Gas tax are the main source of highway and road money, but bonds are another big source. Every election cycle we in California have bond issues to pay for road work, and most of them pass. Many of them are for quite a lot of money. People don’t even mind paying for this since they know they are getting a smooth safe road for their money. It is when the money is hijacked or goes to transit they did not approve, or gets eaten away in useless environmental studies, or is spent inefficiently - that is when people get furious.
People don’t mind spending gas tax money & bond money for roads if they know their money is not being squandered and wasted or on a bridge to nowhere.
Bonds are not a source of funding, they’re a source of financing.
All the money produced by bond sales, plus interest, has to be paid back by taxes and user fees.