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Filtering - what's legal and how to do it

This is another tip I've completely rewritten for 2019, because filtering past or through slow-moving or stationary traffic is one of the most hotly-debated topics in biking. Please note that this article refers ONLY to UK practice. Whilst other nations have legalised filtering (Belgium for example) and lane splitting is legal in California (which has produced a code), it's up to you to determine what the law is if you're not a UK reader. And don't forget to reverse left and right if you ride on the wrong side of the road.

So, here in the UK Motorcycle Roadcraft explains that filtering is a form of overtaking to make progress past stationary or slow moving traffic but gives no real advice on where or where not to do it. Filtering and other road users' response to filtering motorcycles is also laid out in the Highway Code, which says in the section about 'Road users requiring extra care' that:

"It is often difficult to see motorcyclists and cyclists, especially when they are coming up from behind, coming out of junctions, overtaking you or filtering through traffic. Always look out for them before you emerge from a junction; they could be approaching faster than you think. When turning right across a line of slow-moving or stationary traffic, look out for cyclists or motorcyclists on the inside of the traffic you are crossing. Be especially careful when turning, and when changing direction or lane. Be sure to check mirrors and blind spots carefully."

There is also guidance on the Highway Code which refer to overtaking, but can be applied by extention to filtering. Let's mention the places you must not overtake first.

You may not:

  • cross solid white lines except to pass an obstruction or to overtake a slow (10mph), horse, bicycle, local authority vehicle (with its amber beacon flashing)
  • overtake after passing a No Overtaking sign, until you reach the end of restriction sign
  • overtake the vehicle nearest a pedestrian crossing

However, you may overtake vehicles where there is a solid white line on your side of the road if you can pass the vehicle without crossing or straddling the white line with any part of your vehicle.

You may:

  • enter a hatched lane divide as long as it has dashed boundary lines and it is safe and necessary to do so
  • pass traffic on the left (ie undertake) queuing or slow moving traffic but you should not change lane in order to gain an advantage
  • pass traffic on the left if the vehicle is indicating to turn right
  • pass traffic on the left if you are turning left in a dedicated left turn lane
  • pass traffic on the left in a one way street

So whilst there are some places we must NOT filter, there are no clear legal guidelines about HOW to filter. Unfortunately, some years back a wholly inaccurate article on filtering claimed to explain the law. As is the way of the internet, search engines turn it up from time to time, whereupon it's 'rediscovered'. I'm not going to tell you were to find it because it's inaccurate but I will tell you why you shouldn't trust it.

The article's starting point was that a filtering crash should always be the driver's fault. Commenting on a case, probably Leeson vs. Bevis Transport (1972), where the motorcyclist was found equally responsible for a collision with a van driver emerging from a side road, the article was penned in a way that implied that a filtering collision was always the other driver's fault:

"I mean, you're filtering past stationary cars and some clown t-bones you and you have to pick up half the bill?""

The Survival Skills approach is always to look at why things go wrong on the road, and I always encourage riders to see a situation from the other road user's perspective. We could easily rewrite that statement:

"I'm trying to pull out of a side-turning into a busy street with parked vehicles on either side making it almost impossible to see, and some clown filtering past the bus that has kindly let me out t-bones me and I have to pick up half the bill?"

But it got worse. The writer then claimed that the law on filtering 'changed' after a case was heard in the Court of Appeal in 2006. The writer said:

"...in the case of Davis vs Schrogin, the judge found that "a filtering motorcyclist passing stationary or very slow moving traffic could not be to blame if a collision occurred if the rider had no chance to take avoiding action", then jumped to the conclusion: "Ladies and Gentlemen, filtering past stationary traffic is no longer a grey area - it's completely legal".

First of all there was no 'change in the law' for the very simple reason that there was - and never has been - any road traffic law that defines filtering or how to go about it.

You may be wondering how do courts make a judgement on a filtering crash? The answer is based partly in terms of how each road user behaved. The question asked is "did the rider or drive behave in a way that that a competent driver or rider could be reasonably expected to drive or ride?"

Where it gets complicated is that a previous judgement ('precedent') by a magistrate's court, crown court and county court is not binding. Although judges will look at previous decisions if the case is sufficiently similar, each case will be judged on its merits. However, higher court judgments (except in the House of Lords, where the Lords can change their minds) including those from the Court of Appeal, are binding on themselves and lower courts, UNLESS it can be shown that a new case has enough differences that it should be decided on its own facts. In that case, the judge can distinguish it from the previous case by pointing out the relevant differences and thus not be bound by precedent.

So the second error is to argue that a judgement in a single court case defines how other cases might turn out. Whilst case law sets a precedent, that precedent only applies in identical circumstances and the assessment of each individual case will depend heavily on statements and witnesses. There's no 'law making it legal'.

In any case, being on the right side of insurance claim doesn't mean much if being in the legal 'right' doesn't stop us being carted off in a pine box! So, let's move on to looking at filtering from a practical perspective.

Above all, we need to be aware of where we might need to stop suddenly. What we mustn't do is treat empty road ahead of us as a 'motorcycle lane' whether we're filtering down the outside of a queue of traffic against oncoming vehicles, or (to use the American term) 'lane splitting' between queues moving in the same direction.

And that determines our speed. We have to be able to stop in the distance that we can see is clear AND EXPECT TO REMAIN CLEAR. So what's the 'right' speed? Well, it's all down to the physics of stopping. Two issues. The first is 'double your speed, quadruple your stopping distance'. The second is 'three-quarters of your braking distance loses one-quarter of your speed'.

In the collision between Messrs Schrogin and Davis, Mr Schrogin was stopped in a traffic jam in his car on a straight road, whilst Mr Davis was overtaking the stationary queue on his motorcycle. As nothing was coming in the opposite direction, Mr Schrogin decided to execute a U-turn and failed to see the approaching bike. Mr Schrogin accepted that he had looked the wrong way but argued that Mr Davis was contributory negligent. Mr Davis admitted seeing Mr Schrogin's car moving towards the kerb in preparation for the U-turn but claimed that as he was no more than five cars' length back from the point of impact, he had no chance to stop.

What surprises me is that when the case went to the Court of Appeal, it held that Mr Davis was so close to the point of impact that he could not have avoided the collision, so there was no basis for a finding of contributory negligence. But could the rider have stopped, given the quoted five car lengths?

Let's do a quick sum. Something like a Vauxhall Astra is around 4.5 metres long, and that's a fairly average sized car. Multiply that by 5 and you get 22.5 metres. Add a metre gap between the five vehicles and we probably have at least 25 metres in which to stop. When I demonstrate emergency stops, I can bring the bike to a standstill on a reasonable surface in the dry in around 10 metres from 30mph. So could a competent rider be 'reasonably expected' to stop too? if Mr Davis was accurate in his memory of distance (and post-crash, most witnesses are hopelessly inaccurate) then I'd say "yes, a competent rider could be reasonably expected to stop"...

...if he wasn't taken completely by surprise by the event! If you've read Keith Code's 'Twist of the Wrist' books, you'll know all about 'Survival Reactions', the unplanned response to emergencies. They're triggered by SURPRISE!, something you can find out more about by looking up our 'No Suprise? No Accident' campaign. If we're not predicting something to happen, then SURPRISE! kicks in and triggers the Survival Reactions, which include freezing and ineffective braking. So the problem is really our expectations about that happens next. Is it really unexpected if a pedestrian steps out from between two vehicles? Or a door opens into our path? Or a car swaps lanes? Or a van pulls out of a side turning. Or a car starts to make a U-turn. Of course not. At least, not if we're planning for the Worst Case Scenario, rather than looking at the empty tarmac as a motorcycle lane.

If we can see what's happening ahead - a car edging the left in a queue is a great clue that the next movement will be the driver swinging out to perform a U-turn, whilst a gap being left between two vehicles is an equally fine clue that someone's leaving space for an emerging vehicle or for someone to cross the road - we just have to interpret what we see. But the moment our view ahead is restricted - perhaps by a bus - then we have to assume that whe might have to stop level with the front of that vehicle - and down comes the speed.

You may read that so long as you keep to a 15 mph speed differential with the vehicles you're filtering past, you'll be safe. I know where that claim came from, and what they ignored was the physics. If we're filtering past stationary traffic at 15 mph, our stopping distance is about a metre. If we're filtering past traffic moving at 10 mph at 25 mph, our stopping distance is about six metres. By the time our speed climbs to 55 mph, filtering past traffic moving at 40 mph, our stopping distance is out to 35 metres or so. That's a huge distance back from where things can go wrong. It's already too late to worry about the cars we're passing NOW.

Now, if you take a look at the shape of a braking graph, it takes us around half the total stopping distance to lose (very, very roughly) one-fifth of our speed. And we lose approximately three-quarters of our speed in the final quarter of the available braking distance. The result is that if we can't stop, impacts are MUCH harder than riders intuitively expect. We only need to run out of space by one-quarter of the distance, but we hit with three-quarters of the impact of not braking at all. And the higher our starting speed, the worse the impact. Only considering traffic speed differentials is a really nasty filtering trap. Once traffic is moving at around 20, I'll be back in the traffic stream. You certainly won't see me lane splitting at motorway speeds.

What other tips can I give you?

Most important of all, assume you will NOT BE SEEN. Don't expect to be seen in a mirror. Just like you, drivers are watching the traffic ahead when it's moving in queues, so that they don't run into the back of a vehicle that stops suddenly. Mirror use is erratic at best, the view is often blocked by the next vehicle back, and as soon as there is the slightest curve in the road, the mirror won't show a filtering motorcycle until the last second in any case. All the hi-vis kit in the world, even riding with lights on main beam - makes no odds if the bike's not visible. And loud pipes? When I'm driving, it's not uncommon that the first time I hear them is when the bike is alongside. They project the engine sound backwards, not forwards. They do not save lives. So we need to look forwards and be ready to change our plans and even take evasive action. And keep a thumb near the horn - it might just stop a driver moving into your path.

When passing stationary traffic on a single carriageway road, where possible move into the opposite carriageway and stay wide - it gives us a better view of emerging and U-turning vehicles. But don't be tempted to carry too much speed - as we've seen, it may be necessary to stop suddenly so watch out for junctions, where pedestrians might cross and only filter past after checking it's clear. Don't be tempted to go the wrong side of a solid line on your side of the road or Keep Left islands, it's an offence and a guaranteed nick if you're spotted. When confronted with oncoming traffic it's still possible to filter IF there is sufficient margin, but as we get closer to the vehicles we're filtering past the speed must come down - could we stop if a door opened? Eventually, when further progress cannot be safely made, we should find a space and move back into the queue. Don't forget we should never force another vehicle to swerve or slow down - this could count as grounds for a prosecution.

What about filtering on the left? First of all, there is no offence of 'undertaking' if you pass the left of slower traffic on single carriageway roads, dual carriageways or motorways. But... like all filtering or lane splitting, if done in a way that inconveniences other road users, specifically forcing them to change speed or direction to avoid us, it can be construed as careless or even dangerous driving, offences which carry points, a fine and even a custodial sentence if dangerous enough.

Legal or not, fltering to the left of a queue is generally riskier for several reasons. The first is because - bar the odd foreign vehicle - the driver is sitting on the far side of the vehicle and is much less likely to see a bike coming up in the passenger side mirror. Keep a good eye out for side turnings and entrances, and watch for vehicles turning left into it. We're also at risk from oncoming vehicles turning right through stationary or slow-moving queues because we're blindsided by the vehicles we're passing. And don't forget emerging vehicles too - drivers often miss spotting cyclists as well as bikes filtering alongside the pavement because they're busy looking at the queue of traffic and working out whether someone will let them out. Although some bus lane allow motorcycle access at any time and it's perfectly legal to use them when not in use - check the sign boards at the beginning of the lane - we're now passing slower traffic to our right and the same problems apply. It's not difficult, if there's a turning to be see or a gap to the right, then look for - and respond to - the turning vehicle. Slow right down, expect NOT to be seen and be prepared to Give Way.

When lane splitting on any dual carriageway including a motorway, we're always passing to the left of a stream of traffic, so the same mirror issues appear. Where there are three lanes, passing between lane two and lane three (the right-hand lane) is usually the best bet. HGVs are not allowed to use the outside lane so there's a bit more space, a slightly better view, and you won't be lane-splitting between two trucks too often. As a rule of thumb, look ahead for gaps in each lane big enough for a vehicle to move into - if there's a space, someone will aim to take it, and it's usually the driver on our RIGHT who, because they are usually moving to a slower-moving lane - is least likely to see us approaching in the passenger side mirror. Be particularly careful when lanes move at different speeds. It's called 'lane shear' and drivers will do exactly what we're doing - try to get to the faster lane to make progress. Be ready for lane swapping to the faster-moving lane. Watch out too near junctions and services. Drivers will generally move left through the lanes to get to an off-ramp, and after we pass the on-ramp, they'll be moving to the right. And don't forget, there are junctions where drivers can turn right across a dual carriageway.

Plan as far ahead as possible. Be particularly cautious passing long vehicles. The driver's view from the cab is often not very good, they need space to turn on bends and at junctions and may swing wide, so hang back till you know what they are doing, and pass when they've straightened up. Watch out for buses parked at an angle in a bus stop - if you can't see the mirror, the driver can't see you. Make sure you spot left or right turn lanes so you can anticipate turning vehicles. Look for obstructions like traffic islands and bollards, pinchpoints either side of the road, or cyclists - they will all make vehicles change position and possibly 'squeeze' our space. Watch the surface for cats-eyes and painted lines, potholes or slippery surfaces which could make braking or steering difficult. Look for lane markings approaching junctions to predict traffic movements, and watch traffic lights to judge the sequence - we may be able to slip to the front whilst they are red, but we may need to look to slip into a gap in the queue so we don't get stuck against the island when they turn green.

Watch out for legal traps too. Just because you see lots of other riders breaking laws, don't imagine they all get away with it. Don't get caught out by cycle lanes bounded by a solid line, and be aware that we're not supposed to use the advanced cycle stop box at lights. In practice, nearly everyone on a bike uses them, but riders do get nicked - some are monitored by CCTV. Likewise active bus lanes are often monitored too. Passing in a zone marked with a broken line and cross hatching is allowable if "safe and necessary", but it's illegal to enter a zone with chevrons and a solid line. Be careful about moving back and forth to the fastest moving lane on a multilane road to make progress in heavy traffic. A traffic cop told me that he was shown a video of a motorcyclist moving at speed from lane to lane on a busy motorway on a training course, and was asked for comments. He thought that the rider was safe enough, although a little closer to some of the cars than he'd like, but that generally he had no problem with what he saw. So he was surprised that the video evidence had been used to prosecute the rider, who'd be found guilty of dangerous driving and handed a ban!

Try to be courteous to other road users, even the ones holding you up. Don't harass them with rev bombs or drive a centimetre behind with lights on stun. Even if your impatient bahaviour doesn't trigger an equally aggressive response, it can distract them into making a mistake that puts you at greater risk. Give drivers a chance to see you - a highly-manoeuvrable bike can cut through traffic and really DOES appear from nowhere. Back when I was a courier, the best despatch riders used to move through traffic almost imperceptibly - but they were always there at the head of the queue. And if you're from a big city, don't try the same filtering techniques out in the sticks. What works on the Euston Road in London is asking for trouble in a small Scottish town.

If you are not confident you can do it, don't! And don't copy other riders if you're not sure what you're doing either. You've no guarantee they have a clue what they're doing. If there's one rule to follow, look for places it's easy to filter - wide roads, stationary traffic. Avoid it where it's tricky - narrow lanes, against heavy oncoming traffic. You might see someone else taking a risk, but a little caution, a little extra time on your journey will mean you arrive at your destination by bike rather than at hospital by air ambulance.

Taken cautiously, filtering can be relatively low risk and we can still make good progress by combining excellent observation with careful planning. I spent sixteen years as a courier, and covered half-a-million miles, so I must have filtered tens of thousands of miles through London, and the worst that happened was hitting a taxi driver's door when he opened it to empty his ashtray just as I was filtering past. His door caught my clutch lever, which broke one of my fingers. But as I point out in my Urban Survival Skills advanced motorcycle courses, filtering isn't 'safe'. It's one of the main killers of riders in big cities, usually because riders become complacent. Nothing ever went wrong before - but it only needs to go wrong once, and we're in the KSI stats.

Kevin Williams
Survival Skills Rider Training

...because it's a jungle out there


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What is Survival Skills all about?

How are Survival Skills Courses put together and taught?
The Making of a Good Instructor - musings on my Driver Education course

Would a National Standard for advanced training be appropriate?
Writing a riding tip - what detail is necessary?
What to do if you've had an accident
Accident Statistics - dispelling some myths

Improver or advanced, pragmatism or perfection?
Piling on the miles
Compartmentalisation & Practice -  the key to learning new skills
Countersteering - Question and Answer

Braking Rules and Tips
Over-confidence and Riding at the Limit
Practice makes Perfect
The Danger of Misunderstanding
Learning from your Mistakes
A Moment of Inattention
Staying Warm
Staying Awake
Don't just ride for yourself, ride for others
Filtering - what's legal and how to do it
Cornering Problems 1 - Lean or Brake?
Springing into Summer - polishing off the winter rust
Group Riding - Rules and Tips
Awareness of Risk and Risk Management
Cornering Problems 4 - Stability and the "Point and Squirt" technique
Cornering Problems 3 - Staying out of trouble! Pro-active Braking or Acceleration Sense?
Cornering Problems 2 - Staying out of trouble
What is Risk?
Avoiding Diesel
The Vanishing Point - is it enough?
Posture - the key to smoother riding
When the Two Second Rule is not enough
Riding in the Dark
Roundabouts - straight lines, stability and safety
Slow Speed Control
Aquaplaning - what it is and how to deal with it
Rear Observation - when to & when not to!
Staying upright on icy roads
KISS - 'Keep it simple, Stupid' or Low Effort Biking
Overtaking Safety - avoiding vehicles turning right
Proactive versus Reactive Riding
Living with  Lifesavers
Which Foot? The Hendon Shuffle - Question and Answer
Carrying a passenger - Question and Answer
Riding in the rain
Riding in strong winds
Sorry Mate, I didn't see you - an analysis of SMIDSY accidents
Ever gone into a corner too hot and had it tighten up on you?
The Point & Squirt approach to corners
A time to live...
Target Fixation - Question and Answer
The Lurker, the Drifter and the Trimmer
The five most important things I learned as a courier
Overtaking - Questions and Answers
Precision riding - or keeping it simple?
Wide lines, tight lines, right lines - the law of Diminishing Returns
Surface Attraction
Euphoria - when your riding is just too good to be true
Straight line -vs- trail braking
Sit back, close your eyes, relax... and hope for the best
Before you overtake, do you...?
Do you need to blip the throttle on a downshift?
Holiday Riding Tips 1 - Dealing with hairpins (a new occasional series)
Holiday Riding Tips 2 - The (drive on the) Right Stuff
Why SMIDSYs happen
Avoiding dehydration - riding in hot weather
Riding errors - and avoiding them
Season of mists and mellow fruitfulness - riding in fog
Where does Point and Squirt come from?
Overtaking - lifesavers and following distances
Offsiding - what is it, and why you should think before you do it!
Anger Management - dealing with "red mist" and "road rage"
That indefinable gloss
Overtaking on left-handers - experts only or best avoided?
Apex or Exit - what's important when cornering?

Developing 'Spidy Sense'

Armchair Riding - how to improve summer skills in winter

Working towards a BTEC in post-test instruction part 1

Working towards a BTEC in post-test instruction part 2

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