You can select more than one road by holding down the Ctrl key while clicking on each road in turn.
If you edit the details for multiple roads, the dialog box shows the common values for the select roads. If all the roads are from the same city, that city name will be displayed. If all the roads are two way, then the Two-way option will be selected.
If the road properties are different, then the displayed value will be blank. If you leave it blank, the setting for each road will not change. This allows you to, for example, change the city name for many roads, while leaving their street name or directionality unchanged.
There is one exception. If you select different road types, the road type value will also be blank. But Cartouche treats a blank road type as a Street. If you save your changes all the roads will change to streets. This is not a problem if you select roads of all the same type. You can also go back and change roads to their correct type.