2 . Car companies such as Tesla and Nissan have been leading the way in electric car technology. What makes these car “green” is that because they run on electricity instead of gas, they do not give off any polluting greenhouse gases. The Toyota Mirai is also a kind of green car, since it is powered by a hydrogen fuel battery(氢燃料电池).

Hydrogen, as you know, exists in large quantities on the earth. It was used to power gaslights for centuries before electric lights came along. Hydrogen fuel can be made from many sources including water, natural gas and even rubbish. As for energy contained, 9.5kg of hydrogen is similar to 25kg of gas. According to Toyota, the two tanks on the Mirai hold 5kg of hydrogen, and can cover a distance of over 300 miles. This is twice the output of gas cars.

In a hydrogen fuel battery, the one proton (质子)and one electron in a hydrogen atom(原子) are broken up. While the electrons power the car, the hydrogen protons work with the oxygen atom to produce water. At the same time, it also produces a lot of heat which turns this water into water vapor. This is the reason why cars running on hydrogen fuel batteries give off water vapor from their exhaust pipes when running.

According to Toyota, it takes only 5 minutes to refill a hydrogen tank, which is much quicker than charging (充电) electric cars. However, the biggest difficulty for the company is the availability of hydrogen-charging stations. California and the New England states are in the process of building a hydrogen superhighway—with charging stations along the way. Countries like Germany, Japan and UK are also adding more charging stations.

The Toyota Mirai will be available in the U.S. in the second half of 2015 for $ 58,000. This hydrogen-fueled car will probably take the place of gas cars in the near future. After all, it is an energy-saving and environment-friendly car.

3 . Transport News

Light rail service closure

From 7.30 pm Friday 8 to 1 am Monday 11 October, L2 Randwick Line and L3 Kingsford Line light rail services will not run between Circular Quay and Central Chalmers Street, due to maintenance (保养) works. You can use other transport including trains or walking.

Ferry service closure

From Monday 6 September, F9 Watsons Bay Sydney Ferries services will not be stopping at Watsons Bay Wharf which will be receiving maintenance. The wharf (码头) should reopen to Sydney Ferry services from Saturday 18 September. A replacement bus service will run between Watsons Bay and Rose Bay wharves for the closing period.

Bus stop changes

From Monday 30 August, there will be some bus stop changes in order to complete construction work of the Bondi Junction Cycleway. A number of bus stops will be closed to provide convenience for construction work on Oxford Street from Monday 30 August to the end of November.

For more information on the Bondi Junction Cycleway project please visit the construction page on Waverley Council’s website.

Minor train timetable changes

On Saturday 12 June, some minor timetable changes are being made to train services. These changes are being introduced as part of a regular review of train services to help improve network reliability.

You can plan your new trip using the Trip Planner to see if your travel is affected by the changes. You can also check transport apps, indicator screens on platforms or listen for announcements at stations.

I’m so glad to read about the changes talking place in your city. It’s really good news that you can travel by subway in Xi’an, though there’s only one line there. Here in London we have twelve lines. By the way, we don’t use the word “subway” here. It’s American English. We call it “the Underground”, instead.

The London Underground is very famous. It’s famous for several reasons. First of all, part of the underground railway today is the oldest in the world, which opened in 1863. Secondly, the London Underground is also the first line to have electric trains, in 1890. Thirdly but not the last, the London Underground is the second largest metro system in the world, after the Shanghai Metro. There are 270 stations in the Underground and it has 402 kilometres of tracks (轨道). What’s more, the city of London itself helps make the transportation system famous! I’ve got a few photos to help you build a clear picture of the Underground in my city. They are together with this mail.

In your email, you also said workers were building more lines. I’m sure your city is developing fast. Maybe you can send me a few photos of your city today. I really want to see the changes taking place there. I’m happy for you to live there in an ancient city with such a new look!

So much for now. I’ll write soon again. Best wishes!

6 . There’s a continuing controversy over whether electric vehicles should produce sounds to let the blind and other pedestrians know they’re on the scene. Some think those sounds should be standardized—like the “beep, beep, beep” of heavy machinery backing up, so you’ll think “something heavy is coming this way” when you hear it — and some think any sound will do.       

This is a serious subject. Plug-in hybrid cars (电混动力车) and battery electric vehicles are super-quiet, and a study at the University of California, Riverside concludes that people listening to recordings on headphones can hear a regular gas car coming from 28 feet away, but a hybrid in battery mode only when it’s 7 feet away.

In response, the European Union has put new rules into play: all new electric vehicle models must have a sound-producing device, which sounds like a traditional engine. Starting in 2021, all new electric vehicles of any model will need the Acoustic Vehicle Alerting System or AVAS. That sound will come into play when the car is traveling backwards or when it’s traveling at less than 12 miles an hour — speeds at which cars are more likely to be mixing with pedestrians.     

That’s a nice start, say representatives for the blind, but more is needed. “We’re calling on the government to take this announcement further by requiring AVAS on all existing electric and hybrid vehicles and ensuring drivers have them switched on,” John Welsman, guide dog owner and Guide Dogs staff member, said in a statement.

Drivers in most cases have the ability to shut off the device when needed. My guess is that they will eventually be standardized so your mind will automatically register “electric car” when you hear it. And that’s probably a good thing to reduce the mayhem (混乱) on the roads.

8 . Flight security rules are changing almost daily; however, there have been two main changes which seem likely to remain.

The first change is that international passengers flying to the USA are getting a pat-down at the gate. In some places this is being taken very seriously with a thorough check, but in many places the checks are cursory (粗略的) as people don’t think it contributes much to safety.

The second change is that the USA is increasing the number of air marshals (空警) on flights to, from and within their country. Action by passengers, whether security personnel or other flyers, is now seen as the most effective improvement in flight security since 9/11.

But it is likely that moves announced in 2010 to remove the liquids carry-on restrictions will be quietly dropped for political reasons.

No matter how well prepared a traveler is before a trip, there is a chance that security rules will change at the last minute or during travel. For example, for three days over Christmas last year those flying from other countries to the USA were not allowed out of their seats for the last hour of the flight. Some people flying in August found they were unable to carry on any bags after the liquid bomb attempt.

There are things passengers can do to save trouble:

 Before heading to the airport, check the rules posted on the airline’s website.

 Reduce the amount of baggage being carried on board, and especially the items in your pockets. Fewer items mean it’s easier to pass through security-quicker bag checks, less time needed to empty pockets at the metal detector.

 Allow more time between connecting flights and before departure.

 If you’ll have trouble standing in a queue for an extended period of time then arrange with your airline in advance for wheelchair assistance.

 Pick the fast-moving security lines — normally the ones filled with business travelers move fastest.