Congress faces thorny issues, deadlines WASHINGTON, June 18 (UPI) -- Substantive and politically touchy issues concerning student loans and highway construction face lawmakers when they return to Washington this week. Unless Congress acts, the interest rate on federal student loans will double from 3.4 percent to 6.8 percent and a short-term measure funding the nation's highway- and bridge-building program will expire July 1. Members of Congress have two weeks to fashion legislation on both issues, or face potential voter wrath in November, observers said. A conference committee of Senate and House members has been negotiating for weeks to develop compromise legislation on a $109 billion two-year highway funding bill, The Washington Post reported Sunday. One roadblock is whether the bill would include language that has been included in House measures that would require the White House to approve construction of the Keystone XL oil pipeline in Nebraska. Concerning federal student loan interest rates, lawmakers haven't been able to reach agreement despite urgings by President Obama to freeze interest rates for another year. Presumptive Republican presidential nominee Mitt Romney has said he concurs with the freeze, as has Senate Majority Leader Harry Reid and House Speaker John Boehner. Leaders can't agree on how to pay for the nearly $6 billion price tag. The Republican-held House passed a bill that would pay for the freeze by cutting the healthcare reform effort, a bill that died in the Senate. A Democratic alternative that would close a payroll tax loophole for some wealthier small business executives also was blocked in the Senate.