Plane is (expensive) way to travel.
the most expensive
Traveling on foot is (difficult) way.
the most difficult
The old trolleybus is (dangerous) among all transport.
the most dangerous
A plane is (fast) than a train.
faster
A taxi (small) form of public transport.
the smallest
The boat is (slow) than the ship.
slower
The underground is (cheap) than a taxi.
cheaper
A car is (comfortable) than a tram.
more comfortable