BTW as most people know it doesn't make a difference how BIG a car is to how SAFE it is. The old mini is a 4 star safety rating (the new should be even better) and the range rover a 4 star safety rating ( adult occupancy). Slight difference in size
But I do see where people are coming from with the estate boot and white van drivers
Mel, the physics of collisions between cars is fairly well understood. Conservation of momentum means that the heavier the vehicle, the less its overall change in momentum in a collision with another vehicle. Because of this, in a collision between a heavy car and a light car, the passengers in the heavy car will experience smaller deccelerative forces than those in the light car, and so will be less likely to be injured. Those same deccelerative forces can be reduced by clever design (crumple zones to absorb some energy and thus change the coefficient of restitution, airbags to reduce the decellerative forces which apply to your head inside the car, etc), but the physics remains the same - you are safer in a heavier vehicle (you'll take a smaller portion of the change in momentum in the first place), and safer still in a heavy vehicle with large crumple zones which absorbe some of the energy.
Think of it another way - in a head on collision, would you rather be in a 1950's HGV, or in a Euro NCAP 5 star rated 2007 MINI? Common sense (and physics) says sit in the HGV. Safety ratings are good at informing you which cars within the same vehicle class are safest (i.e. best designed), but they don't tell the whole story when it comes to a collision between vehicles in different classes on a real road.
To illustrate the role of vehicle weight in the physics of crashes, consider a head-on collision between two cars. If the two vehicles are of unequal weights, the heavier vehicle will drive the lighter vehicle backward during the crash. Thus, in a head-on collision when both vehicles are traveling at 30 mph and one vehicle weighs twice as much as the other, the passenger compartment of the lighter vehicle will be decelerated from 30 to 0 mph and then accelerated backward to 10 mph. The sudden speed change during the crash will be 40 mph for the lighter vehicle, but the heavier vehicle will experience a speed change of only 20 mph. Because of the greater speed change, the occupants of the lighter vehicle will experience much higher forces than the occupants of the heavier vehicle and, therefore, will be exposed to a higher risk of injury.
So the point of my post is that on a busy motorway, size does matter, and for this reason, I would not hand on heart recommend a MINI for a daily 80 mile motorway treck on the grounds of safety alone. I would instead recommend something heavier and with more metal to absorb some energy in the event of a collision
Quote from Correlation Of NCAP Performance With Fatality Risk In Actual Head-On Collisions
If car 1 and car 2 weigh exactly the same, and both drivers are the same age and sex, the likelihood of a driver fatality in a head-on collision would be expected to be equal in car 1 and car 2. If car 1 and car 2 have different weights, etc., it is still possible to calibrate formulas predicting the expected fatality risk for each driver in a head-on collision between the two cars, as a function of each vehicle's weight and each driver's age and sex. The formulas measure the relative vulnerability to fatal injury of the two drivers, given that their cars had a head-on collision. The risk is greater in the lighter car than the heavier car, and a female or older driver is more vulnerable to injury than a male or younger driver. For example, given 100 fatal head-on collisions between 3000-pound-cars driven by belted, 20-year-old males and 2500 pound cars driven by belted, 50-year-old females, these formulas predict 10.8 times as many deaths among the older females in the lighter cars as among the young males in the heavier cars.