URBAN TRAVEL TIME

Abstract

THIS PAPER UTILIZES THE CONCEPT OF URBAN VELOCITY FIELDS TO DERIVE A RELATIVELY SIMPLE PROCEDURE FOR OBTAINING GOOD ESTIMATES OF TRAVEL TIMES BETWEEN DIFFERENT LOCATIONS IN URBAN AREAS. THE PROCEDURE DOES NOT MAKE USE OF ANY SHORTEST ROUTE ALGORITHMS BASED ON A NETWORK VIEW OF THE URBAN TRANSPORTATION SYSTEM. IT IS ASSUMED THAT ROAD NETWORKS IN CITIES ARE SUFFICIENTLY DENSE TO ADMIT THE VIEW THAT URBAN TRAVEL TAKES PLACE ON A CONTINUOUS TERRAIN, WHERE VELOCITIES OF TRAVEL VARY ONLY AS A FUNCTION OF DISTANCE FROM THE CITY CENTER. A VELOCITY FIELD FOR EACH CITY IS THUS OBTAINED AND MINIMUM TIME PATHS CONSTRUCTED AS CURVED PATHS. THREE INTERRELATED METHODS OF CALCULATING TRAVEL TIME ON SUCH ROUTES ARE DISCUSSED. THE FIRST METHOD DESCRIBES AN ANALYTIC PROCEDURE FOR CALCULATING TRAVEL TIME BETWEEN TWO POINTS ON AN ARBITRARY VELOCITY FIELD. THE SECOND METHOD UTILIZES A TRANSFORMATION OF THE URBAN PLANE INTO A TIME SURFACE ON WHICH DISTANCE CORRESPONDS TO TRAVEL TIME. THE THIRD METHOD IS A GRAPHICAL CONSTRUCTION, WHICH MAKES POSSIBLE A MANUAL CALCULATION OF TRAVEL TIME. THE LATTER IS USED TO COMPUTE TRAVEL TIMES BETWEEN ZONE CENTROIDS USED IN THE SELNEC (SOUTH EAST LANCASHIRE-NORTH EAST CHESHIRE) TRANSPORTATION STUDY. THE ESTIMATES OBTAINED BY THIS METHOD ARE COMPARED WITH THE SELNEC ESTIMATES AND SHOW A GOOD FIT. /TRRL/

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