Both the Quad and Quint are trucks that combine functions of different trucks. The only real difference is how many functions they can perform.
The Quad combines four functions into one truck. It has a water tank and pumping capabilities and carries ground ladders and hoses. These go back as far as 1925 but are losing popularity now. Most departments are going to a Quint.
By Bidgee (Own work) [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)%5D, via Wikimedia Commons
As you may have figured out, The Quint combines five functions into one truck. As well as the different functions combined into a quad, the Quint also features an aerial ladder. There may be many reasons for going to the Quint. But, one of the main ones is staff shortages. This is especially true for volunteer departments(which I’ll be going into more about on Saturday). The optimal number for a safe and effective crew on a truck or engine is at least four firefighters. With staff shortages(and a declining number of volunteers), it’s easier to outfit a quint with a full crew than a truck and an engine.