Many aftermarket retailers have been flourishing due to aging vehicles on the roads in the U.S. The average age of vehicles on U.S. roads is at an all time high of 11.4 years, up from 11.2 years and 10.9 years in 2012 and 2010, respectively. Moreover, vehicles older than 12 years or more have increased by 20%. Aging vehicles are creating pent-up demand for aftermarket parts and services, helping aftermarket retailers and service providers record strong gains.

The do-it-for-me, or DIFM, market is hot and it is increasing at four times the pace of the do-it-yourself, or DIY, market . Investors can benefit from each of these segments. Monro Muffler Brake (MNRO -0.54%) caters to the DIFM and services segment, while Pep Boys-Manny, Moe & Jack (NYSE: PBY) is a hybrid of DIFM-DIY. These two are entirely different from an auto parts aftermarket retailer like Advance Auto Parts (AAP 1.93%).

Who has the best prospects?

What's Monro up to?
Monro Muffler reported sales and net income growth of 16% and 18%, respectively, in its latest quarter. In management's own assessment, the top-line performance was disappointing as a result of a weak retail environment during the quarter, which negatively influenced purchasing behavior.

Monro Muffler has been aggressively making acquisitions so it is in a good position to benefit when spending increases. It recently closed a deal to buy Curry's Auto Service's 10 stores and it is also negotiating with seven other takeover prospects. The acquisition will increase its store count to 945 . Out of this, 400 are tire-centric stores, making Monro the third largest "independent" tire retailer in the U.S.

Last year, Monro acquired Ken Towery's Tire & Auto Service (27 stores); Enger Auto Service & Tires (11 stores); Tire King Complete Car Care (nine stores); Tire Barn Warehouse of Anderson (31 stores); and 17 Tuffy Muffler/Car-X locations in Wisconsin and South Carolina . These acquisitions have enabled Monro to record impressive top and bottom-line growth apart from allowing the company to increase its geographical coverage.

For the full fiscal year, Monro expects total sales in the range of $830 million-$845 million. This takes into consideration the impact of acquisitions in 2013 and 2014 and comparable-store sales in the range of minus 1% to flat versus last year. Monro expects earnings per share in the range of $1.58-$1.65, which represents a 20%-25% increase versus fiscal 2013.

Pep Boys' strategies also look good
Pep Boys' operations are based on the DIFM-DIY hybrid model, where 80% of revenue comes from DIFM and services. Pep Boys has also been acquiring businesses to grow its footprint. For example, it recently purchased 17 Discount Tire Centers from AKH Company. Consequently, at least one Pep Boys location will now be within a three-mile reach of almost three-fourths of Los Angeles' population .

In addition, Pep Boys is also introducing a new store format design to make customer engagement and servicing more streamlined. The new format is also intended to make the stores appealing to women and achieve Pep Boys' goal of being the best alternative to the dealer .

Besides catering to the automotive replacement parts and accessory industry, Pep Boys also provides non-automotive merchandise such as generators, power tools, and personal transportation products. This adds an element of diversity compared to Monro.

Advance Auto: The biggest player
Advance Auto has also been aggressively expanding its presence both through acquisitions and new store openings. The acquisition of BWP Distributors this year added 124 stores to its network. On the back of this acquisition and new store openings, revenue surged by 4.3% versus the year-ago period to $1.5 billion in the third quarter .

Recently, Advance Auto announced the acquisition of GPII, as a result of which it has become the largest automotive aftermarket provider in North America. GPII operates under the CARQUEST and WORLDPAC brands. After the deal was announced, the share price shot up considerably which signified investor confidence. After the acquisition, Advance Auto will be the leader in automotive aftermarket parts with over 70,000 team members and a balanced blend of DIY, commercial, and e-commerce business-to-business operations.

Takeaway
All three companies have been taking to acquisitions to grow their businesses. The good thing is that they operate in different areas of the auto parts industry, which means that investors have three good options at their disposal to benefit from aging cars in the U.S.

If you're looking for the cheapest option of the three, Advance Auto would be a good bet. If it is growth that you are after, Monro's aggressive acquisition strategy should satisfy your taste. Finally, if you're interested in something balanced, Pep Boys, with a hybrid business model, is the way to go.