Filtering is probably the 3^rd most commonly discussed subject during advanced rider training (after cornering and overtaking ).  Successful filtering through traffic is really about balancing risk with progress.  We need to determine where we can do it with the maximum gain and minimum risk and avoid filtering where the risk is high and the gain minimal.  As well as looking at the legal aspect of filtering it's also worth looking at how other road users regard filtering and also how your insurance company will view it in the event of establishing liability. 

What the law says about filtering

Contrary to the belief of some motorists, filtering is entirely legal in the UK, providing that it is done safely.  Typically once traffic speeds are high enough to suggest that the traffic is no longer queuing, the police may then regard your manoeuvre as a dangerous overtake. So for example on a Motorway a rider unlikely to draw police attention if they filter traffic doing a maximum of 20ish mph and they themselves don’t pass at much over that speed. 

Where is filtering illegal

Overtaking (or filtering) on the appraoch to a zigzagged crossing

You may not pass the lead vehicle on the approach to the crossing if it has stopped or is stopping to allow people to use the crossing.  You can pass all the cars behind the lead vehicle and you can pass the lead vehicle once it has passed the crossing.  You can also pass any vehicle that is queuing due to congestion further up and not as a result of the crossing.

There is also some confusion over the concept of a ‘technical’ infringement of the law, where legal precedent has stated that a road user shall not be guilty of an offence if it is technical and no other road user was endangered.  However, to the best of my knowledge the technical defence is only valid in examples where there are two or more approach lanes and the driver in lane 1 arrives before the driver in lane 2, but the driver in lane 2 leaves before the driver in lane 1.  This is classed as overtaking the lead vehicle, but is regarded as technical breech.

It’s worth noting that when passing vehicles queuing on a crossing due to congestion, its vital to exercise extreme caution and pass very slowly, as it’s highly likely that you will be unable to see any pedestrians who emerge between the vehicles to take advantage of the ‘stationery’ traffic.

Overtaking or filtering on solid white lines (no overtaking)

Here normal rules for overtaking apply.  If you can get passed without crossing the solid white line, then you can pass queuing traffic.  If the traffic is turning or meets the criteria for slow moving, you can pass.  Again, because you will need to filter in a very small space you need to exercise caution when doing this.  Typically (although not in all cases) the no overtaking lines are there because of a concealed hazard that you may not be able to see.  In addition they don’t normally last that long (although again some authorities do abuse them).  This should factor into you planning when deciding if it is safe to filter in a no overtaking area.

Filtering and insurance

It would be really nice if one of the big motorcycle insurance companies published details of how they will treat a claim when the rider is filtering.  However, at best the information is sketchy.  In general you will not succeed with any claim against a 3^rd party in any of the following situations:

B) Narrow Gap - You collide with a vehicle while filtering between a narrow gap of cars because the car driver has either obstructed you or moved over within the lane without looking.  As it is highly likely that you wont have any witnesses, you will find it difficult to prove that he hit you rather than the other way around.  You stand a little more chance of succeeding if you are in an adjacent lane when they move into your path.  Again you will need witnesses, so if you’ve just zoomed passed 50 cars at high speed, riding in an aggressive fashion, expect a queue of witnesses ready to stand against you.

Avoiding risk when filtering

As mentioned earlier in this article, successful, safe filtering is about balancing risk vs. progress.  There are a number of situations that its worth being aware of, where the risks we take far out way the benefit we gain.

The faster (or slower) we ride relative to the speed of other traffic, the greater risk we have of having an accidents.  In order to understand why our risk increases it worth looking at the statistical event that road safety experts know this as the 85^th percentile rule.  Those drivers and riders who choose to travel around the 85^th percentile of free flowing speed represent the group least likely to have an accident.  In simple terms travelling faster than the avg. speed, but slower than the top speed means we are less likely to have an accident.  There are decades of accident statistics to back this claim up, but why is it relevant to filtering?  The more our speed deviates from that of other road users, the greater the risk.  Filter much faster than the traffic and our risk of coming into conflict increases, as does the severity of that conflict.  By definition free flowing traffic will find it much easier to change lanes than queuing or slow moving traffic.  By keeping our filtering speed down and only filtering slow moving vehicles we reduce the risk of traffic changing lanes, reduce our risk of injury in the event of an accident and maximise our ability to take avoiding action.

It’s also worth noting the risk vs. reward: If we have a 10-mile traffic jam with traffic speeds averaging 10mph and choose a 30mph filtering speed.  We save 40 minutes (in 20 minutes) by filtering the traffic (not uncommon between J9 and 16 on the M25).  If we have traffic travelling at 45 mph and we choose to filter at 60mph.  We save 5 minutes every 5 minutes, while our risk of crashing increases massively.  In summary the slower the traffic we filter the greater the gain, the faster the traffic the greater the risk.

Not reducing speed as the traffic slows down

Our greatest risk of having an accident is at the beginning and end of the queue.  For example motorway or dual carriageway users will look to pick the shortest or fastest moving line at the beginning of the queue and will often not make proper rear observations as they dart between lanes.  As a motorcyclist the temptation is to gradually reduce our speed by rolling off the throttle as we slide between traffic at the start of the queue.  However, at this point our risk is greatest, so it is important to slow down with the traffic and only begin filtering once the lanes have settled.  If the queue is unexpected or slowing rapidly its worth keeping an eye on your mirror, in case a vehicle approaches at high speed and has not anticipated the slowing traffic

Here we risk being a motorcycle sandwich.  Once the traffic starts to move off again, its important to pick the right speed to rejoin the traffic otherwise we start to incur the risks of high speed filtering.<!--[endif]-->

Junctions, Traffic Lights and Roundabouts

When filtering it is often difficult to determine the safest place to rejoin the traffic, as there is always a temptation to go ahead just another few cars.  While filtering to the front of the queue will give us the maximum progress, those last few cars represent the highest risk.  Traffic at the head of the queue will not be looking out for a motorcyclist (particularly at roundabouts and junctions) as they will be searching for gaps in the traffic.  In addition at traffic lights, passing the lead vehicle introduces the risk of the lights changing to green just as we level with the car, where as joining one or two cars back, represents a significantly lower risk.  If we do get to the front of the queue while the lights are still red, we will need to move off promptly to avoid being shunted from behind, once the lights have changed.

As a motorcyclist, the consequences of being shunted into crossing traffic could easily be fatal.  Joining a few cars back increases our chances of being acknowledged by other drivers and gives us more time to prepare for moving off at the junction.  Drivers often don't correctly signal their intentions.  Many drivers will indicate right when going directly ahead on a roundabout or fail to indicate when turning right.

Other hazzards when filtering

You may have noticed the massive increase in the use of ‘advisory’ cycle lanes across the UK as the government attempts to encourage more people to use pedal cycles.  As a pedal cyclist (as well as motorcyclists) I hold the opinion that on-road cycle lanes do little to encourage pedal cycling as they are often in inappropriate and in inconvenient places.  I have also found that they discourage car drivers from giving you space when passing as the driver tends to see you as segregated in a different lane. 

Whether you agree with my view or not, on road cycle lanes pose a real danger to motorcyclists filtering queuing traffic, as they force the traffic much closer together leaving very little space to pass.

When filtering in urban traffic, keep an eye open for cycle lanes and expect your gaps to narrow (particularly when there are cycle lanes on both sides of the road).

Filtering Etiquette

Many drivers will choose to move out of your way when they see you filtering, which can often make your life a lot easier.  It is important to give them acknowledgement as this makes them feel appreciated and encourages others to follow suite.  Likewise if a motorist obstructs you, because they are not paying attention, it is important to be patient and not take risks.  Attempting to remove their wing mirror as you pass is not going to help you if you subsequently have an accident a few miles up the road and need sympathetic witnesses.  It will also discourage them from taking a positive attitude towards motorcyclists.  Many of those who appear obstructive are often not doing it deliberately, but simply haven’t seen you.  A friendly double toot of the horn can sometimes encourage them to move.  However, there are a small minority of drivers who either think filtering is illegal and dangerous or simply begrudge someone being able make progress while they sit and wait.  These people may take deliberate action to block you and you need to be particularly careful of anyone who appears to be blocking deliberately.  I recently had the pleasure of educating a taxi driver (who believed filtering was illegal) while being driven in heavy traffic, that motorcycles don’t cause congestion and that if 20% of single occupant drivers opted for 2-wheels, we’d see a lot less traffic queues.

When filtering on a motorway it is generally accepted that motorcyclists filter between the two lanes furthest to the right.  The advantage of this is that we don't tend to see trucks in the outside lane or find traffic pulling across to join and leave the motorway.  When filtering (particularly on motorways) you need to spend your time looking for where the hazards will be coming from.  Rear observation is less important, which might mean you fail to notice another faster rider approaching from behind.  If you do spot a quicker rider approaching, don’t be tempted to increase your speed, but look for a gap to move over and let him pass.  Likewise if you come across a slower rider, it is important to be patient and keep your distance.  Don’t be tempted to choose the inner lane as you will just reduce the amount of space available and discourage drivers from moving over.

On single carriageway roads filtering on the outside is normally the safest widest point and filtering on the inside of traffic represents the highest risk.  However, each queue will be different and sometimes the odd obstruction or vehicle turning may mean an alternate path is better.