Section of the report I contributed to

 

1.1.1 Types of Roundabouts

a) Single Lane Roundabouts

As seen from figure 1, single lane roundabouts are the most standard type of roundabout design. The most common layout for this roundabout is two or more roads converging and only one lane around a center island. No traffic lights are typically found for this design, hence drivers use the ‘Mirrors-Signal-Manoeuver’ (MSM) routine to signal and inform other drivers of their exit. For example, when taking the first exit to the left, signal left when nearing the roundabout, however if the drivers plan to take a full circle, or exit on the right, signal right. This design can be expanded to multi-lane roundabouts to allow drivers to have more than one lane to decide their exit (Passmefast, nd). 

Figure 1

Single Lane Roundabout

Note. A typical single lane roundabout  design (Passmefast, nd)

When it comes to its benefits, a standard roundabout is able to reduce congestion, by improving efficiency during peak hours, therefore reducing any delays. With a decrease in delays during peak hours, drivers would have fewer stops and hard accelerations, meaning pollution and fuel usage would be reduced concurrently (U.S. Department of Transportation, 2022). 

Despite their benefits, single lane roundabouts have too many merge points, especially for multi-lane roundabouts, which could increase the risk of collisions. Additionally, with  drivers trying to ‘cut’ the roundabouts by going against the counterclockwise flow, it would put other drivers, pedestrians, and other road users at risk (bishoplegal, nd). 

b) Turbo Roundabouts

As seen from figure 2, it demonstrates that for turbo roundabouts, it comes in a formation of two lanes whereby the driver needs to pre plan their intended direction of exit. It is similar to the single lane/ multi-lane roundabouts but there is a significant difference, as once the travel route has been decided, the driver is ‘locked into’ their lane decision. Usually, one lane is designated for the first exit on the left, while the other lane exits at the far right (Passmefast, nd). 

Figure 2

Turbo roundabout

Note. Turbo roundabout design (Moore, 2020)

Turbo roundabouts have proven its effectiveness despite being a relatively new design that was implemented in the early 2000’s in the Netherlands. There are benefits when implementing the turbo roundabout. 

Firstly, fewer conflict points, with nested spiral lanes being introduced, it reduces lane changes at circulatory areas and forces vehicles to exit. Through lane markings and raised lane dividers the amount of conflict points reduces from 16 to 10 points, as seen in figure 3. 

Secondly, it lowers vehicle speeds, the turbo-roundabout channels vehicle movement to a narrower area than a regular multi-lane roundabout. In simpler terms, the average speed when driving on the multi-lane roundabout lowers when on the turbo roundabout. It was shown that traffic accidents were reduced by 72% when the turbo roundabout was implemented (turboroundabouts, nd). 

Figure 3

Conflict points at multilane and turbo roundabouts 

Note. Comparison of conflict points between multilanes and turbo roundabouts (turbo roundabouts, nd)

c) Access-Controlled Roundabouts

As shown in Figure 4, access-controlled roundabout’s designs are pretty straight forward; traffic lights are situated at the start of each roundabout entrance/exit to facilitate traffic flow. The rules are that when the light is green, drivers can proceed onto the roundabout, after which drivers are to follow the standard rules of multi-lane roundabouts (Passmefast, nd). 

Figure 4

Access- Controlled Roundabout

Note. Access controlled roundabouts, with traffic lights at the entrance/exit of roundabout (Passmefast, nd)

1.1.2 Mechanics Of Roundabouts

Additional features are implemented in order to reduce accidents from occurring on roundabouts. By implementing eco-luminance lighting and designing the geometric layout to fit the specific site requirements, it is able to improve safety of pedestrians or other road users.

a) Eco-luminance Lighting 

Firstly, improving road user’s visibility at roundabouts at night or bad weather through the usage of ecoluminance as seen in figure 5. The concept behind it consists of incorporating ‘light reflected from plants, low-height bollard based lighting, and retro reflective elements’, in simpler terms, using overhead LED lamps to naturally reflect off plants. Through this method, the lighting is able to enhance drivers visibility and increase awareness of pedestrians crossing the roads vice versa (Transport Research Synthesis, 2014). 

Figure 5

Ecoluminace lighting implemented at a roundabout 

 

Note: Ecoluminace lighting implemented at a roundabout  by the Lighting Research Centre (LRC) in United States (Transport Research Synthesis, 2014)

The lighting layout can be done in two ways, perimeter illumination and central illumination. For perimeter illumination, lighting is mostly focused on pedestrian and cyclist areas, providing good visual support on roads, making approach signs clearer for drivers to see at night. Central illumination focuses on improving perception of the roundabout from a distance. Compared to perimeter illumination, it requires less light poles and only makes exit signs clearer for drivers (Transport Research Synthesis, 2014).