Citywide Traffic Engineering
Washington, DC - 2017



  • Traffic Operations and Analysis,
  • Traffic Engineering Design
  • Signal Timing Optimization



Sabra & Associates, Inc. (SAI) is the lead consultant for two DDOT A/E contracts for citywide signal timing optimization and traffic system analyses.


Traffic Signal Optimization
SWA is optimizing all 1,600+ signalized intersections within the District of Columbia. The work includes development, field implementation and fine tuning of optimized signal timing plans for 5 patterns (AM, Midday, PM, Nighttime and Weekend) in the City’s 170 controllers and QuicNet Central System software; Synchro and SimTraffic modeling; vehicular, pedestrian and bicycle traffic data collection; Before and After GPS-based Travel time and delay studies; geometric inventory of each intersection, Traffic operations analyses at congested intersections, including developing recommendations, and at-times developing work-order plans for geometric modifications, turn restrictions, signing, phasing changes, and traffic signal modifications; Signal controller firmware conversion from Bi-Tran 215 Interval to 233 Phase; design and update of all 1,600 TS Drawings and Dial Sheets; Development of Manuals, Standard Procedures, and Guidelines for DDOT Traffic Signal (TS) Drawings, Dial Sheets (signal timing), and vehicular and pedestrian clearance interval calculations;  Design and management of an on-line GIS database of signalized intersection information including traffic counts and signal timings for data sharing; Software development to automate phase-assignment, distance measurements, calculations, and records for clearance intervals analysis and update of all Y, AR, W and FDW clearance intervals to meet 2009 MUTCD standards.  Challenges included the quick optimization and evaluation of 120 intersections along critical commuter corridors to meet high-priority needs, signal timing at circles, squares and complex intersections with complex phasing with multiple overlaps, extensions, at closed-spaced intersections with multiple controllers, increasing pedestrian Walk and FDW times while at the same time decreasing congestion and keeping the cycle lengths low; field implementation of signal timing plans. “Before” and “After” studies of the work completed to date (300 intersections) have shown considerable benefits to drivers, bus riders and pedestrians. Vehicle travel times were reduced by an average of 13%; delays reduced by over 30% and the number of stops reduced by 25%. Analysis of metro bus stop data showed that the number of buses running behind schedule decreased by over 40%.

Traffic Operations & Analysis
SWA has performed 30+ studies including congested intersection, intersection safety, corridor studies, bicycle analysis, pedestrian safety and signal warrant studies. The signal warrant analyses include new vehicle, pedestrian or pedestrian-hybrid beacons (HAWK signals).  Work efforts include: Collection of traffic data including vehicles, bus, bicycle and pedestrians; Roadway capacity and level of service analysis; Review of crash data to identify crash patterns and contributing factors and correlate them to physical or operational deficiencies; Perform field observations of risky behaviors; Measure vehicle queues, delays and speeds; Evaluate the need for new or upgraded traffic control devices per the criteria set forth in the Manual on Uniform Traffic Control Devices; Assess signal system operations with new traffic signals; Identification of safety countermeasures and recommendations to improve traffic operations; Development of concept plans and costs.

7055 Samuel Morse Dr., Ste. 100
Columbia, MD 21046
443-741-3500 | F: 443-741-3700

2018 Sabra & Associates, Inc. | All rights reserved | Contact us