There is a gravel shortage in Costa Rica. At least what you might usually think of as gravel.
To make gravel, large rocks are normally crushed into fairly uniform pieces somewhere between the size of a grape and a golf ball then filtered through a screen to eliminate any softball, bowling ball or bathtub size pieces remaining.
Roads that are cut through clay, soil or sand are prone to being reshaped from smooth surfaces into cratered mud bogs under the influences of water and passing vehicles. A layer of gravel helps prevent the deterioration of the road surface because the small stones interlock and are more difficult to move around than sand or mud.
Round rock roads are the result of skipping the intermediate steps of gravel production (which require expensive machinery), scoop rocks out of a riverbed and just dump them on the road. The river rocks vary from pebbles to the size of a small pig, and form a roadbed that feels like a reject from a speed bump factory. The large rocks embed in the dirt, with about 1/3 of their diameter protruding above the surface.
Bicycling Over Mount Everest
For each meter of forward progress there are two or three 6 cm (2-3 inch) bumps. You can get some idea of how much harder the riding is if you consider that climb over all those little rock bumps adds up to a 9,000 meter (29,500 foot) elevation gain (and loss) on a 50 km ride.
That’s the same as riding from sea level to the top of Mount Everest and back down to sea level! Sounds unlikely, but if you don’t believe it do the math. It’s easy to see why we preferred almost anything to a round rock road.