One hundred and fifty garda cars are to be purchased at a cost of €3m to quell growing concerns over the high mileage on some of the force's fleet of vehicles.

There are currently 2,749 garda cars in operation but a significant proportion of the fleet are more than four years old. When garda cars clock up 300,000km they are no longer considered safe to drive and are taken off the road. Around 100 garda vehicles are due to be decommissioned at the end of the year.

The €3m for the new vehicles is the first garda draw-down from the contract the National Procurement Service has entered into with Toyota Ireland. They are expected to be operational before the end of the year.

There have been growing concerns, particularly in rural areas, over the availability of squad cars. In August, several garda cars were forced off the roads because of high mileage. Justice minister Dermot Ahern told the Sunday Tribune: "I am pleased that funding is available for the purchase of an additional 150 cars for the garda fleet. The fleet has expanded significantly in the last five years – up by over a quarter. It is vital to continue to renew the fleet on an ongoing basis and to ensure that we continue to focus our efforts, despite the economic difficulties, on frontline policing services."

A source who works in a busy city centre Dublin station which deals with a substantial amount of gangland activity, including high-speed chases, said that urban stations were also being affected by the ageing fleet of cars.

"These cars are long overdue and we just hope we do get them as promised.

"The age and condition of some of the cars is a serious problem that's becoming worse. If you look around at garda cars in Dublin city, they are all 2006 and 2007."

It emerged earlier this year that no new patrol cars had been bought for two years. However, the authorities had purchased a large amount of new vehicles in 2006 – 60% of the entire fleet – after a late allocation of €17m from the exchequer.

Last month, it emerged that two bulletproof BMWs seized from criminals by the Criminal Assets Bureau (CAB) are now being used as garda cars.

The emergency response unit (ERU) has been using them in Limerick on high-risk gangland operations.