The most dangerous roads are the roads having the highest ratio of a number of accidents to the amount of traffic, or accident rate, which is calculated as the number of accidents per 1 million vehicle-miles driven. Vehicle-miles driven represents the number vehicles on the given road * length of the road in miles. The discrepancies between accident rate in overall and regional views are due to the fact that overall analysis considers roads in their entirety, e.g. the whole of A49, whilst regional analysis focuses on the section of the given road in the given region, e.g. A49 in the North West.
The number of accidents only includes the accidents that have been reported to the police and doesn’t represent the totality of all road accidents and crashes. Data on accidents and traffic volume spans 10 years between 2007-2016 and has been taken from government sources: DfT Traffic Counts and Road Safety Statistics. Only the roads that have seen at least 1,000 accidents in these 10 years are included in the analysis.