From the orvietoviva.com web site.....
Orvieto Parking
There are several visitor parking options in the center of Orvieto: street parking and public parking lots.
Street Parking
Street parking in Orvieto is very common and visitor spots are outlined with blue lines. These spots are “pay parking only” and the rates are Euro 1.50 per hour (rates are subject to change and may vary per area).
Parking Lots
Here is a list of the main parking lots in Orvieto. You must pay at the grey parking ticket machines and they are usually located on the side of the parking lots.
Campo della Fiera – ex Foro Boario – This parking lot is located near the old Medieval Aqueduct and is one of the largest parking areas in the city. The lot can be accessed from the Strada Statale or the Umbro-Casentinese Road Conce. This parking area also has a covered garage with direct access to the center of the city by the elevator and the mechanic escalators located at the path, or Via Ripa Medici. Both methods lead to the side of Orvieto near Piazza della Repubblica.
The elevator Ripa Medici is free and open until 12.00 Pm while the mechanic escalators are open until 9.00 pm. The parking fee of campo della Fiera is Euro 1.50/hour.
Via Roma Parking – In front of the former barracks there is also a near completion, large covered pay parking lot.
Piazza Marconi – Piazza Marconi has many visitor parking spaces and is located directly behind Piazza Duomo, Piazza XXIX Marzo and Piazza del Popolo. This parking lot has a mix of visitor and resident parking so be sure to only park in spaces outlined in blue. The visitor parking is a fee of Euro 1.50/hour rates are subject to change and may vary per lot).
Piazza Cahen – This parking lot has a mix of free and payment parking . The visitor parking is a fee of Euro 1.50/hour rates are subject to change and may vary per lot).