The terms you are using are somewhat taken out of context so I do not know exactly how they are used. With that said, let me explain the two words "Voluntary" refers to coverage provided to a customer because the insurer wants to provide coverage in that state for the assigned price. You are free to buy it or not and the company is free to insure you or not."Involuntary" would refer to policies an insurer must write, because of some risk sharing mechanism such as an Assigned Risk Plan. The insurer by virtue of its voluntary writings is then required to take some per cent of the involuntary exposures in a state. This is true of assigned risk plans which operate in about 40 states.
"Excess" refers to an amount of coverage over some other coverage. You can obtain Excess coverage over your limits of liability coverage and sometimes over your Uninsured Motorist Coverage. Typically a person might buy an Umbrella policy to be "excess"of their personal auto coverage. If you are offered Excess coverage over a specific coverage you should ask an insurance professional if an umbrella is available as well.
"Excess" refers to an amount of coverage over some other coverage. You can obtain Excess coverage over your limits of liability coverage and sometimes over your Uninsured Motorist Coverage. Typically a person might buy an Umbrella policy to be "excess"of their personal auto coverage. If you are offered Excess coverage over a specific coverage you should ask an insurance professional if an umbrella is available as well.