Ding v. Prévost, A Division of Volvo Group Canada Inc.
 The bus was a monocoque design also known as “unibody” or “integral”, as
opposed to a body-on-chassis design. At the risk of oversimplifying, the latter
involves a ladder-type frame on top of which a bus body is attached. One of the
main differences between the two is that the unibody design has crumple zones
which are meant to absorb energy in a crash. As described by Mr. Bolduc:
Well, a body-over-chassis behaviour would be a little bit like -- and I will talk
about image to help. If you take a baseball bat and you drop it to the floor it
will bounce back. So this means that the structure itself does not absorb a lot
of energy. All the energy is transferred. On the other hand, a monocoque
structure is built of a lot of small components. See it a little bit like if you
would take any shape you want to create in a monocoque, and you would
take a web, a spider web, and you wrap it around. So you're talking about a
larger, more complex structure where all the components will be oriented in
the direction of the forces you want to address.
And when you have a collision or when there is an impact, those smaller
components, compared to the larger beam, will start to bend and they will
start to absorb the energy. So therefore, it will not bounce back all this energy
either to the passengers or to the car in front or the other -- so it will absorb
as it gets bended and gets deformed. So basically in terms of dynamics of
accidents, this -- the monocoque structure is a more complex but more
energy absorbing structure.
 Mr. Bolduc said that in North America, the industry moved from chassis to
unibody construction 30 to 50 years ago.
 Passenger protection was provided by what was termed in the industry as
“compartmentalisation”. The first element of this was the monocoque design which—
as I have set out—was designed to absorb impact in a crash. Mr. Bolduc described
the balance of the concept:
[Y]ou see that as a bubble around the passenger, a little bit like you would
have an egg in its crate. So in this area you will try to have smooth
components. No tubing, no steel pipes. You will try to keep that person in its
seat. So a coach with the compartmentalization strategy would have -- well,
the seat in front will be high. So a high back in front of you that will collapse if
you put pressure to it. It will absorb energy if you're moving there. You will
have armrests on each side of you. So it keeps you in this area. You would
have a foot step where you put your foot, but the minute that you put your
foot there, you're better braced if something happened. The hat rack on top of
your head will have carpet into it. So the idea is to have a soft shell around
the person. So that was the approach of compartmentalization, keeping the
people in this shell surrounded with smooth or energy absorbing material.