A road is many things. Here are some of them.
A road is Movement. Every motorcycle, car, SUV, truck, or semi you see on the road is going somewhere. Those somewheres are never the same for any two cars. They are all going different places from different places, but for the time that you see them on the road, they have agreed to be on the same road at the same time and speed.
A road is Opportunity. The first turnpikes were financed by landowners along the turnpike route. They rarely made money from the stock they bought, but it did not matter. Having a better road to market would pay for itself quickly with opportunity, not stock dividends. When a new road is built, it opens up the land along that road to development. Development simply does not happen without roads. Lots of development requires lots of roads.
A road is an Agreement to not collide. This happens both incrementally at intersections and continuously in lanes. Because vehicles are steered, accelerated and braked by humans, lanes are wide enough to accommodate minor glitches in their steering. The standard lane is twice the width of the standard car, and 50% wider than the the average truck. You would feel real danger if the lanes were only 150% the width of your car, and would slow down accordingly. But that increased fear would get in the way of getting where you are going unfettered.
A Road is Access to places. All journeys need to end. You cannot drive your car to most places and just stop in the road, get out and walk to meet with people. Most commercial, industrial, and high density residential zoning codes require off street parking be provided to the users of that building. Assuming any American worth having got there by car, there would be no room on the street to accommodate all the vehicles that would come to these places, so builders and property owners have to cede much of their land and budget to parking. The land use is vital to the smooth flow of traffic. When you pull over to the curb, you are talking up space that could be used for traffic lanes. Get off the road when you want to stop, so everyone behind you can keep driving.
A road is a Killing Floor. Since the things moving on a road by default are all over a ton and moving faster than anything moved two centuries ago, getting hit by one is serious business. Since 1925, the road has been made safer by excluding everything but these heavy/fast things from the road, by right. If you get killed on the road, and the thing that killed you was not moving illegally or irregularly, then the burden of proof is on your next of kin to show that it is their fault at all. Getting killed by traffic is legally an Act of God. Tough Luck. Everything slower and smaller that wants to be in the road has to get permission, and disrupts the natural order of the road that has been in place since our grandparents were kids.
A road is designed to Stay Dry. Like builidngs, a road is designed to shed water. While buildings shed water to keep weight of their roofs and keep occupants dry, a road is designed to stay dry because the vehicles that use it need to have friction between their wheels and the road surface. Otherwise they will violate functions 1 and 2 of this list. Any water that falls on a road or a parking lot is jettisoned as quickly as possible for the sake of traction. Floating cars, or even cars with a thin layer of water under them, are not good for steering. So we must build roads to jettison water. Whether or not we try to stop that water before it ruins the closest steam is matter of how wealthy we are, and how important water is to us.
A road is designed to Support Weight. The average vehicle on the road is a ton and a half. Some vehicles are up to 40 tons, with two tons per wheel and almost ten tons per axle. This means roads have to be built with a thick section of asphalt concrete and gravel to support that weight. If a road is built as a simple layer of gravel or bare earth, heavy vehicles would sink into the roads or become mired in mud with tons of weight per axle. Too much weight on too little road will cause potholing, bulging and washboarding over time.
A road is meant to be smooth, but not too smooth. As the function of a road is to convey vehicles almost entirely running on pneumatic tires, a road much offer en0ugh roughness to provide grip but not so much that it provides rolling resistance. In the days of horses and wagons, the road was built for very different reasons. Then, a road was meant to offer grip for horse hooves more than a smooth way for wheels. The only place you would find a smooth road would be along the steel rails of the horse-car track. Even the road between the tracks would be rough, for the sake of the horses that had to pull the streetcars.
Roads Organize Space in America. We all think of our street address as where we live. Not our neighborhood, our lat-long coordinates, closest metro stop or watershed position, but our street address. The second most common default identity for Americans is where we do our shopping. Defined most often by swards of free parking, of course. Addresses a recent invention of the post office, but they highlight that roads do in fact organize our space.
A road is Life-blood. The way we’ve built for the last eighty years or more,the only way to get anywhere worth going and get people from everywhere is via road. The number of people who can walk to a place is necessarily smaller than the number that can drive there. The number of people who can walk places is even smaller in low density neighborhoods surrounded by roads and land uses hostile to bikers and walkers. So a road becomes the default life-blood to America’s places. You would be suicidal to not build for traffic to get to you, in most of America.
A road is a Utility Corridor. As one of the only presumed properties of the state, the road makes a great location for sewer, water, telecom, gas and electrical lines. Better to negotiate one permit to mess with pipes underground or lines overhead than hundreds. Since the roads organize space, where else to organize utilities?
A road is Open Space. It is a the largest, most durable sunny opening in some forests The species in those forests can not go around that clearing, so they must cross it. If they are unable to cross it, then that road fragments their population into two. Even the smallest roads will split smaller, slower moving animal and plant communities. An interstate highway can fragment even fast moving animals like deer or coyotes. They can get across miles away from the city, but each 4-lane highway crossing offers two opportunities to die for every animal that dares cross it.
A road is a corridor for more than cars. Predators and grassland species can move quickly up and down a road corridor in a way they cannot though unbroken prairie or nature. Seeds on tires get picked up and thrown off of tires and shoes. The weed species of America form one continuous and connected web over the United States, mostly along roads. Nest parasites and predators can use the roadway to scan the forest interior for prey within. This of course impacts the fitness of the species in the forest interior.
A road is edge. As I’ve mentioned before, the road id the most ubiquitous edge in the United States. Every road in the non-prairie US is an edge between open clearings and historic forest. The species that grow up on this edge are distinct from those of the lawn or open grassland or the forest interior. You will see trees grow differently on this edge, with branches and leaves along the entirety of their trunks, not just the tops. Vines and midstory weeds will exploit the whole canopy height for sunlight. They create a solid thorny wall against intrusion into the forest interior.
Disneyworld. The Magic Kingdom. Cinderella’s Castle in the middle of the top of the picture.
Disneyworld. Epcot Center. Approx. same scale