Perhaps coming up against the difficult year-over-year comparison analysts noticed on the new-car side, TrueCar is projecting a slight softening in used-vehicle sales this month.

TrueCar forecasted that March’s total used sales, including turns at franchised and independent dealerships as well as private-party transactions, may exceed 3,581,085, which would be down 0.9 percent compared with March of last year.

Meanwhile, the firm projected the pace of March new-model sales should expand to a seasonally adjusted annualized rate (SAAR) of 16.9 million new units on continued strong consumer demand even with one less weekend than a year ago and harsh weather conditions across the country.

TrueCar contends new-vehicle sales, including fleet, should reach 1,524,700 units for the month, down 0.8 percent from a year ago. Adjusting for one less selling day compared with March of last year, deliveries should rise 3.1 percent on a daily selling rate (DSR) basis, while the SAAR is up from 16.5 million.

Eric Lyman, vice president of industry insights for TrueCar, described factors that might be impacting new-vehicle showroom traffic, but they may as well be influencing potential buyers of used vehicles, too.

"Spring has officially sprung, but much of the country is still pushing away snow piled up at the doorstep,” Lyman said.

“Given what a strong month last March was, this slight decline in total volume isn't surprising,” he continued. “We’re bullish on the retail outlook for the second half of the year and the industry remains on track to reach TrueCar's 17 million-unit projection for 2015.”

TrueCar also mentioned the new-vehicle sales expansion, on pace to rise for a sixth consecutive year, coincides with improving economic indicators including GDP, housing starts, the Dow Jones Industrial Average and wages and salaries, all of which are projected to strengthen in 2015.

Similarly, new home sales reached a seven-year high in February while the Consumer Price Index edged up 0.2 percent after three straight months of declines, according to analysts.

TrueCar went on to note Subaru may be the biggest gainer in new-model sales, followed by Honda and Toyota, with respective increases of 10.6 percent, 4.5 percent and 4.2 percent.

Analysts added FCA and its Chrysler, Jeep, Dodge, Ram and Fiat brands, should report a 1.3 percent gain even compared with strong volume registered a year ago. This forecast should result in 60 consecutive months of year-over-year of sales gains for FCA.

Lyman closed by sharing that incentive spending by automakers averaged $2,691 per vehicle in March, down 1.3 percent from a year ago and up 0.4 percent above February.

“It’s positive that incentives aren't rising from the year-ago level,” Lyman said. “This and steady demand for light trucks means automakers can expect continued revenue gains.”