How is the speed of a traffic jam determined?
On this website, the speed at which every traffic jam is moving is indicated by a colour. The table below shows which colour represents each traffic estimation.
| description |
visualization |
At 70 mph on
Motorways |
At 60 mph on
Motorways |
At 30 mph on
A-roads |
| Slight delays |
 |
Between 32 and 44 mph |
Between 27 and 44 mph |
Between 14 and 25 mph |
| Moderate delays |
 |
Between 11 and 32 mph |
Between 9 and 27 mph |
Between 5 and 14 mph |
| Severe delays |
 |
Between 0 and 11 mph |
Between 0 and 9 mph |
Between 0 and 5 mph |
How are these speed estimates made?
TomTom uses multiple up-to-the-minute sources to determine the speed of a traffic jam.
- Data from Vodafone's GSM network. Vodafone knows when and where telephones are linked to a mast and where they are moving. This information is anonymised and sent to TomTom. TomTom uses this information to calculate the speed with which every telephone in a car is moving. In the case of traffic jams, cars move more slowly and thus the telephones move more slowly too.
- Data from TomTom users. Certain TomTom devices send anonymous information about their location and speed once the user has given permission to do so. Certainly when information from many different users is combined, this results in reliable traffic jam information.
- Data from third parties such as national and local governments and commercial traffic information providers.
TomTom combines these sources to produce a reliable estimate.