According to Caddell, reasons for the year's record numbers included the improving economy, reduced unemployment rates, lower fuel prices, low interest rates and continued strong dealer incentives.

CO-OP Member Center noted one credit union made so many auto loans that it was "loaned out" and ended up launching a loan participation program to sell some of its loans.

In addition, 2015 was also a big year for leasing, with 27% of new autos being leased; many consumers chose to lease in order to upgrade to luxury and/or larger-sized cars and trucks, according to CO-OP Member Center.

However, because sales and leases of new vehicles were so strong in 2015, the year was not particularly big for used vehicle sales.

"The industry had a record year in auto sales, and Northwest was no exception," said Jeff Bentley, senior vice president and chief lending officer for the $3 billion, Herndon, Va.-based Northwest Federal Credit Union, said. "We saw a strong increase in loans for both new and used cars, buoyed by offers like our Car Show and Sale special rate of 1.25% with no payments for 90 days. We recognized that auto sales would be a key part of a strong, solid growth plan for 2015, and our on-site car shows throughout the year made it convenient for members to find and finance cars through Northwest."

The Madison, Wis.-based, $2.3 billion Summit Credit Union also had a strong year in auto lending in 2015, according to Penny Armagost, vice president of lending, analytics and credit risk.

"We offer both direct and indirect auto loan programs, and 2015 was a great year for us, with an 8% increase in indirect auto loans over the previous year," she said.

While it may be too early to tell what impact the Federal Reserve interest rate increase will have on auto sales, CO-OP Member Center said it expects 2016 to be another good year, estimating 17.2 million vehicle sales during the year (just 200,000 fewer than in 2015). One sign boding well for 2016 was that auto sales held steady in November and December of 2015, which are traditionally slow times of year.

Why does CO-OP Member Center expect 2016 to be another good year? First, even though the Fed announced an interest rate increase, lending rates are low, terms remain attractive, and it is expected these rates and terms will extend into 2016 – assuming that the Fed doesn't increase rates again in the coming term. Second, gas prices continue to remain low. Third, a large consumer inventory of older cars that need to be replaced remains. Finally, auto manufacturers are bringing a number of new products onto the market, including more electric vehicles and other models that offer more efficient mileage.

CO-OP Member Center noted, however, that while 2016 is expected to be strong, it is not expected to be as strong as 2015 for several reasons. For one, the demand for new vehicles will slightly soften, given the large number of sales in 2015. In addition, lending rates are projected to increase slightly.

"Rates could really affect sales if they go up once or twice during the year," Caddell said.

Credit unions specifically are expected to benefit from the continued strength into 2016, according to CO-OP Member Center. One reason behind this prediction is most credit unions offer 84-month terms at 4% to 5% interest, which leads to relatively low monthly payments.

"Consequently, we don't see many credit unions increasing their auto lending rates in response to increases by the Fed, because the current lending market is so strong," Carol Cline-Parton, vice president of CO-OP Member Center, said.

Bentley and Armagost both expressed great optimism about their auto lending programs in 2016.

"We expect 2016 to mirror 2015, and expect to see a continued new interest in auto loans, matching 2015′s numbers," Bentley said. "Even with the recent rate increase, Northwest offers very competitive rates and a level of service that the credit union industry is known for."

Armagost noted, "We are hoping 2016 will be even better for us than 2015. In fact, we have added a staff member on the indirect side, so we can have even more face time and visits with dealers. We will also be able to increase our turnaround times for their requests."

According to CO-OP Member Center, some larger credit unions may increase rates in 2016, simply because they can. In fact, it reported, one large credit union increased its rate by 0.25%, in step with the Fed increase.

"However, most credit unions will probably maintain current rates in order to stay competitive," CO-OP Member Center stated in a news release. "For example, we saw fewer interest rate changes by credit unions in 2015 than ever before in our records."