What is undertaking? In simple terms undertaking is passing another vehicle on the left hand side. It is not strictly illegal but I’m sure you can appreciate it is a dangerous manoeuvre as other drivers will not be expecting it and may be moving back into the driving lane. We are taught that where more than one lane exists on each side of the road, the first lane (far left, kerb side) is the driving lane and any extra lane to the right of this lane are overtaking lanes. We are also taught to move into the right hand lane to overtake a vehicle travelling slower than us in the driving lane.
The Highway Code actually states “do not overtake on the left or move to a lane on your left to overtake.” However, there are exceptions that apply when a car undertakes in slow-moving traffic if its lane is moving faster than a lane on the right, undertaking in this circumstance is often deemed safer than weaving in and out of traffic.
Undertaking however, is very common and usually due to ignorance of the Highway Code itself. Drivers very often don’t know they should not do it especially where other drivers are ‘hogging’ the overtaking lane. These lane hogging drivers may also be unaware that lane 1 is called the driving lane. They avoid it simply because they keep having to overtake so moving left and right in and out of the driving lane is tedious, requires lots of observations, judgement and use of mirrors so rather than changing lanes they hog the overtaking lane. Because they find mirror use tedious they don’t see you speeding up behind them and consequently don’t pull into the driving lane to let you pass.
It’s frustrating for sure and impatient drivers may perform an undertake with some aggressive gesturing as they pass but in actual fact it is them making the dangerous move. If they undertake inappropriately, they could receive a fixed penalty notice (FPN) for careless driving or driving without due care and attention. This could possibly result in 3 points on their license and a £100 fine if it is a minor offence, further sanctions could be imposed depending on the extent of the offence.
Surely when your changing lanes you need to be checking mirrors, blind spots and signalling so how is it dangerous to undertake? Well technically speaking it’s not entirely necessary to indicate to move back into the driving lane because that is what is expected of you once you’ve overtaken somebody. But….with so many drivers not adhering to this procedure there are times when you undertaking is not an expected and the car in front may have been distracted by something before moving back over. If they then realise their mistake and move back at the point you have decided to undertake then it is not standard practice and it can take other road users by surprise and therefore cause sudden swerving and distraction.
So my advice is to move back into the driving lane as soon as you have overtaken unless you are gaining on the next vehicle in the driving lane (within reason, gaining on someone who is 2 miles ahead doesn’t count lol). If you are the one feeling the need to undertake then do it with extreme caution. Take good all round observations and proceed slowly as the other driver may not check their mirrors before pulling back in. Use any previous experience and judgement you have to decide whether this is a good idea or not.