Those modifications include stop — start (idle - off) systems in which the engine shuts down when the car is stopped during driving; low rolling - resistance tires (which are harder and thus less
flat, reducing friction); variable valve timing for engines, which increases gas consumption efficiency; and fuel economy computers or displays to encourage eco-driving, such as such as those in the Toyota Prius, which show miles per gallon
averages for that moment, hour, week or month, or when riding downhill, so that
drivers are more aware of how their driving impacts fuel efficiency.
From a transportation policy point of view, this sort of tax shifting is also more equitable in that it taxes every
driver according to the amount of miles they drive by sharing the price signal (by spreading the tax / fees burden) across all
drivers instead of assessing
flat road maintenance fees or concentrating them amongst a specific group of
drivers, some of whom just happen to use toll roads more frequently than
average but not necessarily drive more.