4.3.4.1. Unity of Use.The key question in determining the larger parcel is whether parcels have an integrated use.364 To meet the unity of use test in federal acquisitions, the lands in question must have the same or an integrated highest and best use.365 Lands with dissimilar uses are not part of the same larger parcel, and must be considered as separate and distinct tracts for compensation and valuation purposes.366

As with any other aspect of the highest and best use analysis, actual use is compelling evidence of highest and best use.367 An integrated use that is merely planned or hoped for is not sufficient to meet the unity of use test.368 In determining the larger parcel, a potential use “may be weighed only if there is a ‘reasonable probability’ the lands in question will be put to that use in the reasonably near future.”369 Even then, “potential use is only one factor to consider in determination of the ‘unity’ issue, along with unity of ownership, contiguity, and existing use.”370 

The federal unity of use test turns on an integrated highest and best use. But some courts have invoked a different unity of use test (rarely applicable in federal acquisitions) to determine whether to allow separate valuations of property taken and of damage to property not taken371—loosely, and misleadingly, called severance damage.372 This taking plus damages compensation formula, also known as the State Rule, is generally improper in federal acquisitions regardless of unity of use.373 Still, based on the State Rule measure of compensation, courts have required proof of actual unitary use with the part taken to allow consideration of separately calculated severance damage to a landowner’s other property.374 The actual unitary use test reflects the requirement that compensation cannot be charged for damage to separate and independent parcels belonging to the same owner as the property taken.375 Under the Federal Rule, compensation in partial acquisitions is measured by the difference in the market value of the landowner’s property before and after the government’s acquisition, as discussed in Section 4.6. Using this federal measure, “there is no occasion for the making of any special award or determination of ‘severance damage,’ because the matter is included in the finding of what the remainder of the land was worth immediately after the taking.”376 For this reason, severance damage “concepts have no application” to acquisitions that are subject to “a before-and-after valuation . . . .”377 With no separate calculation of severance damage under the Federal Rule, actual unitary use is not determinative, but merely a factor to be considered in determining the larger parcel in federal acquisitions.378 For a full discussion of the Federal Rule, the State Rule, appropriate treatment of damages and benefits, and other issues arising in partial acquisitions, see Section 4.6. 

In federal acquisitions, whether under the Federal Rule or (with appropriate legal instructions) the State Rule, the ultimate goal is to fairly measure the owner’s actual compensable loss.379 As a result, “strict proof of the loss in market value to the remaining parcel is obligatory.”380 Similarly, the availability of replacement property for the part acquired must be considered, as reasonable buyers and sellers would do.381