HIGHWAY NOISE MEASUREMENT, SIMULATION, AND MIXED REACTIONS

TWO MAJOR STUDIES FORMED THE BASIS FOR A THEORY OF TRAFFIC NOISE FROM WHICH A SIMULATION MODEL WAS BUILT, AND COMPUTERS WERE USED TO DESCRIBE THE NOISE OF DIFFERENT HIGHWAY SITUATIONS. THE TWO STUDIES BASIC TO THE SIMULATION MODEL INVOLVED COMPARING VARIOUS MEASURES OF SOUND, AND DECIDING UPON A SIMPLE, YET SATISFACTORY PHYSICAL MEASURE OF THE LEVEL OF SOUND, AND THEN MEASURING NOISE PRODUCED BY VARIOUS KINDS AND CLASSES OF VEHICLES. THE PHYSICAL MEASURE OF NOISE, SOUND LEVEL IN DECIBELS AS MEASURED ON THE A SCALE OF A STANDARD SOUND LEVEL METER, WAS SELECTED AS BEING STATISTICALLY INDISTINGUISHABLE FROM THE BEST PSYCHOLOGICALLY DERIVED MEASURES IN ITS RELIABILITY AS A PREDICTOR OF HUMAN RESPONSE TO VEHICLE NOISE. THE NOISE LEVEL RESULTS DESCRIBED ARE EXPRESSED IN TERMS OF THIS MEASURE, COMMONLY REFERRED TO AS DBA. IN ADDITION TO THE MODEL, A DETAILED INTERVIEW WAS CONDUCTED WITH PEOPLE LIVING RELATIVELY NEAR A FREEWAY OR HIGHWAY. THESE INTERVIEWS FORM THE BASIS FOR PREDICTIONS ABOUT RESIDENTS' EXPRESSED ANNOYANCE WITH NOISE. NOISE FROM INDIVIDUAL MOTOR VEHICLES HAS TWO MAJOR COMPONENTS: ENGINE-EXHAUST, AND TIRE-ROADWAY INTERACTION. MOST MODERN PASSENGER CARS GENERATE AS MUCH NOISE BY TIRE-ROADWAY INTERACTION AS BY ENGINE-EXHAUST UNDER NORMAL OPERATING CONDITIONS. ACCELERATION, HOWEVER, PRODUCES MORE ENGINE-EXHAUST NOISE. LARGE DIESEL TRUCKS, SIGNIFICANTLY NOISIER THAN CARS, HOWEVER, REPRESENT A RELATIVELY SMALL PROPORTION OF TOTAL TRAFFIC ON URBAN HIGHWAYS. A LARGE DIESEL TRUCK-TRAILER COMBINATION IS EXPECTED TO PRODUCE 10 TO 15 DB HIGHER NOISE LEVELS THAN A PASSENGER CAR AT THE SAME ROAD SPEED DUE TO THE RELATIVE CONTACT AREAS OF THE TIRES WITH THE ROAD. INDICATIONS ARE THAT ATTEMPTS TO CONTROL VEHICLE NOISE BY OBJECTIVE NOISE LEVEL LEGISLATION HAVE NOT BEEN HIGHLY SUCCESSFUL. THE CONTROL OF NOISE THROUGH HIGHWAY PLANNING IS MORE LIKELY TO BE FRUITFUL THAN IS ENFORCEMENT OF VEHICLE LEVEL. SPECIFIC GUIDES ARE SET FORTH THAT WILL HELP STATE HIGHWAY DEPARTMENT ENGINEERS DETERMINE THE MOST APPROPRIATE MEANS AND UNITS FOR MEASURING AND EVALUATING HIGHWAY NOISE FOR A NUMBER OF COMMON TRAFFIC SITUATIONS. THESE GUIDES ARE PRESENTED IN TABULAR AND GRAPHIC FORM. THEY ARE SUPPLEMENTED BY A COMPUTER SIMULATION MODEL THAT ALLOWS THE ENGINEER TO PREDICT UNDER FIXED CONDITIONS OF VEHICLE SPEED, TRUCK MIX, VEHICULAR VOLUME, AND DISTANCE FROM THE HIGHWAY, THE VEHICLE NOISE LEVELS FOR ANY EXISTING OR PLANNING HIGHWAY SITUATION FOR FREELY FLOWING TRAFFIC.