How to lane filter safely on a motorcycle

Filtering through slow-moving traffic is one of the biggest practical advantages of riding a motorcycle. It’s also one of the most nerve-wracking situations for new riders. In France, lane filtering (called circulation inter-files, or CIF) has been officially written into traffic law since January 2025, after nearly a decade of trials. But wherever you ride, the principles of safe filtering remain the same. Here’s a complete guide to doing it right.

What is lane filtering exactly?

Lane filtering means riding between the two leftmost lanes of traffic when vehicles are stationary or moving very slowly. It’s distinct from lane splitting (riding between lanes of moving traffic at higher speeds), though the terms are often used interchangeably in everyday language.

In France, the legal term is “circulation inter-files” (CIF). It applies only on specific road types, under specific conditions. In California, lane splitting has been legal since 2016 under Vehicle Code 21658.1. In the UK, filtering is legal provided it is done safely, though there are no specific speed limits. Rules vary widely from country to country, so always check local regulations.

The French legal framework since 2025

After two rounds of government-backed trials evaluated by Cerema (France’s transport research agency) between 2016 and 2024, the French government enacted decree No. 2025-33 on January 9, 2025, making lane filtering legal nationwide.

Who can filter?

Only two-wheeled and three-wheeled motor vehicles with a maximum width of 1 metre. Sidecars, quads, and motorcycles with wide panniers fitted are not eligible.

Where is it allowed?

Lane filtering is permitted only on roads and motorways that meet all three criteria: dual carriageway separated by a central reservation, at least two lanes per direction, and a speed limit between 70 and 130 km/h. This means motorways, ring roads, and expressways. Not city streets, not single carriageways.

Under what conditions?

Filtering is only allowed when traffic is dense enough to form uninterrupted queues across all lanes. A brief slowdown doesn’t qualify.

Speed rules:

• Maximum speed while filtering: 50 km/h (about 30 mph)
• Maximum speed differential with adjacent traffic: 30 km/h (about 19 mph)
• If one of the two lanes is at a standstill: maximum 30 km/h (about 19 mph)
• As soon as one lane reaches 50 km/h, you must rejoin normal traffic flow

Overtaking another motorcycle that is already filtering is prohibited.

Penalties

Breaking the rules carries a fine of 135 euros and 3 penalty points. Enforcement can be done via automated cameras, without the need for a physical stop.

What does the research say?

The evidence on lane filtering safety is nuanced but broadly encouraging, provided riders keep their speed in check.

Key findings from French trials (Cerema, 2016-2024): accident rates for motorcyclists on filtering-enabled roads remained stable during the second trial period. Fatal accidents involving a rider in a CIF situation averaged between 1 and 6 per year across the entire test network. Compliance with the 50 km/h limit improved from 23% in 2015 to 40% in 2018, though one in two riders still exceeds it.

The widely cited UC Berkeley study (Rice et al., 2015) analysed 6,000 motorcycle collisions in California and found that lane-splitting riders were significantly less likely to be rear-ended. However, crash risk increased sharply once the speed differential exceeded 15 mph (about 25 km/h). The study concluded that filtering appears to be relatively safe in traffic moving at 50 mph (80 km/h) or less, provided the rider doesn’t exceed surrounding traffic speed by more than 15 mph.

The main takeaway from all available research is consistent: speed differential is the number one risk factor. Keep it low, and filtering is statistically safer than sitting in traffic where you’re exposed to rear-end collisions.

10 practical tips for safe lane filtering

1. Respect the speed limit (seriously)

Whether it’s the French 50 km/h rule or the general 15 mph differential guideline, speed is the single biggest predictor of filtering accidents. At 50 km/h, you need roughly 14 metres to stop. At 70 km/h, that becomes nearly 20 metres. Between two lanes of cars, those extra metres are the difference between a close call and a crash.

2. Cover your brakes

Keep one or two fingers on the front brake lever and your foot hovering over the rear brake at all times. You need to be able to stop instantly. Never ride through traffic with open hands on the grips.

3. Watch the front wheels of cars

The front wheels of a car turn before the car itself moves. This gives you a split-second earlier warning than waiting for the car to move into your path. Also check car mirrors: if you can see the driver’s face in their mirror, there’s a good chance they can see you too.

4. Stay between the two leftmost lanes

This is the legal requirement in France, but it’s also the safest position everywhere. Right-hand lanes see more lane changes (merging, exiting) and tend to have tighter gaps.

5. Make yourself visible

Ride with your headlight on (mandatory in most countries anyway), wear reflective gear or bright colours, and consider a light-coloured helmet. Some riders briefly flash their hazard lights when entering the filtering zone to signal their presence.

6. Never force your way through

If the gap narrows, slow down or stop. Don’t honk, don’t slap mirrors. Filtering is not an absolute right of way. If a vehicle blocks your path, wait. Patience is protective gear you can’t buy.

7. Be extra cautious around trucks and buses

Large vehicles are wider, their drivers have larger blind spots, and they may not expect a motorcycle alongside them. If the gap looks tight, wait for them to pass before continuing.

8. Watch out for merge zones and exits

Motorway on-ramps, off-ramps, and junctions are where drivers change lanes most frequently. Slow down as you approach these areas and be ready to stop.

9. Adjust to conditions

In wet weather, road markings become slippery, visibility drops, and braking distances increase. Filtering may still be legal, but common sense should dictate a slower pace — or simply staying in your lane.

10. Never overtake another filtering rider

It’s illegal in France and dangerous everywhere. If the rider ahead is going slower than you’d like, stay behind. They may have spotted a hazard you haven’t.

A note for car drivers

Lane filtering works best when it’s a two-way effort. In France, filtering awareness is now part of both motorcycle and car driving tests. If you drive a car, the most helpful things you can do are: check your mirrors before any lane change, always use your indicators, and leave a reasonable gap between the two leftmost lanes when traffic slows. In the Paris region, which accounts for 40% of all CIF-related accidents, coexistence between riders and drivers remains the biggest challenge.

Conclusion

Lane filtering is a right, not an obligation. If you’re not comfortable, if visibility is poor, or if traffic is too unpredictable, there’s nothing wrong with staying in your lane like any other vehicle. The golden rule is simple: never ride faster than your eyes can scan. If you can see 20 metres ahead, ride at a speed that lets you stop in 20 metres. Everything else comes with experience, patience, and attention.