Emergency telephone

The system Harman envisaged was a series of telephone units in a box on a short post, spaced every 160 metres (0.1 mi) on Perth's freeways.

Picking up the handset would trigger an alarm in the Main Roads control centre and police, fire or ambulance could then be determined by the caller.

Harman developed the system with the approval of the main roads commissioner and chief engineer, by adapting the existing design of communication facilities used at the security firm in which he worked.

In the United Kingdom, orange "SOS" call boxes are spaced every 1.6 kilometres (1 mi) on all motorways as well as some major "A" roads, with roadside markers indicating the nearest phone.

Emergency telephones were installed every 0.25 miles (400 m) on all limited-access highways ("Freeways") throughout Southern California in the United States beginning in the 1970s.

[2] On Italian "Autostrade" ("Motorways"), "SOS" emergency phones, generally coloured in yellow, are found spaced every 2 kilometres (1.2 mi).

[8] Improving coverage of the cellular network in combination with high maintenance and upkeep costs have resulted in declining usage of emergency telephones for highways.