This is an older question but things have changed. Its a common misconception on what the contribution cap is. A few things.
In 2014, the IRS did not adjust the maximum contribution from the previous year which include 401(k) accounts, 403(b) accounts, most 457 plans, and Thrift Savings Plans, will be $18,000, up $500 from $17,500.
Savers and investors aged 50 or older can take advantage of a catch-up contribution. In 2015, taxpayers who meet this age-based criterion can contribute an additional $6,000 above the regular maximum of $18,000, thus you can contribute a maximum of $24,000 into these tax-advantaged accounts.
The total contribution limit, including employer contributions, has increased to $53,000
You can actually contribute up to 53k (including matching) so the exact amount you contribute from your actual income may end up being more or less than 24k. If you get a poor employer match you can actually contribute more but it would go in as after tax dollars and not claim the tax deduction. Note: after tax does NOT equal Roth.
However if your a high salaried individual you can use this as a potential loop hole for funding a Roth IRA. Chances are if your making enough money to contribute 53k Total Contributions then your not going to qualify for a roth. However once you retire (or possibly before depending on the plan withdraw terms) you can roll the after tax money into a Roth IRA. This is a gray area on the tax policy. The IRS may come back and change their mind about this. If considering this option talk to a tax adviser.