What Is Undertaking?

Undertaking is the act of passing a slower-moving vehicle on the left hand side or an inside lane, depending on the type of road you are travelling on. As you're supposed to overtake on the right, an undertake carries a significantly higher risk to both pedestrians and unsuspecting drivers.

Why Do People Undertake?

The most common instance of undertaking is on the motorway due to the frustration caused by middle-lane hogging, though you may also see undertaking performed by impatient motorists on dual carriageways or even more dangerously, residential streets. Some instances of overtaking are perfectly acceptable, such as undertaking if the vehicle in front of you is signalling to turn right, but undertaking is mostly synonymous with road rage or impatience.

What Does The Highway Code Say About Undertaking?

This is split in to two separate categories in the Highway Code, varying on the type of road that you are using.

Using the Road (Rules 159 to 203)

The highway code states two exceptions for undertaking on standard roads:


  • Rule 163 states "only overtake on the left if the vehicle in front is signalling to turn right, and there is room to do so."
  • Rule 163 states "stay in your lane if traffic is moving slowly in queues. If the queue on your right is moving more slowly than you are, you may pass on the left."

You can read this section of the Highway Code here.

Motorways (Rules 253 to 273)

As for motorways, there are two rules:


  • Rule 267 states that you should "Overtake only on the right."
  • Rule 268 states "Do not overtake on the left or move to a lane on your left to overtake. In congested conditions, where adjacent lanes of traffic are moving at similar speeds, traffic in left-hand lanes may sometimes be moving faster than traffic to the right. In these conditions you may keep up with the traffic in your lane even if this means passing traffic in the lane to your right. Do not weave in and out of lanes to overtake."

You can read this section of the Highway Code here.

Is Undertaking Illegal In The UK?

Whilst the Highway Code instructs motorists not to undertake, you do have to pay close attention to the wording. Whenever the Highway Code refers to something legislative, the wording "must" and "must not" is used to indicate that you are legally obligated to follow a particular rule.

Looking at the rules stated above, the wording "Do not" is used to describe the act of undertaking, which indicates that undertaking in itself is not illegal, but that doesn't mean that performing an undertake cannot contribute to a prosecution for an offence such as dangerous driving or driving without due care and attention, so in a round-about way, undertaking is technically illegal.

Can Cyclists Undertake?

It's rare that a cyclist would undertake a moving vehicle whilst both are travelling at speed, however when a cyclist passes a vehicle, this is described as filtering. Ideally, filtering is only done when traffic is stopped, otherwise it's generally advised that they overtake cars on the right, but cyclists are hesitant to do this due to the increased risk in manoeuvring. Another hazard cyclists must be wary of when undertaking / filtering is being crushed by HGVs, which typically happens when setting off after a traffic light change.

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