There is technology out there that will help people see what each trip they take in their car costs. Check out the Scangauge and EconoDriver. Scanguage is available in Canada here
Can you imagine how it might change people's habits if they had a cab meter in their car and they could see their money spent on gas vaporizing each trip they make?! It could be a great tool to compare cost of public transit to a private vehicle. After all we can't convince everyone to ride a bike because it is fun and healthy for you. Some people will react better to the dollars and "sense" approach.