can't distinguish between droplets or flakes and obstacles on the road

Cars aren't driven in the rain or snow as detection

Staff and visitors at Google's California campus were given a treat this week as the company took its driverless car prototype for a spin.

The technology is still undergoing tests, and the firm hasn't announced when exactly the vehicles will become an addition to public roads because engineers are still ironing out a number of issues.

But, that hasn't stopped the project's director Chris Urmson and his team demonstrating its potential to fans in Mountain View.

Staff and visitors at Google's California campus were given a treat this week as the company showed off its driverless car prototype (pictured). The technology is still undergoing tests, and the firm hasn't announced when the vehicles will become common place on our roads as engineers are still ironing out issues

Mr Urmson is also hopeful the cars will be roadworthy within the next five years.

One of the features said to be delaying the car's release is its inability to cope in heavy rain or snow.

An insider told MIT Technology Review that the current prototype cars are very reliant on maps to navigate and can’t react like a human driver, dodging potholes and other hazards.

The latest official figures from Google revealed the cars have already driven themselves for more 700,000 miles (1,126,540km), but they struggle to cope in snowy conditions and can't negotiate heavy rain.

Mr Urmson said this is because the detection technology is not yet strong enough to separate certain objects from weather conditions.

While the cars’ cameras can spot a traffic light changing, they can be confused by strong sunlight.

They don’t distinguish between an empty plastic bag - which could be easily driven over - or a rock, so cars must drive around both. They also can’t detect uncovered manholes or potholes.

Mr Urmson said: ‘I could construct a construction zone that could befuddle the car.’

HOW DOES GOOGLE'S AUTONOMOUS CAR WORK? This graphic reveals how Google's prototype driverless car looks and works. The car makes turns and reacts to vehicles and pedestrians based on computer programs that predict what others might do, and data from sensors including radar and cameras that read, in real-time, what other objects are actually doing The prototype two-seater cars have buttons to autonomously begin and end the drive. The car makes turns and reacts to vehicles and pedestrians based on computer programs that predict what others might do, and data from sensors including radar and cameras that read, in real-time, what other objects are actually doing. The route might be set by typing a destination into a map or using spoken commands according to Chris Urmson, the leader of Google's self-driving car team. The car will be powered by electricity and could go about 100 miles (160 km) before charging. Its shape suggests a rounded-out Volkswagen Beetle - something that might move people around a corporate campus or congested downtown - with headlights and sensors arrayed to resemble a friendly face. The front of the vehicle has a soft foam-like material where a traditional bumper would be and a more flexible windscreen, in a bid to be safer for pedestrians. In these prototypes speed is restricted to 25mph (40 km/h) and the ability to self-drive will depend on specifically designed Google road maps tested on the company’s current fleet of vehicles. Ultimately the vehicles will be faster and will be able to use Google's extended maps service. Driving works by using GPS technology to locate the vehicle’s exact position on an electronic map. A combination of radar, lasers and cameras sitting on top of the roof give the car a 360-degree ‘view’, with sensors linked to computer software able to ‘see’ and identify people, cars, road signs and markings and traffic lights. Advertisement

The cars ‘see’ pedestrians as moving blocks of pixels and know to stop, but unlike a cautious human driver, they could not spot a traffic policeman at the side of the road, waving for traffic to stop - which could lead to trouble.

Despite the cars being allowed on public roads, they need to prepare to set off in more detail than a human driver, because a precise map must be created of exactly where to go – and a car cannot deviate from its route.

An area has to be mapped multiple times by a sensor vehicle to record details such as driveways, in order to make the cars' routes.

These details then need to be pored over metre-by metre by humans and computers, in a much more labour-intensive process than in needed to maker Google Maps.

One of the features said to be delaying the car's (pictured) release is its inability to cope in heavy rain or snow. An insider recently admitted that the current prototype cars are very reliant on maps to navigate and can’t react like a human driver, dodging potholes and other hazards. They also struggle in poor weather conditions

Despite best efforts, routes can lack details such as temporary traffic lights that have been installed, or if there are road works or potholes to avoid, which the car might drive over.

LAW CHANGES TO SUIT DRIVERLESS VEHICLES AROUND THE WORLD In the US, driverless cars are only allowed on roads in certain states if someone sits in the driver's seat. The California Department of Motor Vehicles is expected to start granting licences to certain driverless cars and their human co-pilots as soon as this month. Changes to the United Nations Convention on Road Traffic, which dates back to 1968, are also afoot. It used to state: 'Every driver shall at all times be able to control his vehicle or to guide his animals.' An amendment agreed in May would allow a car to drive itself, as long as the system 'can be overridden or switched off by the driver'. A driver must be present and able to take the wheel at any time. The convention covers European countries, Mexico, Chile, Brazil and Russia, although not the United States, Japan or China. Advertisement

In addition, maps have only been made for a few thousand miles of road, so in order for the cars to roam the US, Google would need to pour a vast amount of resources into mapping the rest of the vast country, down to the tiniest changing detail.

The company is working on ironing out all these problems. For example, if a Google car notes new lights and street signs, it sends a message to update the mapping software.

Google unveiled a compact version of its car without a steering wheel, but it will now have to re-introduce the wheel to comply with the California Department of Motor Vehicles’ new regulations.

Despite all these set-backs, Mr Urmson said autonomous cars will ‘happen more quickly than people think’ – perhaps as soon as in five years’ time.

Last month, Google was awarded 25 of the first 29 permits issued by the state of California to test driverless cars on public roads.

Each permit costs $150 for the first vehicle, plus $50 for each additional vehicle, and each one must be insured for up to $5 million.

Self-driving cars have been undergoing private tests for at least three years, but government legislation requires permits for them to be used on public roads.

The first licence for an autonomous vehicle was issued by Nevada in March 2012 to a Toyota Prius that Google modified to include its driverless technology.

Google tests its cars virually (pictured) as well as on real roads. Google’s cars have driven themselves over 700,000 miles (1,126,540km) - but there is still a long way to go to hone the technology