At night, the LEDs would need powering from power stations. There isn’t enough to go round. 12 trillion LEDs would cost $1.4 trillion a year to run – or $5,000 a year for each American. They would double the power consumption of the country. LEDs only have a few years life expectancy, even when they aren’t being battered by traffic.
It’s another public/private partnership – in other words, the corporations take the profit from the spend. The people pick up the tab when it all falls apart.
Glass is a soft material, softer than most rocks. It will not be suitable to build roads from. Ground glass dust is not entirely healthy to breathe.