Once the work of gathering data regarding road usage has been done the monumental task of analyzing it begins. In order to make sense of the numbers highway engineers will employ a number of different analytic methods to determine the needs of the community and what the best construction methods and design for a highway will be. In addition, the people planning a new highway will need to develop a model that can predict future traffic patterns so that new roads don’t become a bottleneck in a few short years.
When analyzing traffic data, there are three distinct levels that engineers will investigate. It is important that at some point they consider each vehicle on the road as a unique individual unit. This form of analysis is called microscopic scale and is the main method used by highway engineers to determine the causes, frequency, and severity of traffic jams. When looking at information like average speed or the density of cars on a road engineers and analysts are using macroscopic analysis. This is important because having data on every single vehicles speed and information specific to every vehicle isn’t always practical or even useful.
For this kind of information, aggregate values are used such as the average speed of all vehicles at a given time. The final scale of analysis is called the mesoscopic scale and is a more modern but less used form of analysis that tries to look at traffic patterns as kinetic equations.
In addition to looking at how the flow of traffic works and designing roads that improve the flow of vehicles, it is also important for highway engineers to analyze the potential environmental impact of new roads. Road surface is non-permeable meaning it has a profound impact on groundwater and runoff patterns. If not properly accounted for this can actually jeopardize the integrity of a road in the long term and can even result in a greater chance of landslides if the road displaces large amounts of water. Highways also have to be built in places and ways that minimize the amount of noise pollution they contribute to the surrounding area.
To achieve these ends highway engineers can use a variety of tools such as sound barriers or simply moving the planned route away from residential areas. This can be difficult; however, considering residential areas will still need to have easy access to the new highways.
When mulling over the data that’s been collected the people planning new highways will not only need to account for current usage but will also use forecasting to try and predict what the traffic will be like in the future. This is essential if the town or state constructing the roads doesn’t want to have to have them redesigned and rebuilt every 5 years because new traffic volumes make the existing roads obsolete. The process of forecasting future traffic levels and patterns begins with currently available data. This data is usually collected from a mixture of GPS data, traffic cameras and sensors, as well as studies that are regularly performed by traffic administrations. This current data is paired with other known information such as population data. All of this information is then used to develop what is called a traffic demand model, which is similar to demand models in economics. This model can help the engineers understand how much a given group of people in a certain area actually use the roads.
Future projections are then made regarding changes in population, vehicle ownership, job locations, and other variables. These variables are then punched into the demand model, which can begin to give the engineers a rough idea of how much traffic the area will be looking at in 10 years, 20 years, and sometimes even more. These projections usually do not need to go much further than 30 years, however, as most road surfaces have a useable life of about 30 years and will need to be replaced at that point regardless of traffic demands. This forecasting phase is extremely important in the planning of a new highway as designing roads around the current traffic flow would result in roads becoming restrictive and congested within just a few years, whereas a well forecasted and planned highway will last for decades.