The Vehicle A-Pillar
The pillar between the windscreen and front door of a car is called
the A-pillar. This component is often reasonably large as it may be
required to 1. conceal wiring, 2. house an airbag, 3. allow easy access
for welding robots and 4. ensure that the windscreen can be replaced
easily if necessary. The A-pillar also has the adverse effect of reducing
visibility. European legislation allows for an "obscuration angle"
of 6 degrees. As a result, manufacturers have taken advantage of this
generous specification and in recent decades A-pillar thickness has
increased significantly.
In 2002 a study conducted by the Minnesota Department of Transportation
(MDT) found a correlation between lack of visibility and risk of collision.
Amongst their conclusions was the following statement: “…the
vehicle itself must be re-engineered to provide for better vision...”.
But, Safety is a thorny issue. A British DfT study entitled "Investigation
into 'A' Pillar Obscuration - A Study to Quantify the Problem Using
Real World Data" was published in September 2006 and as Dr Stephen
Ladyman stated in the House of Commons on 26th October 2006 the final
report was inconclusive.
Safety aside, obscured vision reduces driving pleasure. To help illustrate
how things have changed over the years, the view from a classic vehicle
- a Jaguar E-type - was captured using two cameras. These cameras had
lenses, similar in performance to the human eye, mounted with a separation
corresponding to average interpupillary distance. In a single photo
from one of the cameras, the A-pillar is clearly apparent. However,
when photos from both cameras are superimposed and the background is
lined up it can be seen that the A-pillar effectively disappears. What
one eye cannot see the other eye can and at distances greater than a
few feet from the vehicle there is effectively no obstruction to vision.
It is standard practice to quantify engineering matters. A-pillar thickness
has increased, typically, from around 5cm in the 1960s to 10cm or more
today. Dividing 10cm by 5cm allows us to deduce that A-pillars have generally
doubled in thickness. Quantifying the increase in A-pillar obscuration
is quite a different matter. Today all cars exhibit some form of A-pillar
blind-spot. Older vehicles often had an A-pillar blind spot that was effectively
zero. Dividing a finite quantity by zero quantifies the increase in A-pillar
obscuration as infinity!
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