A report by the Criminal Justice Inspection (CJI) has expressed disappointment at the delay in establishing a unit to investigate fatal and serious crashes in NI.
The CJI had urged the creation of a dedicated collision investigation unit in 2008.
But it said the unit only started "a few months" ago.
The PSNI said the unit had taken longer than anticipated but it was recruiting for more staff.
Deputy Chief Inspector of CJI, Brendan McGuigan, said he believed the collision investigation unit could have been introduced sooner.
"Inspectors viewed this recommendation to be of critical importance," he said.
"While we welcome the attention the current Head of Roads Policing has given to taking it forward, we believe the collision investigation unit could have been introduced sooner.
"The resourcing of the new unit should also be monitored on an ongoing basis.
"This will ensure that if an increase in the current number of fatal and serious road traffic collisions occurs in future years, this unit will have the capacity to carry out additional investigations."
Mr McGuigan said he feared that if the PSNI did not supplement the unit's staffing levels, officers could be "burned out" or "overwhelmed" by the number of cases they have to deal with.
In a statement in response to the CJI report, the PSNI said the establishment of the unit had taken longer than anticipated, "due to a number of factors, also noted and acknowledged by the deputy chief inspector".
It said it had established a collision investigation unit comprised of six specialist officers and was "currently recruiting a further eight officers from our current road policing establishment, in order to fully meet the recommendations contained within the original report".
"Road deaths have been falling. So far this year, 51 people have been killed in road traffic collisions on roads across Northern Ireland, a reduction of 49 in comparison to this time last year," the PSNI statement added.
"The Police Service is never complacent about road safety.
"One death is one too many. We remain committed to our long-standing strategy of targeted enforcement coupled with education."
The CJI assessed the work undertaken by the Police Service of Northern Ireland since the 2008 report.
It acknowledged the efforts made by the PSNI to take forward its recommendations.
The CJI welcomed the force's implementation of the Association of Chief Police Officers (ACPO) speed thresholds since June, but said it would have wished to see a "quicker response".
It also welcomed increased co-operation between PSNI officers and Irish police officers.
Mr McGuigan said there should be a desire to lower the drink drive limit in Northern Ireland and that this "should be done simultaneously with the Republic of Ireland where legislation has already been passed to lower the legal limit to 50mgs from September 2011".