Instead NSW drivers will be required to slow to 40km/h only where the speed limit is 90km/h or less. Drivers in a 90km/h zone or above will need to slow to a "safe and reasonable" speed, give "sufficient space" to those working on the roadside, and "change lanes to keep the lane next to the vehicle free if it is safe to do so."

In a statement, NSW Minister for Rural Roads Paul Toole said the changes made in NSW were about enabling drivers to slow down safely.

"If you are driving on roads 90km/h or over you will need to consider how close you are to the stationary vehicle and slow to a safer speed and give as much space to the vehicle as you can,' Mr Toole wrote in giving discretion to road users regarding the changes.

A similar law, introduced in Victoria in July 2017 and the ACT in April 2018, made it an offence not to:

'slow down to a speed that would enable you to stop safely when approaching and passing enforcement, emergency or escort vehicles that are stationary or moving slowly (less than 10km/h), and have either:

You must not exceed 40km/h when passing the vehicle and not increase your speed until a safe distance from the scene. The new road rule does not apply to vehicles on the opposite side of a divided road (separated by a median strip) from an emergency or enforcement vehicle scene.'

The ACT Minister for Road Safety Shane Rattenbury believes that "people can see the flashing lights [of emergency vehicles] and have plenty of time to slow down" and that feedback in the ACT has been "positive".

But the minister's view runs contrary to the key findings of an academic evaluation of the NSW trial, in which "some people interviewed suggested that the requirement for drivers to slow down to 40km/h was potentially dangerous in some situations".

The Victorian Minister for Road Safety Jaala Pulford has been contacted for comment as to whether the state government will undertake a similar review.

A Department of Transport spokesperson issued the following:

"This road rule was introduced to protect emergency responders and enforcement workers while on the job and working on the road. The rule requires drivers to slow down safely to 40km/h when there is flashing red and blue or magenta lights.

"We are continuing to monitor the performance of this road rule and are undertaking a review of its effectiveness."

The statement continued:

'Road rule 79A was introduced on July 1 2017, that requires drivers to slow down to 40km/h when passing stationary or slow moving (10km/h or less) emergency or enforcement vehicles with flashing red and blue or purple lights and does not cover tow truck or other special purpose vehicles.

'The rule must be well-established and understood among drivers, and its performance appropriately assessed, before any consideration can be given to potential amendment to improve effectiveness.

'We encourage all drivers to use caution when passing any vehicle on the roadside and drive to the conditions.'