The possibility of vehicles powered by low energy nuclear reaction (LENR) or cold fusion devices raises some intriguing possibilities and some fascinating questions. Even if such devices cannot be used to directly power cars they could be used to greatly lower the cost of electricity and make electric cars viable or to greatly lower the cost of oil production and drastically slash the cost of diesel fuel and gasoline.
http://www.youtube.com/watch?v=e8JhwjgFzbA
This would obviously greatly reduce the price of driving which would have some interesting effects upon the average driver. The first and most obvious would be traffic congestion. If driving becomes cheaper more people will drive more and there will be more vehicles on the road. The problem with that is that the roads aren’t getting any bigger. The video of the 401 between Toronto and London in Ontario (the busiest highway on North America which I drove on last month) ably demonstrates my point. Do you want to drive on that every day I don’t.
In many cities there simply isn’t enough room to expand the existing road systems even if the money to do so were available. One negative effect of LENR might be more gridlock and longer commutes. Governments might end up having to restrict the number of cars upon the road. It has always been proposed in London and New York.
Even if there is enough room on the road there is still the problem of parking. Parking spaces are already in short supply in many American cities including Denver and Los Angeles. Since urban and suburban land is getting more expensive more and more parking lots are being redeveloped into housing or retail space which makes the situation worse.
One result of this might be severe limitations or high costs of parking in many cities. Many people will end up having to park miles from their destination and take a bus, a cab or a train to where they are going. Our future might not be flying cars but crowded park and rides.
Naturally in such a situation many people will stop driving all together or drive only occasionally. Alternatives like mass transit, short term car rentals, car sharing and cabs will become more popular. Some news outlets have already noted a trend of fewer younger people driving. I have a feeling that’s a trend that will continue even if the Republican Party doesn’t want to see it.
Then there’s the size of vehicles if the cost of driving becomes incredibly low (it’ll never be free, “free energy” is wishful thinking) the size of vehicles will increase perhaps to idiotic proportions. One correspondent I’ve dealt with has dreams of everybody driving a “pimped out motor home” to work. There are some obvious reasons why that wouldn’t work.
There wouldn’t be enough room on the road for all of those behemoths nor would there be enough parking. Anybody that’s ever followed a motor home up a winding Colorado highway knows how such monstrous vehicles congest traffic. At some point the number of such pimped out goliaths on the road will have to be curtailed.

These aren't semis they're motor homes. If motor homes this size become popular they'll generate nothing but gridlock.
One likely scenario is that such vehicles would simply be banned. After all why should a small percentage of the population be allowed to block the public highways that everybody else is paying for with their taxes? Unlike trucks; which are needed to haul the goods that make our economy move, motorhomes serve no public purpose. What happens when the trucks hauling the food to the stores can’t get through because the roads are blocked by morons driving oversized palaces on wheels? The trucking industry might take the lead in trying to get motorhomes or private vehicles over a certain size banned at some point.
Beyond that nightmare there’s another one that the free energy fantasists don’t like to consider: building and maintaining roads costs money. In the United States, highways are paid for with fuel taxes. Most American governments aren’t able to properly maintain the roads with today’s fuel taxes. If taxes fall drastically and traffic increases dramatically because of LENR other answers will have to be found.
The most obvious solution would be some sort of electronic toll system which would charge drivers every time they used the road. Such a system would be a lot fairer than today’s gasoline tax because it would only charge those that actually used the road. It would also be more practical because it would be a lot harder for politicians to divert the toll money for their pet projects. In many American states gasoline taxes are spent on everything but the highways. Yet it would not be popular because a large percentage of the population buys into the myth that highways are free.
The LENR highway will be cheaper but it probably won’t be that much fun. It’ll be more crowded, more expensive and probably gridlocked. Perhaps LENR enthusiasts should look to more practical answers such as high speed trains or Maglev to meet our transportation needs.

You may be overthinking things. More people drive out of necessity than pleasure. If I drive downtown to work, it’s because I need my car there for some reason. It’s not the gas cost that prevents me, but the parking costs and the heavy traffic. So if I’m going downtown, I’ll take the train regardless of gas costs.
So I doubt if lenr will make city driving much worse.
On the other hand, with cheap gas, I would be more likely to drive away from the city for pleasure. But again, it’s not the gas costs that stop me. And no, I’m not independently wealthy.
If gas were free, I’d probably switch to a bigger vehicle though. But it won’t be until driverless cars that I’d really travel for pleasure.
People drive for a wide variety of reasons. Many Americans and Canadians drive because there is no alternative transportation available. City driving is already bad and will get worse. Although at some point driving will be restricted in most cities if just to keep the streets clear enough for fire trucks and ambulances to get through. Interestingly enough when I lived in the city with no car the biggest hassle wasn’t getting around that was easier. It was shopping. That was the only time I missed having wheels. As for bigger vehicles that depends on how big. Gas will never be entirely free.
same problem as you, probably worse in France.
Streets are tighter, more buses that make the global speed at 15kph max for all vehicles. terrible parking that block buses and trucks.
Development of scooters and 3wheel motorbikes that you can drive with a car license. More and more bikes, electric bikes, despite weather and traffic.
for me, with my bike, I go faster than car on pure city (ok, if there is a highway I lose).
for shopping I have the solution:
http://www.lenrforum.eu/download/file.php?id=20
for kid, I have another trailer, much better/safer than the seat.
For my wife… I failed to convince.
True I’ve noticed that in many cases you can get across town faster in Denver Colorado on the bus or the train than by driving. What about those of us who don’t like riding bicycles. Of course there’s another solution for shopping. When my father was a boy my grandmother simply called the A&P market in the town where he grew up and they delivered the groceries. In Denver Colorado the King Soopers grocery chain which is part of the Krogers conglomerate already has delivery trucks. I have a feeling that’s the future.
There are other interesting technologies arising that may mitigate traffic issues and LENR, should it take off, would in turn help to accelerate the adoption of such. Just look up Google’s self driving car initiative, which has several US states already making laws pertaining to the usage of already (see California and Nevada as examples). Projections are already saying that if a small percentage of cars on the road, I believe the amount was around 10%, it would have a gigantic effect on reducing traffic congestion and accidents.
Here’s a couple links to provide some information:
http://www.cnn.com/2012/09/25/tech/innovation/self-driving-car-california/index.html
http://www.theatlantic.com/technology/archive/2012/08/googles-self-driving-cars-300-000-miles-logged-not-a-single-accident-under-computer-control/260926/
Good point. Remote controlled or robot cars might make a difference. Especially with trucks. The problem is that the people who create the traffic problems the dangerous drivers won’t use that technology. My guess is what we will see is a lot of robot trucks or buses on the road with drivers sitting in them to make the public happy. That’s what happened at a lot of robotic rail systems. The Green Line light rail in LA could run without operators but it doesn’t. It’ll take several years. Still even robot cars need a road to run on. If the freeway is jammed by gridlock the robot car wouldn’t be much good.