On the face of it, carpooling is an ideal solution to gridlock. Not just to and from work, but on school runs, shopping trips, and leisure journeys like football matches.
People have been doing it for years. School-run mums have shared that chore, and pal dads going to Croke Park from the same town regularly share cars to follow their county teams. Work colleagues who happen to be neighbours often use the car sharing system in their own informal way.
But organised commuter carpooling on a large enough scale to make a significant difference to overall traffic congestion is more complex, and more difficult to operate. Matching drives to a particular work location between strangers who have homes in the same general area is not a simple matter of putting an advertisement in the local paper.
Gender matching, preferences such as non-smoking, and even entertainment compatibility all have to mix properly if individual arrangements are to work.
And there are sociological impacts, such as people's needs for privacy, which militate against mass carpooling being successful.
In fact, after several decades of experimentation in many different countries, with many different systems, there's an increasing belief that car sharing is a flop.
In the US, from where systematic versions have mostly evolved, carpooling declined in the decade up to 2000 from 13.4 per cent of work journeys to 11.2 per cent. And the percentage is still dropping, despite the expenditure of billions of dollars in adding special dedicated carpool lanes to congested highways.
In Ireland, although a number of internet-based car sharing initiatives have been set up, it's hard to get a handle on how well they're going.
One success story indicates the environment in which carpooling on a reasonable scale can work: in companies which have a very high level of employment concentrated in the one area.
Last year Intel Ireland started a carpooling scheme at its complex in Leixlip, Co Kildare. With more than 4,000 employees, it might seem that the 300-plus of those who regularly share rides to work in each others' cars is small, but on the basis that not every Intel employee drives to work, one company estimate puts this at between 10 and 15 per cent of those who do.
Intel set up a special carpool section on its internal intranet, where those interested could match their journey needs with others.
The company also provides carpool parking spaces near the entrances to its various buildings. "This has been particularly appreciated, because nobody else who works here, even top management, has a dedicated parking space," says an Intel spokesperson. "But people who carpool have a special windscreen sticker that allows them to use the dedicated spaces."
The Intel system doesn't try to match people tightly. Instead, those interested simply register their home locations and commuting times. Registered people are alerted by internal e-mail when someone with a matching home and time location comes on line. It's then up to the individuals concerned to make contact and arrange things between themselves.
It gets more difficult in the new business park developments, which typically have many different businesses, The "community factor", and the security and comfort this provides, is not so strong as in the Intels of this world.
But the originator of one system provider for such multiple business locations has set up web-based carpool operations for areas which include Park West, Belfield/Beechill Office Park, Central Park in Sandyford, and CityWest Business Park at Saggart.
Peter Seymour says that a fundamental requirement for successful operation of any carpool scheme is that it is proactively promoted by employers.
"There are successful schemes in Britain because the British seem to take such initiatives seriously," he says. "And in business parks there is potential for a web-based system to work, because what it does is take down the screens between the individual businesses in the parks, and opens up more potential pairings."
He'd like to see more internal systems within the individual businesses to incentivise their employees to get involved in car sharing, rather than depend on the "passive" signage which is all the business park managements can realistically do.
The sites which Seymour has set up provide the usual security guidelines about setting up meetings with people who can often be complete strangers. These have been well sorted in the US scenario, where the scale is greater and so are the perceived dangers.
But in Ireland it might just be a case of unmatched personal chemistry. "Here, there's a very long chance that you might just be teaming up with an axe murderer," Seymour quips. "In actual fact, it's more likely a case of people just not getting on. If that's it, I say people should just walk away from the arrangement."
According to Professor James Wickham of the sociology department in TCD, the phenomenon known as "carcooning" can also stall carpooling initiatives at a personal level. "People personalise their cars, particularly their sound systems, which are especially important when you're stuck in traffic," he says. "I might prefer Bach, and a potential car-share person might prefer something else, and that can cause conflicts."
He also hypothesises more fundamental reasons why carpooling has had indifferent success in today's commuting world. "Car sharing works best when everybody is coming from the same neighbourhood and working in the same place," he says. "But today, journey-to-work patterns have become more flexible in start and finish times, paradoxically because of the traffic situation. It doesn't suit carpooling, which makes it all a vicious circle."
The school run also interferes with the car sharing idea because, for those closer to their work, dropping children to school is part of the commute. Which might not suit many potential carpool candidate. And anybody who can be delayed by social or business aspects of their work simply cannot get involved in a carpool.
But there is increasing pressure for imaginative methods of cutting down private commuting traffic on Ireland's roads. When assessing planning applications for major office developments, particularly in dedicated business parks, local authority planners have "shifted gears" in terms of car parking spaces.
"What we used to call the 'minimum requirement' of one space per 25 square metres of office space five years ago, we now look on as the maximum allowed," says a senior planner in one Dublin Co Council.
"We now require a Mobility Management Plan from each development that deals with the nitty gritty of daily operational management of traffic and people movement. This must incorporate parking space assignment, public transport, whether the company involved will provide a private bus service to encourage employees not to use their cars.
"Restricting the available car parking space is one way of cutting down the use of cars on a development."
Car sharing may be in decline. But so are parking spaces, which might still halt that decline in the future.