Quote:
Originally Posted by adam
Wider lanes gives drivers an increased *perceived* level of safety so they drive faster.
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Right on. This is often called
risk homeostasis. It's the idea that people have a certain perceived level of risk with which they're comfortable. If you make something feel safer, people will tend to take bigger risks to compensate for the increased safety.
The canonical example of this is the SUV that ends up lying on its side in a ditch after the first snowfall, because the driver thought "four wheel drive" meant they didn't have to slow down to account for the slippery road.
What makes risk homeostasis really significant is that, as adam implies with his use of the word "perceived" above, people are notoriously poor at assessing relative risks.
SUVs are a double whammy in this regard: they simultaneously a) feel safer than cars on account of their size and tank-like bearings, but b) are actually less safe than cars for both their occupants and for the occupants of other vehicles.
They have less responsive handling, longer stopping times, higher centres of gravity (making them more prone to rollovers), and less impact absorption engineered into their chassis.
At a more general level, risk homeostasis means that people driving on wide, straight roads with no obstacles will drive faster - so much faster, in fact, that their increased speed more than offsets the putative advantage of more streamlined road architecture.
This is why, for example, all those wide, treeless suburban roads tend to be both curvilinear and littered with stop signs: the road engineers made them wide and straight for 'increased safety', and then added the bends and stop signs in reaction to the fact that people were racing down those wide, straight suburban roads at high speeds.
Meanwhile, the residential streets of century-old suburbs are narrow, lined with curbside parking and overhung with mature tree branches - ostensibly a disaster-waiting-to-happen from a road engineering point of view.
The effect is to produce a strong perception in drivers that the street is
dangerous. There's barely enough room to pass an oncoming vehicle, a child could dash out between parked cars at any moment, and the branches of the street trees hang down low over the road, creating a feeling of being indoors.
As a result, drivers slow right down and the street ends up safer that the wide, treeless suburban road.
(That's not even to mention the fact that such a street configuration means people have to spend less time driving in the first place, and hence are at lower overall risk of injury and death from collisions.)
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