STAMFORD, Conn. -

Prices fell by two percent in the lanes last month, with some segments seeing rates drop by over 4 percent from 2013 levels.

And back in September, used-vehicle prices, after adjusting for MSRP, fell by 0.6 percent from August and 2.7 percent year-over-year, according to the latest RVI Risk Outlook report.

What factors are contributing to this decline?

RVI says lease penetration continues to grow and is expected to increase for 2014 and 2015 model year vehicles, which will lead to more off-lease supply in coming years — but there are other contributing factors, as well.

In fact, the new-car market is having a direct impact on used prices.

“Greater incentives activity, a more competitive new-vehicle market, and an increase in the supply of used vehicles will contribute to a drop in used-vehicle prices,” RVI analysts said.

In September, average incentive rates reached 16 percent of MSRP, which helped push new-vehicle sales to a SAAR of 16.34 million units. Impressive incentives may have also pushed more consumers into the leasing market, as well, since during Q2, leasing penetration rates came in at 19 percent of total new-vehicles sales, according to the RVI report.

Leasing penetration grew the most during the first half of the year for the Mini brand, with rates growing to 33 percent compared to 22 percent during the first six months of 2013. On the other hand, Land Rover saw the greatest drop in leasing interest, with penetration falling from 34 percent in the first half of 2013 to 22 percent during the same period of this year.

RVI analysts predict the upturn in the U.S. economy as well as the increase in new-vehicle sales will contribute to growth in the supply of used vehicles over the next few years.

The U.S. economy grew at an annual rate of 3.5 percent during the third quarter and continues to improve, albeit on a gradual scale.

“Competition among manufacturers and incentives activity is also expected to increase,” in coming years, RVI analysts pointed out.

With this in mind, RVI predicts used-vehicles prices to fall by 10 percent by 2017 with used rates expected to continue dropping next year.

To get a handle on just how much used supply is increasing, take a look at the compact vehicle segment. Price drops in this fuel-efficient segment have been more dramatic than those seen in the overall market. In September, prices for the segment fell by 2 percent year-over-year and 5.3 percent from August rates. And during the same month, the supply of used compact cars was up by 15 percent from September 2013.

RVI predicts this number to continue to grow, and expects prices for the compact segment to drop by 8.6 percent by 2017.

Part of the short-term trend seen in the compact market may be, in part, due to gas price declines, which have just fallen below $3.