Sweden is one of a very few countries where the police work with highway and automotive engineers to investigate bad crashes. The results of those investigations are quite differents from countries such as New Zealand where the police and highway engineers conduct completely separate investigations.

New Zealand police investigate individual crashes without considering other crashes at the same location. This prevents common factors from being identified and results in 95% of crashes being blamed on driver errors. Travelling too fast for the conditions is identified by police as a driver error in one-third of fatal crashes. However, when highway engineers investigate clusters of crashes they regularly find that the police identified travelling too fast for the conditions as the driver error in between one-half and three-quarters of fatal crashes at these "black spots".

The Swedish joint investigations found a similar pattern and concluded that two-thirds of these crashes weren't caused by speeding bad drivers. This is consistent with crashes that occur more randomly across the entire roading network. The Swedish investigators have concluded that only one-third of road deaths are caused by unlawful behaviour such as speeding, drunk driving and failing to wear seatbelts. This last point is most important because it doesn't cause crashes but does cause the resulting deaths. Following this logic leads to the basic argument in Sweden's Vision Zero road safety strategy that two-thirds of bad crashes are caused by ordinary drivers making ordinary mistakes just the same as in ordinary minor injury crashes. What makes bad crashes bad is not what the driver does to start the crash but what the car hits to complete the crash. Vision Zero focuses on how to reduce the severity of the collisions because this works for all bad crashes and not just the one-third caused by bad drivers.

In Sweden's bad crashes cars hit trucks, other cars and roadside objects in almost equal numbers. Because the Swedes already build some of the safest cars in the world there is little room for rapid improvement in this area. Because there is no known way of circumventing the relative mass ratio effect at open road speeds which makes head-on collisions between cars and even relatively small trucks inevitably fatal the Swedes have not wasted money or energy trying to make trucks more crashworthy in these types of crashes. Instead they are tackling both of these types of crashes by building three-lane highways with cable median barriers. The center lane alternates as passing lane in each direction.

Deaths caused by crashes with roadside objects are being reduced by reducing the number of roadside objects capable of causing fatal decelarations. Replacing narrow deep ditches with wide shallow ditches. Using frangible lighting poles and hollow-base wooden power poles (European safety standard EN 12767). Removing boulders, tree, etc. Where these methods are not possible or cost effective or where there are steep or abrupt roadside dropoffs then an appropriate type of safety barrier or wall is installed. The type of wooden barrier still widely used in New Zealand is not acceptable in Sweden. Sweden does have one major advantage over New Zealand: In the nine months of winter the Arctic highways are lined with natural snow banks which are very effective at gently slowing errant vehicles, although this may not be too important as most bad crashes happen in the more populous south.

The myth that only bad drivers cause bad crashes can increase the road toll in two ways:

1. None of us thinks that we are bad drivers therefore we will never cause a bad crash. While this makes us feel more comfortable it also makes us less careful because we underestimate the risk we pose to ourselves and everybody else.

2. It make us reluctant to pay for improvements to roadsides because we think that its only bad drivers who can't keep their cars on the road. In fact in most two-car crashes the cars don't stop at the point of impact because the collision angles and momentum involved allow the cars to keep moving, often still at very high speeds. Many of our modern safety systems like airbags, seatbelt pre-tensioners and parts of crumple zones will already have been used in the car-versus-car collision and may be of no use at all in a subsequent collision with a roadside object.