In classical mechanics, linear momentum is the product of the mass and velocity of an object. So when a big object like heavy truck moving quickly it will has a large momentum.
Momentum: P= m*Δv
where, Δv = Velocity Change, m = Mass, P = Momentum Change.
For example, when the mass i 30000kg, the Δv is 9m/s, Then momentum is 270000 kg-m/s.