INFLUENCE OF INCIDENTS ON FREEWAY QUALITY OF SERVICE

DISABLED VEHICLES IN MOVING TRAFFIC HAVE A SIGNIFICANT EFFECT ON FREEWAY OPERATIONS, PARTICULARLY DURING PEAK PERIODS. THIS REPORT QUANTIFIES, FOR THE GULF FREEWAY IN HOUSTON, THE IMPACT ON OPERATIONS BY RELATING FREQUENCY, DURATION, AND FLOW PASSING FREEWAY INCIDENTS. DATA WERE COLLECTED FOR WEEKDAYS ONLY DURING DAYLIGHT HOURS BY UTILIZING THE 6 1/2-MILE COVERAGE OF THE GULF FREEWAY TELEVISION SURVEILLANCE SYSTEM. DURING A 2-YEAR PERIOD, 1,154 ACCIDENTS AND 1,11- STALLS IN MOVING LANES WERE OBSERVED. IT WAS FOUND THAT THE AVERAGE ACCIDENT REQUIRED 19 MIN FROM THE TIME OF REPORTING TO REMOVAL FROM TRAFFIC LANES AND AN ADDITIONAL 26 MIN FOR POLICE INVESTIGATION. STALLED VEHICLES WERE REMOVED WITHIN 18 MIN AFTER BEING REPORTED TO THE POLICE. ONE-MINUTE TRAFFIC VOLUMES WERE MEASURED FOR NORMAL CONDITIONS AND AT BOTTLENECKS CREATED BY INCIDENTS. THE STUDY SECTION HAS 3 LANES IN EACH DIRECTION OF TRAVEL WITH A NORMAL DIRECTIONAL PEAK-PERIOD FLOW OF 5,560 VEHICLES PER HOUR. IT WAS FOUND THAT INCIDENTS CREATED A REDUCTON IN FLOW DISPROPORTIONATE TO THE PHYSICAL REDUCTION IN ROADWAY WIDTH. THE AVERAGE FLOW RATE WAS 2,750 VEHICLES PER HOUR WITH 1 LANE BLOCKED BY AN ACCIDENT; 2,880, WITH 1 LANE BLOCKED BY A STALLED VEHICLE; 4,030, WITH AN ACCIDENT ON THE SHOULDER; AND 1,150, WITH 2 LANES BLOCKED BY AN ACCIDENT. DELAY FOR HYPOTHETICAL MORNING PEAK-PERIOD INCIDENTS ARE PRESENTED TO ILLUSTRATE THE MAGNITUDE OF MOTORIST DELAY. A STALLED VEHICLE CAUSED A DELAY OF 1,610 VEHICLE-HOURS, WHILE THE 1-LANE ACCIDENT AND 2-LANE ACCIDENT CAUSED DELAYS OF 2,940 AND 4,620 VEHICLE-HOURS RESPECTIVELY. /AUTHOR/