Mobile lane closures, which are increasingly used, are a potentially hazardous traffic control procedure for highway maintenance and operations activities. To improve the safety of workers and motorists, Applied Research Associates, Inc., studied driver behavior around full-scale field tests of mobile lane closures. Tests were conducted over a range of traffic, roadway, and driver conditions, and effects of various traffic control components (including truck number, spacing, and configuration; sign messages; and police presence) were evaluated. This report summarizes Phase I results and important findings regarding the behavior of motorists around mobile lane closures. Phase II research is ongoing and will recommend revisions to existing traffic control standards.