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PROPERTY, PLANT AND EQUIPMENT (Notes)
12 Months Ended
Dec. 31, 2017
Property, Plant and Equipment [Line Items]  
PROPERTY, PLANT AND EQUIPMENT
9.
PROPERTY, PLANT AND EQUIPMENT

The following table sets forth our property, plant and equipment by property type, for the periods indicated:
 
 
December 31,
 
December 31,
 
 
2017
 
2016
 
 
(Thousands of dollars)
Natural gas distribution pipelines and related equipment
 
$
4,572,343

 
$
4,321,429

Natural gas transmission pipelines and related equipment
 
497,791

 
481,953

General plant and other
 
513,445

 
530,459

Construction work in process
 
130,333

 
70,327

Property, plant and equipment
 
5,713,912

 
5,404,168

Accumulated depreciation and amortization
 
(1,706,327
)
 
(1,672,548
)
Net property, plant and equipment
 
$
4,007,585

 
$
3,731,620



We compute depreciation expense by applying composite, straight-line rates of 2.0 percent to 3.0 percent that were approved by various regulatory authorities.

We recorded capitalized interest of $3.0 million, $3.6 million and $2.6 million for the years ended December 31, 2017, 2016 and 2015, respectively. We incurred liabilities for construction work in process and asset removal costs that had not been paid at December 31, 2017, 2016 and 2015 of $21.7 million, $11.9 million and $15.0 million, respectively. Such amounts are not included in capital expenditures on our Consolidated Statements of Cash Flows.