About 2/5 of Paris’ transport funding comes from the versement transport, a tax collected on salaries in the Paris region. The fees are highest – at 2.6% – in Paris and the neighboring rich département (similar to a county) Hauts-de-Seine; they’re lower, at 1.7%, in two poorer neighboring départements, Seine-Saint-Denis and Val-de-Marne. In the four départements on the edge of the region, the rate is 1.4%. Having the tax rate vary by location, with people who are more likely to be able to take advantage of public transportation paying more, makes a lot of sense. The region’s decision to tax the poorer départements bordering Paris at a lower rate also serves as a social equalizer, attempting to encourage investment in less-well-off areas.