Ask Dr Dynamo

Dr Dynamo

Cycle lanes

Got a question about cycling? Write to Dr Dynamo!

Dear Dr Dynamo,

Why do some cycle lanes have a solid white line and some a broken white line?

Yours, John E, Fulbourn

Dear John,

Let’s start by making clear what we mean by a cycle lane, because I know some people don’t use the term correctly. A cycle lane is a strip of road, usually alongside the kerb, intended for cyclists. Cycle lanes are always part of the carriageway of the road. We never use the term ‘cycle lanes’ to refer to those cycle paths which are separated from the road by a kerb and sometimes by a strip of grass as well, and which are sometimes shared with pedestrians. These are given a variety of names: cycle paths, cycle tracks, or cycleways. But never cycle lanes.

‘Mandatory cycle lanes are mandatory for motorists, not cyclists’

A cycle lane is separated from the rest of the road by a white line painted on the road. There are two types of cycle lane: mandatory and advisory. Mandatory cycle lanes are marked with a solid, continuous white line. Advisory cycle lanes are marked with a broken, or dashed, white line. Both types of cycle lane may also be given a coloured surface to make them more obvious to drivers – in Cambridge a red surface is often used.

Image as described adjacent Image as described adjacent
Mandatory cycle lane in Trumpington Road Advisory cycle lane in Gilbert Road, where parking is always a problem

Mandatory cycle lanes

So what’s a mandatory cycle lane, then? Now the first thing to stress is that the term ‘mandatory’ refers to motorists, not to cyclists. It means that it is mandatory that motorists keep out of a mandatory cycle lane. It does not mean that it is mandatory that cyclists keep in the lane.

Motorists must not drive in a mandatory cycle lane, nor may they park in it – whether there are double yellow lines or not (though stopping for short periods to load and unload is sometimes permitted).

Advisory cycle lanes

An advisory cycle lane, on the other hand, is simply that – advisory. Motorists are advised not to drive or park in it, but it is not an offence to do so (though if there are yellow lines the usual rules apply).


Image as described adjacent
Advisory cycle lane in a relatively narrow part of Grange Road

Which is better?

Mandatory cycle lanes are clearly much better, and indeed the majority of cycle lanes in Cambridge are mandatory and have a solid white line. So why would the council ever bother to introduce an advisory cycle lane, with a broken white line? There are a number of possible answers:

  • Advisory lanes are sometimes used when the council doesn’t want to ban parking. A good example of such a lane is on Gilbert Road. The parked cars, though, make the cycle lane pretty useless.
  • Advisory cycle lanes are easier to implement – they don’t require a formal traffic regulation order, which means they can be introduced more quickly and more cheaply.
  • Advisory cycle lanes can be introduced in places where the road is too narrow for mandatory cycle lanes. This isn’t so strange when you think about it. Before the council can introduce mandatory cycle lanes it must ensure that the remaining road space is wide enough for all types of motor vehicles, including the largest lorries and buses. This is fair enough, since such vehicles are obliged by law to keep out of the mandatory cycle lane. Advisory cycle lanes can be introduced when the remaining road space is a bit narrower than that, since the occasional large vehicle can always spill over into the cycle lane without breaking the law. This obviously isn’t ideal, but if the number of wide vehicles is low it can work reasonably well.

This last situation is what has happened in Grange Road. The north end is the widest, and has mandatory cycle lanes. The south end is slightly narrower, and so the lanes are only advisory so that wide vehicles can stray into them. The central section is narrower still, and so has no cycle lanes at all.

I hope this answers your question, John. Happy Cycling!

Dr Dynamo

If you have a question about cycling, ask Dr Dynamo and he’ll try to answer it.