Roundabout or traffic lights – which is best?
23 Jun 2025
As traffic volumes increase in line with our growing population, more of our road intersections require some sort of control to provide people with safe and timely passage through an area.
This usually means a roundabout or traffic lights. But is one system better than the other? Which system suits which conditions?
Every site is unique and needs individual consideration. The main drivers for traffic designers are to move traffic as safely and efficiently (maximising the number of vehicles getting through the intersection as quickly) as possible. Elements taken into consideration include the daily volume of traffic and how much of that traffic are heavy vehicles, whether there’s a dominant directional flow of traffic, the amount of space available and the elevation of the site (is it flat or sloping), and other transport modes using the intersection.
If the directional flow is relatively even on each arm of the intersection, then a roundabout might work. Where the traffic flow is more dominant from one direction, a roundabout will be less efficient because traffic at the less-dominant arm/s has to wait a long time for a gap in the traffic before it can enter the roundabout. Traffic lights work better in this situation because they’re timed to give all arms of the intersection turns. The dominant flow will likely have longer green-light time so more traffic can get through, but the quieter arms of traffic will also get a fair turn. Traffic lights are more versatile and the green light timings can be adapted either temporarily if demand changes during the day or an event causes extra traffic, or permanently if conditions change due to growth.
Roundabouts are usually not safe at intersections where there’s a significant number of cyclists and pedestrians, especially where there’s a high number of heavy vehicles. It’s not easy or safe for pedestrians to cross or cyclists to travel around roundabouts.
Roundabouts can be designed to cater for heavy vehicles. Heavy vehicles need enough turning space so the roundabout needs to be wide or designed so a truck can run over the top. Roundabouts built on sloping land can also be a challenge for heavy vehicles. If they enter a roundabout intersection too quickly, they can tip over. Roundabouts are sometimes considered a good way to reduce speed as gateways to slower traffic areas.
Traffic lights are often preferred in areas where there’s limited space and/or there are other intesections nearby.
Traffic lights
- Traffic from each arm of the flow gets a fair turn.
- Safer for pedestrians and cyclists.
- More efficient in high-speed areas.
- Priority can be altered for changing traffic conditions.
- Drivers have to wait their turn.
- More maintenance required, ie electronic equipment as well as the road surface.
Roundabout
- Keeps traffic moving if flow is balanced.
- Need less daily oversight.
- Crashes tend to be less severe due to the angle of impact (typically 450 rather than 900 at traffic lights)
- Some drivers have long waits at intersections with unbalanced flows.
- Needs more space and best in flat locations.