Ordinarily, the good ways from Hanoi to Halong Bay is around 170 km. Transport Bus takes you around 3.5 hours, included haft-hour for break time from Hanoi to Halong Bay. On the off chance that you pass by private vehicle, it takes around 3 hours.
Then again, there is another course which just takes you about 2.5 hours for going to Halong Bay. You can contract a vehicle or purchase a ticket of a VIP transport to go from Hanoi downtown area to Halong Bay through the new Hanoi – Hai Phong interstate, which abbreviates the separation between Hanoi – Halong to about more than 150km.
In any case, there will be an expense for the new expressway which is about 6.5 USD/turn/vehicle and that is the motivation behind why the cost for transportation through this new course is somewhat higher than the bygone one.
You can peruse more detail how to make a Best Halong Bay Day Tour From Hanoi here