A Phantom Queue is a phenomenon in traffic, where queues and delays are caused without any apparent reason.
Possible causes of Phantom Queues
Recent research indicates that one possible cause for phantom queues is a combination of drivers who are impatient, and drivers who are nervous. On the motorway/highway, impatient drivers are likely to weave from lane to lane in an attempt to stay in the fastest-moving lane. The action of wanting to get there faster than the other drivers, may actually cause delays.
It is believed the reason for this is that the capacity of a stretch of motorway is effectively reduced by up to 15% when someone is in the process of changing lanes. When one person is changing lanes, this may further inspire other drivers to do the same.
The chronic lane changing by the impatient drivers causes effects which is very similar to sections of motorway where two lanes of traffic have to merge. On these stretches of road, nervous or overly cautious drivers are likely to apply the brakes and slow down more than what is actually required, which causes a ripple effect of slowing traffic.
When faced with being cut off - even if the cut-off is not necessarily dangerous in the slightest, a nervous driver will go directly for the brakes, which causes the driver behind to slow down, etc. Because it takes more time to accelerate than to slow down, a matrix of impatient and cautious drivers can cause a chain reaction which can bring traffic from a healthy-flowing 70mph to a complete standstill - all without any obstacles, accidents, or road enforcements in place.
How to keep traffic flowing
Whilst research on phantom queues is not complete, and no definite answers are given, there are some guidelines you can follow that will help. The most important rule is to keep plenty of distance between you and the car in front. This open space acts as a buffer which you can use to keep acceleration and braking to a minimum - try to find a speed which allows you to drive at an even speed. If traffic slows down in front of you, wait as long as possible before hitting the brakes yourself. Unnecessarily braking causes the exact problems detailed above.
When driving in medium-heavy traffic that still flows, but is showing signs if restrictions, pick a lane, and stick to it. Even if your lane is the slow one now, chances are that it will pick up speed and be the fast lane in a minute or two. A little bit of patience pays off in the long run.
The last tip is perhaps the most obvious: If there are fewer cars on the road, there are fewer chances to make traffic congestion. Ride with a friend, or get someone to ride with you instead of taking several cars. Finally, if you can avoid the busies stretches of road, either by traveling via alternative routes or by traveling at an alternative time, you aren't part of the problem, and won't have to be annoyed by traffic jams!
See also Starting a traffic jam