Interest expense of $102.2 million was $3.5 million higher compared to the same period in 2015. The increase in interest expense was due primarily to the refund liability relating to the ROE complaints and higher borrowing levels to finance capital investments.
The effective income tax rate for the six months ended June 30, 2016 was 38.6 percent compared to 37.5 percent for the same period in 2015.
Year-to-Date 2016 Financial Results Detail — Non-GAAP Measures
ITC's adjusted operating revenues for the six months ended June 30, 2016 increased to $603.9 million compared to $568.4 million from the same period last year. Amounts reported for the six months ended June 30, 2016 and 2015 exclude approximately $25.7 million and $20.8 million, respectively, in reduced pre-tax revenues associated with the base ROE refund liability. This increase was primarily due to higher revenue requirements attributable to a higher rate base at our regulated operating subsidiaries, as well as an increase in regional cost sharing revenues resulting from additional capital projects being placed in-service that have been identified by MISO and SPP as eligible for regional cost sharing partially offset by the election of bonus depreciation.
O&M expenses of $52.2 million were $3.4 million lower for the six months ended June 30, 2016 compared to the same period in 2015. The decrease in O&M expenses was primarily due to lower vegetation management requirements.
G&A expenses of $66.7 million were $5.2 million lower compared to the same period in 2015. Amounts reported for the six months ended June 30, 2016 exclude approximately $28.5 million of pre-tax expenses related to the Fortis transaction and the six months ended June 30, 2015 exclude approximately $1.5 million of pre-tax expenses related to regulatory charges. The decrease in G&A expenses was primarily due to lower incentive-based compensation for bonus payments.
Depreciation and amortization expenses of $78.2 million increased by $8.2 million for the six months ended June 30, 2016 compared to the same period in 2015 due to a higher depreciable base resulting from property, plant and equipment in- service additions.
Taxes other than income taxes of $45.7 million were $4.5 million higher compared to the same period in 2015. Amounts reported for the six months ended June 30, 2016 exclude approximately $0.1 million of pre-tax expenses associated with the Fortis transaction. This increase was due to 2015 capital additions at our regulated operating subsidiaries, which are included in the assessment for 2016 personal property taxes.
Interest expense of $99.0 million was $1.2 million higher compared to the same period in 2015. Amounts reported for the six months ended June 30, 2016 and 2015 exclude approximately $3.2 million and $0.9 million, respectively, of pre-tax expenses associated with the adjustments to operating earnings noted previously. The increase in interest expense was due primarily to higher borrowing levels to finance capital investments.
The effective income tax rate for the six months ended June 30, 2016 was 37.6 percent compared to 37.5 percent for the same period in 2015. Amounts reported for the six months ended June 30, 2016 and 2015 exclude income taxes of $19.4 million and $8.8 million, respectively, associated with adjustments to operating earnings noted previously.
Other Available Information
More detail about second quarter 2016 results may be found in ITC's Form 10-Q filing. Once filed with the Securities and Exchange Commission, an electronic copy of our 10-Q can be found at our website, http://investor.itc-holdings.com. Paper copies can also be made available by contacting us through our website.
About ITC Holdings Corp.
ITC Holdings Corp. (NYSE: ITC) is the nation's largest independent electric transmission company. Based in Novi, Michigan, ITC invests in the electric transmission grid to improve reliability, expand access to markets, lower the overall cost of delivered energy and allow new generating resources to interconnect to its transmission systems. Through its regulated operating subsidiaries ITCTransmission, Michigan Electric Transmission Company, ITC Midwest and ITC Great Plains, ITC owns and operates high-voltage transmission facilities in Michigan , Iowa, Minnesota, Illinois, Missouri, Kansas and Oklahoma, serving a combined peak load exceeding 26,000 megawatts along approximately 15,700 circuit miles of transmission line. ITC's grid development focus includes growth through regulated infrastructure investment as well as domestic and international expansion through merchant and other commercial development opportunities. For more information, please visit ITC's website at www.itc-holdings.com (ITC-itc-F).