Road and other hazard warnings -- good.
Folks who do a lot of highway driving might appreciate a warning that there's been a truck spill at milepost XYZ on route ABC (assuming Glass has its GPS stuff up, it'll know which "route ABC" warnings would be appropriate to your location), that there's a radarcop in the area of the next town, if they're getting a bit close to other vehicles, that there's a storm/ flash flood warning ten miles up, et cetera. I don't think I, as a bicyclist sharing the road who's been impacted by distracted drivers, would object to warnings-only (or other "critical to know") stuff running on Glass.
However, Glass won't stay confined to this realm (why should it? Passengers want to watch viddies). Perhaps as suggested above, there can be a "driving mode" that will only allow apps that have been tested/ proven to be truly warning/ alarm apps (and don't distract in "wait" mode) to run until driving mode is switched off (and if Glass is not in driving mode when a collision occurs, that should be easily determinable).
Of course, the advert possibilities could be interesting ("Hazmat spill at mile marker 29, police detouring traffic onto exit 5 during cleanup. This warning brought to you by XYZ Cancer Centers. Have a safe and pleasant journey.").