knotting, knitting, weaving and traffic flow

Background: [1] 

In the example at [2] , I am able to draw something resembling a knot: with overpasses and underpasses, and to use SMIL to drive a car along it. It works just about everywhere that has SVG/SMIL, I think.

Now, you'll note that the semantics of the path works fairly well since instead of breaking it into little pieces as in HTML (example [3] from 2002 ), it is one path. That is, the stroke-dasharray follows the curve as does the automobile.

Except for when we come to bridges. So, the questions are really three (I'll use letters instead of numbers, since I've already been using numbers for the footnotes):

a) Is there any way to get the auto to go under the bridge, short of making it become invisible for a time, either through opacity or through a mask? Such an approach is doable, but semantically funky, bordering on inaccessible.
b) You'll note that the speed of the vehicle spikes to infinity when it reaches an underpass (we might, thus,  anticipate metal fatigue). Is there a simple way to tell the animation to keep moving even though the path is discontinuous? (with an approach like in [4], using transparency gradients rather than M subcommands of <path>, I suppose this can be handled, but I'm still interested in the issue of what happens to an object when its animateMotion path is disjoint -- wouldn't it be nice to have the option of whether the invisible part is instantaneous or interpolated?)
c) Supposing that there is no easy answer to a) or b) then how will convince the World Fabric Conference, Knitters International, United Knot Theorists* or the World Highway Planning Commission to use SVG?

I suspect a little simple magic with something like z-index might help, but I haven't found whatever debates you may all have had on the topic.

regards
David

[1] http://srufaculty.sru.edu/david.dailey/svg/knots.html
[2] http://srufaculty.sru.edu/david.dailey/svg/notknot.svg
[3] http://granite.sru.edu/~ddailey/weaver.html
[4] http://srufaculty.sru.edu/david.dailey/svg/gradientweave.svg
* (United has the same letters as Untied)