[1] Together with route numbers and cardinal directions, these focal points aid the motorist navigating along a highway system.
Different countries have different practices as far as focal points on directional signs are concerned, and the term control city is not used globally.
Accordingly, local destinations on a sign, which only appear incidentally, would in a number of countries not be considered control cities.
However, all sorts of other potential destinations can be selected as control city, such as states and regions, frequently visited objects, and names of prominent intersecting roads.
Examples would be major bridges (the Golden Gate Bridge is a control city within San Francisco), tunnels (e.g. the Holland Tunnel in New York City), or mountain passes (e.g. the Gotthard Pass featuring prominently on signs in Switzerland).
The motorist accordingly needs to rely on the combination of the control city and the route number as navigation tools.
Possibly as a result of this, control cities tend to feature rather prominently on the route signs of European countries when compared to signage in North America.
In the German guidelines for directional signage on motorways, the concept of the Hauptfernziel (translating as main distant focal point) has a role that is comparable to that of a control city in North America.
The major towns of Germany typically double as Hauptfernziel on this basis, notwithstanding the fact that motorways often pass by rather than terminate there.
On the longer motorways of Germany, the distance between Hauptfernziele is usually some 150 to 200 kilometres (93 to 124 mi), though less in densely populated areas.
On longer non-motorways, a provincial capital often takes the role of control city despite not being close to the route's terminus or a major intersection.
Unlike the control city, these other towns are not necessarily to be found on subsequent signs along the route signposted.
Other than local destinations, signs in Scandinavia do not commonly feature other cities in addition to this major town.
One particular intersection outside London that made it to primary destination is Scotch Corner, the split between two routes from the South into Scotland.
On signs in the United Kingdom, cardinal directions are not used, but one specific aspect of UK signage is the use of regions as a focal point along roads.
As directional signs typically only contain the first one or two primary destinations, traffic needs to rely on the regional focal points to see the general bearing of the route.
Primary destinations that are not on the designated road are shown in brackets as in the image below: Canada lacks a coherently signed national highway system—even for the Trans-Canada Highway routes—and there is no mutual agreement for designating control cities across provincial boundaries.
For example, on Highway 401, Cornwall displaces Montreal as eastbound control city for most of the St. Lawrence valley.
Windsor, London, Toronto, Kingston, and Cornwall (with Montreal only signed along the short section between Cornwall and the Quebec border), are control cities while larger cities such as Oshawa and Mississauga are omitted due to them being suburbs of Toronto, although in the latter case this is common in most jurisdictions.
The Ministère des Transports du Québec typically uses large urban centres as control cities, even if they are far away and/or outside the province.
This may cause confusion to motorists unfamiliar with this convention, as the control cities may change at the continuations of these autoroutes into the adjoining jurisdictions; such as Cornwall (and then Kingston) being signed along Highway 401 in Eastern Ontario rather than Toronto.
The Trans-Canada Highway uses Edmundston, Fredericton, Moncton, and Sackville as control cities from north to south.
Route 95, the link between the Trans-Canada Highway and Interstate 95, uses only Houlton, Maine as a control city to the west.
[4] Control cities on other U.S. roads are often selected on the basis of general principles, as opposed to specific lists of towns.
On the other hand, there are also instances where intrastate control cities have been left out so that long-distance focal points could be added.
On the U.S. federal list, control cities have often been selected by virtue of being located close to an intersection of two US-interstates.
Freeways in Australia, while not using the term 'Control City', operate on much the same system as in the United States and Europe.