Leaving aside cycling and walking which work for reasonably active folk, on short journeys, in preferably clement weather:
- A small car costs ~ 12p per mile for fuel, ~25-50p all up cost
- A bus costs ~ 100p per mile - although very journey, ticket type dependant
- A taxi costs ~500p per mile - variable depending on time and location
Even if the price of fuel doubled, or a tax of 10p a mile imposed it would make almost no difference to the attraction, both cost and flexibility, of personal transport.
To reduce congestion and pollution needs a far more thoughtful and integrated strategy:
- reduce the need for travel. Smaller local schools, surgeries, hospitals, shopping, etc
- one teacher travels to a number of smaller schools, not 30 kids to a larger school
- change planning rules to sensibly mix employment, restaurants, etc with housing - not zoned as at present
- plan for imminent driverless on demand "pods" to reduce the need for vehicle ownership and parking
- reconfigure local services to meet new demands for work from home - local office pods, coffee shops, cafes etc
- and lots of other things I haven't even mentioned!
If you are truly rural or small settlement this will probably not work - but for larger villages upwards (population 2-3000+?) bringing more services locally minimises travel demand.