This would introduce a bias towards countries that are large and have extensive motorway networks. They would appear safer than countries that have a smaller portion of motorway miles.

> If we look at the number of deaths per billion miles driven, we see that motorways are roughly four times safer than urban roads, and more than five times safer than rural roads. This is not specific to the UK: among 24 OECD countries, approximately 5% of road deaths occurred on motorways.5 In almost all countries, it was less than 10%.