Performing traffic engineering tasks which include but not limited to managing, reducing & utilizing traffic data, signal timing plans, traffic analysis, traffic impact studies, parking studies, bus routes & transit studies, signage, control, and traffic operations, etc. SI Engineering, P.C. (SIE) is a full-service consulting engineering firm headquartered in downtown Manhattan with an office in Princeton, NJ providing services in civil, structural, transportation engineering, bridge & facility inspection, construction management & inspection and lighting design.