Roundabout Construction

Roundabouts are a common feature of our road networks here in the UK and provide a distinct advantage over traditional traffic signal-controlled junctions.

Roundabouts, in their most basic form, can be traced back to the early 20th century. The UK, being a pioneer in this area, saw its first circular traffic flow system introduced in Letchworth Garden City in 1909. However, the term “roundabout” wasn’t coined until the 1920s. These early iterations were substantially different from modern designs, with vehicles given the right-of-way when entering the circle, contrary to current rules.

The contemporary roundabout, with vehicles giving way to cars on the roundabout, originated in the UK during the 1960s. The design was modified based on studies by the Transport Research Laboratory (TRL), aiming to improve safety and efficiency. Since then, the roundabout’s popularity has grown worldwide.

Why Roundabouts Are Used?

One of the primary reasons for the adoption of roundabouts is the enhancement of road safety. Vehicles move in the same direction, which substantially reduces the potential for head-on and high-speed collisions.

Roundabouts often improve traffic flow, especially during off-peak hours, by allowing continuous movement without the stop-and-start nature of traffic lights. The smooth flow of traffic means fewer stops and starts, leading to reduced vehicle emissions.

In the long run, roundabouts can be more cost-effective than signal-controlled intersections, with lower maintenance costs and fewer delays.

Do Roundabouts Improve Safety?

Multiple studies suggest that roundabouts indeed enhance road safety. A study by the Insurance Institute for Highway Safety (IIHS) in the US found that roundabouts reduced fatal crashes by 90%, crashes with injuries by 76%, and all crashes by nearly 40%. The design inherently reduces the number of conflict points, and by ensuring that all vehicles travel in the same direction, the potential for severe crashes is significantly diminished.

Roundabout Construction

Constructing a roundabout in the UK involves a systematic process that is overseen by our civil and traffic engineers. This process ensures that the roundabout is not only effective in managing traffic but also safe for all road users. Here’s a simplified overview of the process we use in constructing a new roundabout:

Before any construction can begin, our highway engineers must select an appropriate site for the roundabout and survey the area. This involves traffic studies to understand the volume and type of vehicles that will use it. Additionally, a topographic survey is done to get a detailed understanding of the site’s topography, drainage patterns, and any potential obstacles.

Design Phase

Our Engineers use traffic volume data to determine the appropriate size and capacity of the roundabout. The size of the roundabout needs to be in line with expected traffic volumes. A small roundabout in a high-traffic area may lead to congestion, while an unnecessarily large roundabout can be a waste of resources and land.

We look at the local Geometry and angles of approach. This includes the design of the central island, the width of the lanes, the entry and exit angles, and the placement of pedestrian and cyclist paths. Proper sight lines must be ensured for drivers approaching and within the roundabout at every point.

Our Landscaping engineers make considerations are made for the central island’s dimensions, ensuring that it does not obstruct visibility. Proper signs and road markings are also designed to guide drivers, cyclists, and pedestrians before they commute across the new roundabout.

Site Investigations

Before breaking ground, a thorough investigation of the site’s soil and ground conditions is conducted. This helps our engineers decide on the appropriate construction methods and materials.

Checks are also made for underground utilities like water, gas, electricity, and communication lines. Relocation might be necessary if they interfere with the proposed construction.

Roundabout Groundworks

The road construction follows a usual build with the top layer of soil removed, this is graded to achieve the desired elevation and slopes for effective drainage.

Layers of crushed stone and other materials are then laid to provide a strong foundation and sub-base for the road surface. This base is compacted and sometimes bound with a binder to ensure durability.

Proper drainage systems, including culverts and ditches, are integrated to manage water run-off and the final layer, typically asphalt or concrete, is laid on top of the base. This provides a smooth driving surface for vehicles. Efficient drainage systems are crucial, especially in the UK, to prevent waterlogging and potential ice hazards in colder months.

Once the surfacing is done, road markings are painted, and signs are installed as per the design.

The central island and surrounding areas are also landscaped. Trees, shrubs, or sculptures might be added, but care is taken to ensure they don’t obstruct drivers’ visibility.

Safety Checks

Before opening to the public, safety audits are conducted to identify potential hazards and rectify them. Once all safety checks are complete, the roundabout is officially opened to the public.

It’s worth noting that the entire process, from site selection to opening, is subject to rigorous standards and guidelines set by UK authorities, ensuring the safety and effectiveness of the roundabout.

The UK has specific guidelines and best practices for roundabout construction. We are well acquainted with these to ensure compliance.

If you have a new project in the pipeline or need a quote on a new roundabout or alterations to an existing roundabout, contact us today for a quick response and quote.