This is like, but not exactly the same as, growing diamonds by starting with small seed pieces and growing them with more carbon.
_There might be safety problems, since nanotubes are like needles, can pierce surfaces, and then stick, as well as behaving like aerosol. They may clump deep within the lungs, or act like asbestos or other fine mineral fiber. This would be primarily a concern during manufacturing (of composites), and destruction (of material), whether it be during disposal/recycling, or violent incidents intentional or accidential.
_Surfaces of nanotubes are also almost friction free, and might prove to be a challenge to keep from slipping and sliding around within a matrix. Molecular branching, nanotubes with U shapes, or hooked ends to facilitate mechanical interconnection of nanotubes at the molecular level and remedy this issue.
_The use of C2H6 may prove interesting, since it is a raw material already in demand for polyethylene. Perhaps it might replace it in certain products. SPECTRA shield (Honeywell), made of polyethyene fiber, is the backing of Interceptor SAPI plates. Higher strength, potentially afforded by lighweight nanotube composites, backing and body armor material may make Interceptor system better, or obsolete.
_Other than that, this might pave the way for affordable, light, high quality, high strength material for a plethora of uses. A carbon fiber aluminum alloy NASCAR cage, w/an abundance of airbags, could make A and B segment cars prectically indestructible vs all current road vehicles. This would eliminate the last reservations about crash safety of small/mini cars. All vehicles could be lighter, 30-50% lighter. A 2+ton 24mpg large MPV would become a 2,100-3,000lb vehicle w/fuel mileage of a good modern B car.

Nano-science marches on. But Allen's prediction of the super-safe mini-car don't make sense to me. Yes, the car's safety cage would be strong. But wouldn't the technology be prohibitively expensive? More importantly, this still does nothing to "ride down" the force of an impact through material distortion. If anything, a crash using such a cage would register higher G forces. Mini-cars need much work in deformable structures to overcome rational safety concerns. In addition, we need to see investment in Ford's inflatable safety belt, stronger pillars, roofs and foot boxes using high-strength steel, better headlights, higher standards in braking, and a sensible built-in limit to top speed dependent upon driving zone via short range transmitter.

JC:

You have a good point. Making the box lighter + stronger will translate into more driver confidence, more speed, more loss of control and more accidents of all types.

Road casualties, presently at about 50 times the Irak war rate, seem to creep up and match the number of vehicles on the roads and streets.

Speed, cell phones usage, driver negligence-foolhardiness-inexperience, poor road condition and design etc cannot be overcome with lighter-stronger materials.

Some kind of automated systems to reduce the speed and even stop the vehicle when known dangerous factors occur would help.

JC -

well-designed composites can actually absorb far more energy via delamination than metal parts can via plastic deformation (except for localized buckling, but that is only possible for a limited set of crash scenarios).

Harvey D. -

making a vehicle lighter does not necessarily increase its top speed. After all, you can fit a less powerful engine. Active safety systems are popular gadgets these days, at least in luxury vehicles: ABS, ESP, look-ahead radar, infrared cameras, head-up displays, adaptive cruise control w/ crash anticipation, curve lights, lane deviation warning systems, cameras for blind spot and parking, self-deploying rollover guards in convertibles etc.

Of course, none of these measures is a substitute for an alert and defensive driver. Too many traffic accidents are caused by alcohol consumption, drowsiness, distractions incl. misbehaving children and phone calls as well as unsafe speeds in inclement weather and/or terrain. Mechanical failure is rarely to blame and then usually only as a result of poor maintenance.

It would indeed be useful to couple acceleration and rotation sensors with differential GPS, navigation computers and road condition data broadcast received via reliable multicast. This would allow the vehicle to identify certain unsafe driver behavior patterns and issue warnings and/or take fail-safe action. This might be especially useful for at risk-drivers, e.g. teenagers, college kids and senior citizens.

If vehicles actually broadcast their position, compass heading and speed to the traffic around them, each could maintain a dynamic map of its immediate neighbors. Of course, the success of such a system depends on the software's ability to infer the likely location of any vehicles that are unable or unwilling to participate. For privacy, the standardized communications protocol would on a crypto hash of the VIN plus the timestamp of the last engine start. This is virtually guaranteed to be unique.

Lucas,

Imagine a side impact into a carbon fiber door panel. The occupant would be subject to a hail of high speed chards. To offset, the standard un-armored airbag would be shredded, and also forced toward the occupant.

Without consideration of cost, what you've done is to have a bunch of CAD fun designing your car. I'm interested in practical, do-it-ASAP measures to build our sustainable future, the only one worth living in. It's hard for me to imagine kevlar or carbon fiber being used for mass-produced major automobile structures, nevermind carbon nano-structures. I CAN imagine a mixture of plastic and some cheap, small, hollow structures which blooms or is blown into a matrix. Such a mystery material must be cheap enough to be widely used. What is obvious to us both is that any lower mass alternative to steel or aluminum will have to be engineered to smoothly decelerate the vehicle upon impact. Small cars have a big job to do in keeping us safe.