WOLO is the name of a special type of railway telegram which is used in NSW to inform train crewing and other operations staff about temporary heat-related speed restrictions which are applied if the ambient temperature is predicted to rise above 30 C, and certain other conditions are met.

Generally, WOLO telegrams are only issued for sections of track built with continuously-welded rails. Most of the time, but not always, this will also mean track sections laid on concrete rail ties (aka sleepers).

WOLO restrictions usually apply between 1000 and 2000 on the day of issue. If a WOLO telegram is required on any subsequent days, a new telegram is issued for each day that the restrictions are in force.

The term 'WOLO' unofficially means 'Warning Of Low Overhead' in reference to the fact the the original method of overhead wiring suspension using fixed tie-off points would result in sagging contact wires on hot days. Gradually this type of suspension is being replaced and all new work or renewal of old overhead wiring done since the mid-1980's is set up with weighted tie-off points that use a set of pulleys and vertically-suspended cast-steel weights to keep keep the catenary and contact wires under constant tension at all times, even during extremes of heat, so sagging is almost completely overcome.

Colloquially, however, the term 'WOLO' is expanded to mean 'Welded track - restrictions on speed of Operation of LOcomotives'.

'WOLO' is just one of many standard telegram codes issued by the Sydney Telegraph Office, which these days is not a telegraph office at all since there's no such thing as a real paper telegram any more (FYI, Tel$tra discontinued their telegram service in the early 1990's).

When WOLO restrictions come into force, a reflective yellow sign with the word 'WOLO' in large black letters is displayed so it's visible by the drivers of all passing trains at a prescribed list of signalling locations, and also at some train crew sign-on rooms.

Listed below is a table of maximum speeds a passenger train can travel at during WOLO conditions: