The accident happened at 12:43 a.m. Thursday in the eastbound lanes of Kirkwood Highway east of Duncan Road.
According to investigators, the victim, said to be a Hispanic man between the ages of 35 and 40 years old, was attempting to cross the roadway, heading northbound, when he stepped into the path of the Trooper's fully marked 2007 Ford Crown Victoria patrol vehicle.
The 32-year-old Trooper attempted swerve to avoid the man, but the left front corner of the patrol vehicle struck the pedestrian.
The victim was transported to the Christiana Hospital Trauma Center in critical condition.
The preliminary investigation revealed that the pedestrian attempted to cross the roadway outside of a designated and marked crosswalk. In addition, both alcohol and drugs were found to have been a factor on the part of the pedestrian.
The Trooper was uninjured in the incident.