Road safety advocate Peter Frazer ensures Sarah's rule becomes law

The rule mandates drivers to slow down and move over at a car crash, when an emergency service vehicle has lights flashing or if someone has broken down. If in an 80km/hr zone or below, drivers must reduce their speed to 40 or face a fine.

The hand of the government was forced into action following the death of 23-year-old Blue Mountains woman, Sarah Frazer in 2012 and the road safety campaign mounted by her father Peter Frazer afterwards.

Ms Frazer's car broke down on the way to university. Along with an NRMA tow truck driver Geoff Clark who had come to her aid, she was killed in the emergency breakdown lane on the Hume Freeway near Mittagong.

From September 26 there will be a permanent expectation that drivers will be forced to slow down when passing vehicles that have broken down or face a fine.

Roads Minister Andrew Constance said they had adapted the trial, so drivers in a 100 km zone did not have to reduce their speed to 40 but instead cut their speed to "safe and reasonable" while moving over.

"Anyone travelling in an 80 km speed zone will be required to drop their speed to 40 kms, if they are passing a highway patrol or emergency services vehicle, a tow truck or a roadside assistance vehicle," Mr Constance said.

"For those high speed limit areas we are going to require drivers to slow down and move over ... it is very hard to slow down to 40 km an hour, particularly in the regions."

Sarah's father Peter Frazer said he was "pleased" by the the government's decision.

"The NSW government has chosen to protect, not only our police and emergency services, but our roadside assistance personnel and tow truck drivers," Mr Frazer, president of SARAH (Safer Australian Roads and Highways) said.

"This amended rule recognises that as all lives are precious, all those in harm's way have a right to get home safe... everyday... no exceptions."

Mr Frazer said in his daughter's case, the breakdown lane was not built to the three metre Australian standard and while the tow-truck driver was hooking up her car, a passing truck side-swiped the broken-down car killing both instantly. The driver was given an 18-month jail sentence.

Mr Frazer gathered 23,000 signatures in a petition to bring in the slow down, move over rule and to fix roads to agreed Austroads standards.

"No one slowed down to give these vulnerable road users the space they needed ... I know this because Sarah had left me a voicemail saying cars and trucks were passing her at high speed just centimetres from her vehicle.

"When you see flashing lights on the road ahead, commit to drive so others survive. Everyone's got a right to get home safely," Mr Frazer said.

Mr Constance said some 85 per cent of accidents on NSW roads in the last five years have happened in 80km (or lower) zones.

Mr Frazer said he was now determined to see the rule rolled out in its entirety nationally.