So a motorcycle pays, say $10. A two-seat car pays $20, a sedan pays $40 and an SUV with seats for 6 pays $60. An RV? $100.
Those fees mean that bigger cars -- less convenient cars -- pay more. It also gives people (free!) an incentive to share cars when visiting the park.*
Bottom Line: Parks are nice but traffic jams are not. Use GPP to get more people and fewer cars into parks.
* And policy matters:
God has cared for these trees, saved them from drought, disease, avalanches, and a thousand straining, leveling tempests and floods, but he cannot save them from fools —- only Uncle Sam can do that. -– John MuirMuir may have relied on hoped that Uncle Sam would save the trees, but Uncle Sam also encouraged their harvest. (I can't find a nice time series on timber harvests, only that it peaked in California in 1955; many of the harvested trees were redwoods. Anyone?)