Tim Heitman/USA TODAY Sports

Coming off his career year, DeMarco Murray will be an unrestricted free agent this offseason.

Now that the Super Bowl has passed, it's time to turn our attention to the offseason, and free agency.

Dallas Cowboys running back DeMarco Murray had an incredible 2014 season, rushing for nearly 500 more yards than any other NFL player. But as an unrestricted free agent coming off a career year, Murray could be looking to cash in while the Cowboys have other priorities, including locking up Dez Bryant, who is also an unrestricted free agent.

Cowboys owner Jerry Jones has said it will be "a challenge" to sign both Murray and Bryant, and a quick look at the Cowboys' 2015 salary cap shows why. Dallas currently is projected about $5 million under the cap for 2015, but as ESPN's Todd Archer outlined here, the Cowboys can create about $45 million in cap space to sign both Murray and Bryant. So what should they do?

Below are some thoughts on why it might be wise to let Murray walk.

Running backs have become devalued

In recent years, running backs have been devalued more and more by NFL teams. Consider:

• Fewer top draft picks: No running back has been drafted in the first round in either of the past two NFL drafts. Those are the only two years in the Common Draft Era (since 1967) when that has happened.

• Lower spending: In 2014, NFL teams spent five percent of the salary cap on running backs, the lowest percentage in the past 15 seasons. Teams spent almost nine percent of the cap on quarterbacks, the second-highest percentage over that span. From 2000 to 2004, teams spent nearly the same on running backs as quarterbacks (seven percent of the cap).

• More running back by committee approaches: In each of the past two seasons, only two running backs have had at least 300 carries (including Murray in 2014). In the previous 15 seasons, an average of 7.9 running backs per season had at least 300 rushes.

Murray due for decline?

Murray had 449 touches in 2014, the sixth most in a season in NFL history. It was also the first season of his career he played in 16 games. History indicates regression will win out next season and his production will decline.

RBs With 400 Touches In Single Season*

NFL History

Murray's season was the 42nd instance in NFL history of a player having at least 400 touches (rushes plus receptions) in a season.

Here's how the previous 41 fared the following season:

• 35 (85 percent) had fewer touches (averaged 106.4 fewer touches)

• 33 (81 percent) had fewer yards from scrimmage (averaged 590 fewer yards from scrimmage)

• 25 (61 percent) averaged fewer yards per touch (0.22 fewer yards per touch)

• 25 (61 percent) had fewer total touchdowns (3.3 fewer touchdowns)

• 20 (49 percent) of them played in fewer games (averaged 2.3 fewer games)

Cowboys have internal options

Joseph Randle and Ryan Williams (who spent the season on the practice squad) are the only running backs on the Cowboys' active roster signed for 2015.

Murray vs. Other Cowboys RBs

2014 Per-Rush Averages

The team could also elect to bring back Lance Dunbar, who is a restricted free agent.

Murray led the league in rushing, but how much was due to him and how much was due to the Cowboys' offensive line?

Randle and Dunbar combined actually had a higher per-rush average than Murray did this past season, albeit with a much smaller workload.

In fact, among the 73 running backs with at least 50 rushes in 2014, nobody averaged more yards per rush than Randle (6.7).