Miss the holiday airport crowds and expensive train tickets by sharing a stranger's car

Next weekend's bank holiday brings the height of the summer getaway upon us. Millions will be heading for the airports, the coast or the countryside for a break.

Put off by airport queues and crowded and costly trains, many will choose to travel by car. No wonder: a car is still a byword for convenience allowing you to get right to the door of your destination. But driving and car ownership are more expensive than ever, so how to get the convenience without the cost? This is where the plethora of newly launched car sharing or pooling sites comes into play.

The idea is simple: car drivers register their interest and where they are driving to on one of a number of websites such as blablacar.com, gocarshare.com, carshare.com and liftshare.com and they are paired up with potential passengers. The driver and passenger agree a price, date, meeting time and drop-off point. Costs of the journey are usually split 50-50, and if the car owner has an "any driver" clause in their insurance then driving duties can be shared too.

Regular commuters can save hundreds if not thousands a year, while savings can be also made on one-off journeys. And, of course, there are the environmental benefits of reducing the number of journeys.

The costs of registering vary. Gocarshare says users are free to make a contribution to the running of the site but there is no compulsory charge. Whereas blablacar.com offers free joining and doesn't charge either users or passengers – making money from advertising – and also has a very useful passenger cost calculator. The driver enters the start point and destination and any toll roads; the calculator then takes account of likely fuel use, average vehicle depreciation for the journey and a share of ongoing maintenance costs.

But the differences aren't huge. So, for example, a journey from London to Edinburgh will cost about £76 in fuel according to Google Maps but for the same journey, according to blablacar.com, each passenger in the car should pay £39. "We work on the HM Revenue & Customs figure that driving costs 45p a mile, but this would make long journeys too expensive so we tend to divide this by three and this is the suggested cost of the journey," says Nicolas Brusson, founder of blablacar.com. "The driver is free to adjust this up or down just as long as the price agreed at the outset is the price paid on completion of the journey."

Mr Brusson's firm – which was launched in France in 2006 and has more than 1.3 million users in Europe – gets most of its traffic from people travelling at weekends. "One model is based very much on one-off weekends away. We reckon that the costs for the passenger are about a third of the cost of the cheapest train ticket," he said.

People looking for a regular commuting partner may be better using liftshare.com, which is more about pairing up people travelling day in day out to a workplace and sharing costs.

James Fraser, 28, used blablacar.com for weekend trips to Paris to see his girlfriend and made substantial cost savings. "Although it takes longer, it cost about a quarter of a Eurostar ticket, plus the drivers have normally dropped me pretty close to my final destination, which helps. To date, the drivers have been nice and chatty, helping me to improve my French."

But getting into a car with a stranger does have safety implications. Although sites allow users to leave feedback – like eBay – on their experiences, precautions should still be taken.

Liftshare.com, for instance, recommends meeting in a public place, asking for ID of some sort to ensure you're travelling with whom you're supposed to be and telling friends and family all your trip details.