They don't mention "flex". Hard things tend to be brittle. Having the only flex happening at the edges of the panels is suboptimal - that's where all the connectors are.
There's also the matter of fatigue. Aluminum, for example, is far stronger by weight than steel, but it is subject to fatigue in which microscopic cracks accumulate. These can often compromise virtually all the strength of a component before they're visible to casual observation (they can be detected via microscopy, x-ray, and sonic analysis).
I've had several aluminum components fail on me, suddenly, on bicycles. The experience is ... not particularly heartening.
Glass is similarly not known for being highly flexible or self-healing. Among the benefits of asphalt is that it has little internal structure and does reflow to an extent (more so under hot weather, often to the point of creating a hazard). Given the punishment taken by roads, this is a significant benefit.
I'd written an earlier critique after a bunch of posts sprouted on G+ and reddit: "Solar Roadways": either a scam or gross incompetence" http://redd.it/26on7y
As to this "clearing the air", it just reinforces that position.
"The point is that our highway infrastructure is in an embarrassingly antiquated state and the U.S. is no longer able to keep going with our current system of asphalt roads." These clowns keep dragging their goalposts all over the field. First it's cheap solar, now it's "the roads will pay for themselves" and "we need rugged infrastructure". The problems with this:
• Solar infrastructure which cannot pay for itself cannot pay for roads in addition to itself.
• There's an existing ruggedized highly-durable efficient roadbed technology for long-haul passenger and freight traffic. It does away, incidentally, with asphalt. It's called railroads: steel rails on wooden sleepers and gravel ballast.
"Solar Roadways is going to cost $60 trillion"
(NB: "dollars" is redundant if you're using the "$" symbol).
The $30-$60 trillion figure was arrived at using commercially available pricing for tempered glass. If Solar Roadways believes they can beat this cost estimate, the first thing they need to show is a cost of glass well below $300 per m^2 as Thunderf00t cited in his debunking video. That should be trivial. And yet they haven't.
"Asphalt roads are cheap and maintainable"
The question isn't "are present highways cheap or expensive?", but "does Solar Roadway's scam, I mean, scheme, actually beat those costs". I can point to all sorts of troubling things in the world, but unless the alternative I propose is actually BETTER then all the hurt presently felt doesn't improve my proposal one whit.
"We can't afford to heat roads"
Again, Thunderf00t: scraping snow and ice off of roads, and allowing blacktop to absorb solar radiation and converting it to heat with an efficiency of 100% to melt the remaining snow and ice is VASTLY less energy-intensive than applying heat of fusion to ice to convert it to water.
Again, SR's scam, erm, scheme, defends its proposal based on the undesireableness of the present situation, not on any actual merits of their proposal. For it has none.
On glass vs. asphalt: the question isn't the hardness of the materials, but on the durability with the added proviso that the material serve all its functions.
Asphalt has the primary requirement of remaining asphalty.
Glass would have to exhibit both the durability of asphalt and sufficient transparency to permit solar radiation to be absorbed and LED signals to be emitted.
Speaking of LEDs: the rebuttal fails to mention the most significant of Thunderf00t's critcisms:
• That much roadside signalling can occur with zero electronics or power requirements through passive reflectors. As is done today.
• That static, horizontally-mounted signage is sufficient for virtually all other circumstances. Where periodic signage changes are necessary (e.g., road closures), flippable signage can be used.
• If dynamic information is necessary, that can be provided with occasional electronic signboards, raised above the roadbed (for increased visibility) and with optimally targeted and shaded LED lighting (or variable reflective displays), which are fully legible in daylight. And at vastly lower cost than resurfacing every last inch of roadway in the nation.
And the rebuttal utterly fails to address the transmission line costs: $1 - $2 million dollars per mile, across the 23,000 miles of roadway, for another $23 - 46 billion dollars of cost.
It's still bullshit.
P.S.: As to why debunking this matters. Yes we've absolutely got some hugely challenging constraints headed our way, and some of the earlier ones aren't far off (NB: US EIA and the IEA both predict US fracked gas and oil will peak by 2020). Addressing energy needs is at the heart of many of these. Solar offers sufficient net total potential, the main constraints are cost and build-out. And there are other options out there I'd like to see pursued (wind, hydro, geothermal, maybe even nuclear -- I'm not a huge fan but if it provides a bridge or even permanent solution, so be it). And more hare-brained stuff such as Seawater Fischer-Tropsch Fuel Synthesis (SFTFS), which is a longer shot but passes my initial sniff test (it's also got the coal industry interested for some reason: http://redd.it/25iz78).
Solar Roadways is at best a distraction, at worst a scam that will be used against stuff that actually will work, or is actually worth pursuing.
The problems are getting people's hopes up over nothing, investors losing money to a scam, wasted investment, and even greater confusion and disinformation among the public. As bad as the SR people are, I find the press who've been shilling this on their behalf are even worse (I plan to assemble a Hall of Shame some time Real Soon Now). And it's a credit to amateur debunkers who've run the numbers and applied actual engineering knowledge to this, on Reddit, YouTube, G+, and elsewhere, who've put the so-called professional press to shame.