Safety & Rules
Riding Beside a Lorry Is a Geometry Problem
Large vehicles turn by sweeping their trailing wheels across a path the cab never occupies, which creates a closing space that no amount of rider attention can escape.
Collisions between bicycles and large goods vehicles are a small share of incidents and a large share of serious ones. The mechanism is geometric rather than behavioural.
Long vehicles cut the corner with their rear wheels
A vehicle turns about a point determined by its steering axle. The further behind that axle a wheel sits, the tighter a path it follows through the turn.
On a long rigid vehicle or an articulated one, the rear wheels track well inside the front. The cab may swing wide while the trailer passes close to the kerb.
A rider positioned between the vehicle and the kerb is in a space that closes as the turn progresses. There is nowhere to go by the time it is apparent.
The cab is high and the sight lines are poor
A driver seated high above the road has a substantial blind area immediately in front of and beside the cab, extending several metres.
Mirrors and camera systems reduce this and do not eliminate it, and checking them all takes time a driver may not have while managing a turn in traffic.
Modern vehicles increasingly carry direct-vision glazing and detection systems, which help. Older vehicles remain in service for a long time.
Filtering up the inside is where the risk concentrates
Traffic stopped at a junction invites riders to move forward along the kerb side. That places a rider precisely in the closing space at precisely the moment the vehicle moves off.
A vehicle waiting at a junction may be intending to turn without signalling, or may be signalling in a way that is not visible from beside the cab.
The reliable adaptation is not to pass a large vehicle on the inside at a junction at all. Waiting behind costs seconds and removes the mechanism entirely.
Position ahead or well behind, not alongside
Where a rider is already ahead of the vehicle and clearly visible over the front, the geometry no longer applies. Stopping well forward of a stop line achieves this.
Where that is not possible, remaining behind is the alternative. The dangerous position is the one in between, alongside the length of the vehicle.
Advanced stop areas at junctions exist for this reason. Their value depends on reaching them by a route that does not involve passing along the vehicle's side.
Air movement is a secondary effect
A large vehicle passing at speed displaces a considerable volume of air, first pushing a rider outward and then drawing them in behind it.
The effect is stronger with flat-fronted vehicles and increases sharply with speed. It is felt as a shove rather than as a gust.
Riding a straight and relaxed line while it happens is the correct response. Tensing on the bars converts the air movement into a steering input.
Questions readers ask
Is it worth reporting a near miss if nobody was hurt?
Where a scheme exists, yes, because clusters of reports at one location are what supports a case for changing it. Where none exists, reporting the location to the road authority is still the mechanism that gets a design looked at.
What should I write down after a near miss?
Location, time, direction of travel, what the road looked like and what restricted anyone's view. Photographs of the location taken later are more useful than a description. Skip the part about whose fault it was.
