Whether you’re embarking on the road trip of a lifetime or simply commuting between home and work, we seldom give much thought to how the roads and highways which make these journeys possible were designed in the first place. How did the engineers and construction teams responsible for building the roads we so depend on decide on the route, alignment and materials to be used?
We take a peek into some of the factors and challenges which need to be considered when designing a road, as well as some new initiatives and guidelines for making future roads safer and more sustainable.
Road design elements and considerations
Horizontal and vertical alignment
While the shortest distance between two points may be a straight line, in the real world factors like terrain, topography, soil type, steep slopes and obstacles which need to be navigated around all have to be considered when planning the route of a new road. Aside from the road itself, space also has to allocated for shoulders, curbs, emergency lanes and barriers.
Once a route has been decided, road designers need to be able to estimate the number of earthworks which will be required to level the route. To do this, engineers use computer modeling to produce a three-dimensional road alignment and cross-sectional profile.
Reaction and maneuver time
Whether it’s the crest of a hill or an obstacle on the inside of a curve, a road’s geometry and layout can affect the sight distance (visible length of road) of a driver. If there isn’t a sufficient amount of time for drivers to become aware of the situation up ahead, decide how to react and complete the necessary maneuver, accidents become more likely.
Refuge islands and access to public transport
Unless you’re designing a highway, consideration has to be made for how pedestrians and cyclists are going to cross the road, and where buses, taxis and other forms of public transport can leave and enter the flow of traffic. If the road is wide or has several lanes, refuge islands may also need to be included in the road design so pedestrians crossing only have to navigate one direction of traffic at a time.
Traffic type and density
The quantity and type of traffic expected to use the road is important at every stage of the design process. From how many and how wide lanes need to be, if and where turn-around points need to be in place, what the design speed should be, how much clearance is required for taller vehicles, to the optimal type of driving surface, road designers need as accurate and detailed information as possible.
Traffic counts along existing roads need to be made, bearing potential seasonal variations (such as a coastal holiday destination) in mind, and then forecast 10 to 20 years into the future. If a road project gets delayed, these figures need to be updated.
Other factors which need to be considered include drainage (roads will last much longer if they take advantage of well-drained terrain and bypass areas of poor drainage), the socioeconomic and environmental impacts of the new road, and the most appropriate road surface and wearing course material type – all balanced against the cost and budgetary constraints of the project.
Designing more sustainable roads
From the inclusion of EV charging lanes and smart parking lots, to road infrastructure which supports the collection and distribution of renewable energy, change is definitely afoot in the field of road design. As ever more electric and autonomous vehicles take to the streets, the opportunity to create safer, more sustainable roads has never been greater. But until these cutting-edge technologies gain traction, road sustainability still starts from the ground up.
One of the biggest factors affecting a road’s overall environmental footprint is its durability. Roads which require regular maintenance and repair have an ongoing environmental cost, but this can be mitigated by designing more durable and long-lasting roads – and that starts with adequate stabilization.
In regions with naturally soft soils, products such as geocells offer an attractive solution. Thanks to their ability to reduce costs and improve lifespan -while also providing a more sustainable alternative to conventional stabilization measures- geocells are an increasingly utilized road design technology in South Africa, Canada, Russia, Israel and Mexico. Aside from improved durability, geocells (or cellular confinement systems) also reduce the quantity of high-grade aggregate which needs to be hauled in, reducing the carbon footprint of the project.
By combining data-driven design and computer modeling with sustainable construction practices -all while preparing the way for smart technologies and electric and autonomous vehicles- there’s never been more potential in the field of road design.