.

In some cases it has been claimed that the end result is an increase in overall casualties.
In one notable experiment, a number of accident blackspots were "treated" with a null treatment - placement of a garden gnome

Garden gnome

A garden gnome or lawn gnome is a figurine of a small humanoid creature, usually wearing a pointy hat, produced for the purpose of ornamentation and protection from evil sorcery, typically of gardens or on lawns....

, according to some reports. Accident rates at these points were found to have decreased significantly in the following period, a finding which is taken as clear evidence supporting the theory of regression to the mean.