It should be significantly increased.
I used to think this way... but it is so regressive that it will really only hurt the rural poor while building shiny new freeways and trains for urbanites.
Instead, we should keep increasing fuel efficiency standards.
Raising the gas tax today is about changing behavior from personal transport to mass transit. And while mass transit is important in cities because of its efficiency... we can't soak the rural poors. Especially when the future is clearly not everyone taking trains... but self driving cars that ultimately will be incredibly efficient compared to today's cars.
And because self driving cars are safer and responsive, you can fit more cars on any given stretch of road. Increased traffic capacity without increasing the footprint of freeways in cities will make cities denser
without mass transit.
