A government change means the Dion's bus is no longer No1

But don't worry, the bus itself still exists - but the route number has gone up 89 places and is now called Route 90.

It's a similar deal with Route 1U (now route 91), Route 4 (92) and Route 4U (93).

The timetables for all these services remain unchanged.

The change has been driven by Transport for NSW, which is looking to standardise route numbers across its contracted services.

"Standardised bus numbering and the removal of duplicate numbers in each region is making public transport in NSW easier for customers to use," a Transport for NSW spokeswoman said.

"A specific route number range is developed and applied for regions across NSW.

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"In the Illawarra region, bus numbers are being changed to a new two-digit format and school bus services will be indicated by an 'S' in front of the number."

The Dion's bus route likely acquired the No1 tag sometime shortly after 1955, when the Department of Motor Transport took control of approving routes.

Dion's manager Les Dion said the change took effect on Monday and, while he said it hadn't affected him, some of the drivers felt an "emotional attachment" to the No1.

Mr Dion said there had been no complaints since changeover and suggested it was because most people look for the destination rather than the route number.

"The other reason it's gone down quite smoothly is that there's been absolutely no changes to the timetable," he said.

"They see the bus come, they see the destination name, they see their driver and they know to get that bus."