D.C. police are trying to identify a good samaritan who was struck and killed by a cement truck Wednesday afternoon while trying to help direct traffic for a tractor-trailer that was too tall for the Third Street Tunnel.

The driver of the 18-wheeler realized that his vehicle exceeded the clearance height of the tunnel and tried to turn around at the 400 block of New York Avenue Northwest at about 4:30 p.m., police said. A pedestrian tried to help the driver by directing traffic.