Both. 그럼 basically means :"then"or "so" and It also can be used as a positive reply, for example -Are you coming? -Of course!/Definitely!(그럼) ,but it can be used as well when somenone's leaving "I should get going now.." /"그럼..."

"This coffee is too hot to drink".It emphasizes that you can't drink it 'cause it's hot. Otherwise you can use similar phrases "This coffee is still too hot.I can't drink it" etc.

Correction/Proposal :

My answer:
Long time ago,distance usually led to communication difficulties.As time went by, transportation improved a lot making it  more convenient for people to chat,work and have fun from up close.However, the amount of cars increased daily.As a result,more problems appeared.The traffic jam,almost happening every single morning,caused many troubles.In order to solve them,some scientists proposed lots of ideas.The greatest one was having railways made.
Roads get ruined a lot by car accidents and natural disasters,instead of railways,which have a minimal chance of having a train crush.That of course,make the railways more popular than roads. Moreover, some people probably can't afford bying a car.If they use the train though ,they just need to pay some money for the ticket and will not worry about the traffic jam.Thus,not only does it shorten the distance between people but it also makes the communication easier.
As far as I am concerned,government should spend money on railways rather than roads.Meanwhile,trains also protect the environment because they move by electricity rather than fuel.And there will be less risk of having an accident which can put the passengers at ease.

Hope I was helpful :)