The following tables list the major categories of property and equipment, as well as the weighted-average estimated useful life for each category (in years):


Millions, except estimated useful life As of June 30, 2025	Cost		Accumulated depreciation		Net book value		Estimated useful life
Land	$	5,450	N/A		$	5,450	N/A
Road:
Rail and other track material	19,515		7,797		11,718		45
Ties	12,593		4,206		8,387		34
Ballast	6,575		2,245		4,330		34
Other roadway [a]	24,202		5,897		18,305		47
Total road	62,885		20,145		42,740		N/A
Equipment:
Locomotives	9,793		3,799		5,994		18
Freight cars	3,077		1,073		2,004		23
Work equipment and other	1,273		515		758		17
Total equipment	14,143		5,387		8,756		N/A
Technology and other	1,390		624		766		12
Construction in progress	1,305		N/A		1,305		N/A
Total	$	85,173	$	26,156	$	59,017	N/A


Millions, except estimated useful life As of December 31, 2024	Cost		Accumulated depreciation		Net book value		Estimated useful life
Land	$	5,441	N/A		$	5,441	N/A
Road:
Rail and other track material	19,283		7,642		11,641		46
Ties	12,358		4,109		8,249		34
Ballast	6,495		2,182		4,313		34
Other roadway [a]	23,913		5,681		18,232		47
Total road	62,049		19,614		42,435		N/A
Equipment:
Locomotives	9,517		3,724		5,793		18
Freight cars	3,011		1,037		1,974		22
Work equipment and other [b]	1,222		482		740		17
Total equipment	13,750		5,243		8,507		N/A
Technology and other	1,431		640		791		12
Construction in progress	1,169		N/A		1,169		N/A
Total	$	83,840	$	25,497	$	58,343	N/A

[b]For retirements of depreciable railroad properties that do not occur in the normal course of business, a gain or loss may be recognized if the retirement meets each of the following three conditions: (a) is unusual, (b) is material in amount, and (c) varies significantly from the retirement profile identified through our depreciation studies. In the second quarter of 2024, we sold a large portion of an intermodal equipment asset class resulting in a $46 million gain recognized in other expense in our Condensed Consolidated Statements of Income.