Trick of numbers : stats have a meaning ONLY on very large numbers.
A black spot is an area where 5 falatities occured the 5 last years: black spot change every year.
Alerting on black spots: USE CASE
Road #N13 (France) between Saint Germain en Laye (NEXYAD office) and Paris La Défense : 160,000 vehicles per day. Then 58,4 million vehicles per year. Then 292 million vehicles in the last 5 years.
Let’s say that there is a black spot on this segment: a maximum of 5 vehicles (maybe less) had an accident with fatality… because one accident can lead to several fatalities.
Vehicles with no fatal accident : (292 million – 5) vehicles that didn’t have this problem…
The black spot is mostly a safe zone.
Observed frequency of fatal accident on the black spot: 5/292 million = 0,000000017 which means that on a black spot, fatality almost never happens.
Do you really want to be alerted for something that almost never happens?
=> Black spots recording (on maps) is not relevant for road safety alerts!
