On British roads (especially dual carriageways or motorways), signs indicating heavy traffic are a regular occurrence. The most common ones are:

  • Congestion caution
  • Congestion ahead
  • Congestion after some location, e.g. junction

and also

  • Queues possible
  • Queues likely
  • Queue ahead
  • Queue after some location, e.g. junction

and even

  • Caution, queuing traffic

I've been driving in Britain for the past 10 years and generally have come to understand that queue is worse than congestion and ahead/after xxx is more certain than caution or likely. However are there any specific meanings attached to these wordings? Are there any rules about using one over another?

  • 2
    Generally when people/cars are in a queue, they spend some time moving slowly forward, but a lot of time not moving at all. Whereas congestion for traffic simply implies many/most/all cars are not moving as fast as the drivers would like (because the car in front is likewise constrained). The "after [junction]" form is used in contexts where you might decide to leave the main route to avoid a hold-up. The "possible/likely" versions are fixed (always there), as opposed to the others which are "intelligent" (based on actual current traffic conditions). – FumbleFingers Oct 2 '14 at 13:35
  • 3
    You seem to think that the Great Traffic Controllers in the Sky have a clear and consistent approach to their ministerial machinations and sage communications. What leads you to this point of view? – bib Oct 2 '14 at 14:18

In traffic management the concepts of "congestion" and "queue" are as you surmised.

Congestion is when there is increased traffic, or heavy traffic. The effects of congestion are slower speeds, increased travel time and the possibility of queues.

A queue is when traffic is stationary, i.e. congestion is so bad that cars will come to a complete stop.

I am not aware of any specific guidance for use of the qualifiers, e.g. "ahead", or "after next junction".


The use of congestion is defined at length on the Highways Agency website. In summary it does refer to heavy traffic that is moving as freely as may be expected. While a queue is traffic that is moving slowly, if at all.

For the signage of queues:
. Queues possible is usually used around roadworks to indicate that there may be a queue.
. Queues likely is used as a fixed sign where queues build up in the rush hour. . Queues after is used on motorways and does indicate after a particular junction. . Queues ahead seems to be a catchall for everything else.


The OP states that a queue is worse than a congestion, and the phrase queue ahead/after xxx expresses greater certainty than the terms caution and likely.

Dictionary.com defines a queue and a congestion as

(British English)
queue: a line of people, vehicles, etc, waiting for something: a queue at the theatre
congestion: noun 1. the state of being overcrowded, esp with with traffic or people
e.g., The city has become gridlocked, with rush-hours replaced by semi-permanent congestion

Oxford Dictionaries Online says

queue chiefly British A line or sequence of people or vehicles awaiting their turn to be attended to or to proceed
e.g., Vehicles previously stuck in queues past the A2 junction suddenly speed up and try to get the best position as three lanes expand to eight for the toll booths.
congestion The state of being congested
e.g., The bus lanes are designed to ease traffic congestion but they remain controversial

But that depends where your focus lies. If it is speed, then yes, a sign informing motorists that there will be queues ahead will almost certainly mean that drivers should expect significant delays. Traffic will move at a much slower pace. A sign informing about possible congestion ahead will mean that traffic will be much slower than normal but it is less likely that drivers will be at a standstill.

However if your focus is of safety, then I would argue, signs warning of congestion ahead should be taken more seriously, motorists would do well to employ defensive driving measures. Congested traffic is more likely to lead to road accidents because of a "Higher chance of collisions due to tight spacing and constant stopping-and-going"

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image: European Approach to Congestion Management

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Source: Traffic England

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