Why do the majority of sinkholes appear on roads and highways?

While laying roads, only the top soil is tempered or compressed. Also most of the water and sewage lines will pass through the roadway. So leakages from the pipelines weaken the soil. As the vehicle load and vibration increases day by day, the soil get much weaker and result in sinkhole. read more

There are two things going on here. One is what it says in the other answers, ie that pipes break under city streets and the leaking water can then undercut the roadways above. read more

The answer is we don't know, because we just don't have enough data. Sinkholes aren't widespread events like hurricanes or earthquakes. They're very localized. A lot of karst areas are agricultural, because they tend to have very good farming soil. And sinkholes happen all the time in farmers' fields. read more