Safety and consumer advocates want state lawmakers to put the brakes on a bipartisan measure that could allow 75 mph speed limits on some highways and also boost speeds on other roads.   Representatives from the National Safety Council and the Consumer Federation of the Southeast, and others say higher speed limits will make roads less safe as drivers will continue to travel faster than the posted speed limit.  State Senators Jeff Brandes  and Jeff Clemens, say their legislative proposal is only to allow the DOT to determine if limits should be raised 5 miles per hour on certain roads.