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				Accumulated		Net Book		Estimated
As of December 31, 2014		Cost		Depreciation		Value		Useful Life
Land		$	5,194	$	N/A	$	5,194	N/A
Road:
Rail and other track material			14,588		5,241		9,347	33
Ties			9,102		2,450		6,652	33
Ballast			4,826		1,264		3,562	34
Other roadway [a]			16,476		2,852		13,624	47
Total road			44,992		11,807		33,185	N/A
Equipment:
Locomotives			8,276		3,694		4,582	20
Freight cars			2,116		968		1,148	25
Work equipment and other			684		153		531	18
Total equipment			11,076		4,815		6,261	N/A
Technology and other			872		320		552	10
Construction in progress			1,080		-		1,080	N/A
Total		$	63,214	$	16,942	$	46,272	N/A

[a]	Other roadway includes grading, bridges and tunnels, signals, buildings, and other road assets.

Millions, Except Estimated Useful Life				Accumulated		Net Book		Estimated
As of December 31, 2013		Cost		Depreciation		Value		Useful Life
Land		$	5,120	$	N/A	$	5,120	N/A
Road:
Rail and other track material			13,861		4,970		8,891	35
Ties			8,785		2,310		6,475	33
Ballast			4,621		1,171		3,450	34
Other roadway [a]			15,596		2,726		12,870	48
Total road			42,863		11,177		31,686	N/A
Equipment:
Locomotives			7,518		3,481		4,037	20
Freight cars			2,085		1,000		1,085	25
Work equipment and other			561		119		442	18
Total equipment			10,164		4,600		5,564	N/A
Technology and other			711		286		425	10
Construction in progress			954		-		954	N/A
Total		$	59,812	$	16,063	$	43,749	N/A

[a]	Other roadway includes grading, bridges and tunnels, signals, buildings, and other road assets.