When you need to move vehicles through a junction there are four main options:
- Give way/stop signs
- Traffic lights
- Roundabout plus traffic lights
Advantages of give way/stop signs
They don’t require anything other that road paint, a sign and sight lines to be maintained (e.g. hedges clipped).
They work well on quieter roads.
Disadvantages of give way/stop signs
They are less safe than traffic lights as they tend to increase the risk of t-bone (side impact) accidents.
In heavy traffic, vehicles emerging right from a side road can struggle to get across the traffic safely.
Crossroads provide a bigger challenge for drivers in low light and the signage sometimes get missed. This increases the risk of accidents.
Advantages of traffic lights
Traffic lights provide much more control to separate streams of traffic, reducing the likelihood of side-impact crashes.
They don’t take up much real estate – just poles or gantries.
Traffic lights can have phases to enable pedestrians to cross.
Traffic lights can have an area for cyclists to congregate at the front of the queue to allow them through first.
The timing of traffic lights can be customised to suit traffic flow at different times of the day, either using a computer or sensors.
Where there is a predominance of traffic in one direction, traffic lights can allow people to enter a heavy stream of traffic from a side road.
Traffic lights work well at complex junctions as the traffic that is allowed through has clear indication about where it is going.
Traffic lights are more efficient than roundabouts in heavy traffic because the long green phases allows vehicles to get up to speed, whereas on roundabouts, each vehicle approaches the roundabout at low speed.
Traffic lights with left filter lanes that have a give way sign are even more efficient.
Traffic lights work well in highly urbanised areas where sight lines are impeded by buildings.
Disadvantages of traffic lights
They require some installation on the road surface if induction loops are used to detect traffic.
They require some maintenance, and if they malfunction, it can cause significant traffic disruption.
Drivers running red lights can cause crashes.
Traffic lights that do not have sensors frustrate motorists who have to wait while.
Some types of vehicles don’t trigger the induction loop, e.g. some mopeds, cyclists – these people can be left stranded at a red light.
Advantages of roundabouts
Roundabouts work well to interrupt traffic in residential streets, helping to keep speeds down while giving equal priority within a junction to all traffic entering.
Where sight lines are open and the road is not busy, roundabouts maintain excellent traffic throughput.
Roundabouts with a free left turn are more efficient than a regular roundabout.
They can’t break like traffic lights can.
Traffic crashes between vehicles are overall less severe due to roundabout entrance speeds being lower.
Disadvantages of roundabouts
With the exception of mini-roundabouts, they cost much more than traffic lights to construct because of the requirements for the central part of the roundabout and the drainage.
Roundabouts take up more space than traffic lights due to the requirements of the central turning circle.
Roundabouts with a central reservation have ongoing maintenance costs for plantings.
Many drivers don’t understand how to indicate correctly on roundabouts.
Roundabouts pose challenges for cyclists, horse riders and pedestrians. There’s an increased risk of being involved in an accident for cyclists.
In heavy traffic, vehicles can back up around the roundabout, blocking the entrances and exits for other road users.
Drivers coming up to traffic lights can see the red or green light. In low visibility, and where the signage is in the foliage, it can be more difficult to see.
Roundabouts at the end of high-speed roads can come up on drivers very quickly, leading to late braking and an increase in accident risk; the design of approach lanes to these roundabouts needs to be considered more carefully.
Advantages of a roundabout with traffic lights
In heavy traffic, vehicles can be metered into the roundabout to avoid exits being blocked.
It can be safer for cyclists.
Disadvantages of a roundabout with traffic lights
It has the combined disadvantages of both roundabouts and traffic lights in terms of construction and maintenance.