Discuss the ideas expressed by these two engineers suggesting their solution of public transport development in modern cities.

David: The population in cities is expected to double in the next 20 years. It is a challenge for public transport and a lack of high-quality transport will make such areas the realm of the private car, so the metro might become the preferred choice to improve urban mobility.

Michael: When demand goes up, the first thing to do is add more services. While passenger numbers are increasing, I believe the metro is the most viable solution, because it is the only mode that can cope efficiently with huge flows of people, and make public transport attractive, successful and viable.

David: The latter is strategically important because only rail can compete effectively with cars on journey time and reliability, while buses are usually slower than cars because they stop frequently in addition to being caught in traffic jams. Besides oil and petrol prices are rising rather rapidly.

Michael: Yes and when planning new metro lines we must consider several factors if we want to compete effectively with cars. Speed and regularity of trains must out perform that of cars. High frequency must offset the advantage of the immediate availability of a car.

David: But a fast journey time will not be sufficient to entice people out of their automobiles. People must get the feeling of being somewhere they want to be.Our biggest challenge is that we don’t go everywhere our passengers want to go.

Michael: This is why it is vital to build a network in the cities, where most journeys are by car, and to show people what the metro is like and how easy it is to use. Environmental concerns over noise and air pollution will be overcome and may provide a cost-effective alternative and a real solution for city authorities.

David: Right, but building the metro through a busy city is a challenge too, because of the need to minimize disruption to road traffic. The top-down construction of underground station boxes and TBMs operating might be other challenges.

Michael: To build a world-class metro means to look for the most efficient solutions, from a technological point of view, and mastery of state-of-the-art technology.

David: Of course, but rail does not come cheap, and it will remain too expensive for many cities even if such cities are crying out for rail transit.But I want to point out that some of the world’s most successful metros were built at times when the cities such as Mexico City and Seoul were not very wealthy.

Michael: Yes, investment in rail is always heavy, but there is also considerable interest in sustainable and environmentally friendly public transport in modern cities.