SMALL-CAR SPEEDS AND SPACINGS ON URBAN EXPRESSWAYS

GENERAL DATA ON SMALL-CAR SPEEDS AND THEIR EFFECT ON HIGHWAY CAPACITY ARE PROVIDED. FOUR LOCATIONS WERE SELECTED IN THE WASHINGTON METROPOLITAN AREA ON FOUR LANE DIVIDED FACILITIES OF EXPRESSWAY-TYPE DESIGN, EACH WITH A DIFFERENT CHARACTER AND COMPOSITION OF TRAFFIC AND EACH SERVING COMMUTER TRAFFIC DURING THE PEAK PERIODS. THEY ARE /1/ THE WASHINGTON-BALTIMORE PARKWAY AT THE DISTRICT OF COLUMBIA LINE, BUILT IN 1955, WITH A 45 MPH SPEED LIMIT, /2/ SHIRLEY HIGHWAY BETWEEN RIDGE AND GLEBE ROADS IN ARLINGTON, COMPLETED IN WORLD WAR II, WITH A 50 MPH SPEED LIMIT FOR PASSENGER CARS AND 45 MPH FOR TRUCKS, /3/ MT. VERNON MEMORIAL HIGHWAY BETWEEN THE ENTRANCES TO WASHINGTON NATIONAL AIRPORT, CONSTRUCTED BEFORE 1940, A MAJOR ARTERIAL LINK BETWEEN D.C. AND ALEXANDRIA, VA., WITH A 40 MPH SPEED LIMIT AT THE STUDY LOCATION, AND /4/ SUITLAND PARKWAY, EAST OF ALABAMA AVENUE, TO DETERMINE THE EFFECT OF GRADE, AN ARTERIAL BETWEEN D.C. AND GOVERNMENT INSTALLATIONS IN PRINCE GEORGES COUNTY, WITH A 45 MPH SPEED LIMIT FOR PASSENGER CARS. THE TOTAL SAMPLE FOR EACH OF THE FIRST THREE LOCATIONS WAS 7000, 6500, AND 3200 VEHICLES RESPECTIVELY, 12 PERCENT BEING FOREIGN AND COMPACT CARS. THE AVERAGE SPEEDS OBTAINED AT THE THE TANGENT LOCATIONS BY VEHICLE TYPE, TIME PERIOD, VOLUME RATE, AND LANE ARE GIVEN. AVERAGE SPEEDS BY VEHICLE TYPE ARE COMPARED FOR THE THREE LOCATIONS WITH INSIGNIFICANT GRADES BASED ON A SAMPLE OF ABOUT 40 PERCENT OF THE STANDARD CARS AND ALL COMPACT AND FOREIGN CARS. THE AVERAGE SPEED OBTAINED AT THE GRADE LOCATION BY LANE, STATION, TIME PERIOD, AND TYPE OF VEHICLE ARE GIVEN AND SPEEDS ARE COMPARED BY VEHICLE TYPE. SPACING VALUES ARE CALCULATED. THERE APPEARS TO BE NO SIGNIFICANT DIFFERENCE IN SPEED OR CONSISTENT TREND TOWARD A HIGHER OR LOWER SPEED FOR COMPACT OR FOREIGN CARS AS COMPARED TO STANDARD AMERICAN PASSENGER CARS AT ANY OF THE LOCATIONS NOR IS THERE DIFFERENCE BETWEEN THEM AS MEASURED BY THEIR SPACING. THESE STUDIES WERE LIMITED TO URBAN EXPRESSWAYS. POSSIBLY, WHERE CONSIDERATION IS GIVEN TO THE EFFECT OF THE SMALL CARS ON CITY STREETS AND ON OPEN RURAL HIGHWAYS WHERE THE AVERAGE SPEED MORE NEARLY APPROACHES THE SPEED CAPABILITIES OF THE SMALL CARS, FURTHER RESEARCH COULD YIELD VALUABLE INFORMATION FOR THE DETERMINATION OF THE OVER-ALL INFLUENCE OF SMALL CARS ON DRIVER BEHAVIOR.