On Britain’s motorways and dual carriageways, few driving behaviours generate as much confusion as undertaking. With traffic volumes increasing and lane discipline often inconsistent, drivers regularly encounter situations where passing on the left seems unavoidable. Understanding how undertaking fits within UK road rules is essential for staying safe, avoiding penalties, and maintaining smooth traffic flow.
What undertaking means in the UK
Undertaking occurs when a driver passes another vehicle on its left-hand side instead of overtaking on the right. Because vehicles in the UK drive on the left, the Highway Code establishes overtaking on the right as the standard and safest practice. This convention ensures that drivers know where to expect faster-moving traffic, reducing surprise and the likelihood of collisions.
While the term “undertaking” is commonly used, it does not appear as a specific offence in law. Instead, it is treated as a behaviour that may or may not be acceptable depending on circumstances. The legality of passing on the left is judged on whether the manoeuvre is safe, reasonable, and appropriate for the traffic conditions.
When passing on the left is allowed
The most widely accepted situation for passing on the left is during congested or slow-moving traffic. When queues form and lanes are moving at different speeds, drivers are permitted to remain in their chosen lane even if it happens to move faster than lanes to the right. In this context, passing vehicles on the right is considered a normal part of traffic flow rather than deliberate undertaking.
Another common scenario involves drivers who remain in the middle or right-hand lane without overtaking, often referred to as lane hogging. The Highway Code advises drivers to keep left unless overtaking, but not everyone follows this rule. If a driver in the left lane continues at a steady speed and passes a slower vehicle to the right without changing lanes, this may be lawful. However, it still carries risk, especially if the other driver suddenly decides to move left.
When undertaking becomes risky or unacceptable
Problems arise when a driver intentionally changes lanes to pass on the left at speed while traffic is flowing normally. This behaviour can be interpreted as careless or aggressive driving, particularly if it forces other drivers to brake or adjust their position suddenly.
Undertaking is especially hazardous near large vehicles such as lorries and buses. These vehicles have significant blind spots on the left-hand side, making it far less likely that the driver will see a car approaching from that direction. A moment of misjudgement in these situations can lead to serious collisions.
Because most drivers expect overtaking traffic to appear on the right, an unexpected vehicle passing on the left can cause confusion and delayed reactions. For this reason, police may intervene if an undertaking manoeuvre is deemed unsafe, even if no accident occurs.
Penalties and the importance of judgement
There is no fixed penalty labelled specifically for undertaking. Instead, enforcement usually falls under careless or dangerous driving laws. If a driver’s actions are considered to fall below the expected standard of driving, penalties may include fines, penalty points, or in severe cases, prosecution.
Ultimately, the rules around undertaking in the UK rely heavily on driver judgement. While passing on the left is sometimes unavoidable and occasionally legal, it should never be used as a shortcut to bypass traffic or express impatience. Good lane discipline, awareness of blind spots, and anticipation of other drivers’ actions remain the best tools for avoiding danger.
By understanding when undertaking is permitted and when it crosses into risky territory, drivers can make informed decisions that promote safety and reduce stress on increasingly busy roads.
