In this blog post, we’ll examine the role of roads—which function like the blood vessels of a city—and explore how road scale and the number of lanes are determined based on traffic volume.
Roads are like the lifeblood of a city. Just as oxygen, nutrients, and waste products travel through our blood vessels, the movement of goods and people in a city occurs via roads, and urban infrastructure such as electricity and water is often installed or supplied along these roads. Thus, roads are essential to maintaining a city and are also spaces we use on a daily basis. We use roads every day when going to school, commuting to work, or heading out for leisure. And because most people in the city use these roads, they often become congested at certain times. Seeing roads jammed during daily rush hours makes us wonder: wouldn’t traffic congestion decrease if the roads were just a little wider? So, what are the criteria for determining the size of these roads?
There are many factors to consider when designing roads, but one of the most important is traffic volume. Traffic volume refers to the number of vehicles passing through a specific point within a given time period. In areas with high traffic volume, increasing the number of lanes to expand the road’s capacity is necessary to handle the heavy traffic, whereas in areas with low traffic volume, reducing the number of lanes is preferable to save on construction costs. However, traffic volume—which has such a major impact on determining road capacity—is not constant; it fluctuates frequently depending on the time of day, day of the week, and season. This is easy to understand when you consider that there are always many vehicles during rush hour, while streets are quiet in the middle of the day during the hot summer months.
Observing such unpredictable traffic volume naturally raises the question: “What should be the basis for determining road capacity?” If we base the decision on the time of day when traffic volume is highest, the road would never be congested—which would be ideal—but the need for more lanes would increase construction costs. On the other hand, if we base it on a time when traffic volume is too low, the road would be too narrow to handle the traffic. To determine this efficiently, standards have been established that take into account road capacity and service levels. The level of congestion and the state of traffic flow are evaluated as a “service level,” which is generally graded on a scale from A to F. When designing a road, a target service level is set, and based on this, the projected traffic volume is compared with the road’s capacity to determine the appropriate number of lanes and the scale of the road.
Traffic volume is usually measured and recorded directly on the road. However, in many cases where new roads are being built, there were no roads in that area previously. Therefore, it is difficult to accurately determine the traffic volume in such locations. For this reason, it is necessary to accurately forecast traffic volume. When forecasting traffic volume, the floating population and land use are predicted based on the extent of residential and commercial areas surrounding the road, and this information is used to calculate traffic volume. For example, when constructing a new bypass to alleviate traffic congestion on an existing road, one can utilize actual traffic volume data from the existing road and measured figures for the floating population in the surrounding area. However, in the case of roads being built in new cities or new urban districts, actual measurements cannot be taken because development has not yet taken place. In such cases, traffic volume is predicted by utilizing data measured in other cities that have a similar scale and characteristics to the planned new city.
Because roads occupy a large area and have a significant impact, once they are built, it is very difficult to rebuild or expand them. Furthermore, available resources are always limited. In South Korea, where available land is already scarce, it is not feasible to allocate large amounts of land solely for road construction. Therefore, it is essential to accurately predict traffic volume and design roads efficiently, taking into account the required functions and scale.
