SPECIAL PROBLEMS IN THE ANALYSIS OF URBAN EXPRESSWAY PROJECTS

WHEN TRAFFIC IS ASSIGNED TO THE FREEWAY ALL THE THEORETICAL FORMULAS UTILIZE TIME SAVINGS AS A CRITERION FOR DECIDING WHAT PERCENTAGE TO ASSIGN. HOWEVER, TIME IS VALUED DIFFERENTLY BY DIFFERENT PERSONS. THE PROBLEM IS STILL PRESENT EVEN IF ALL THE ALTERNATES CALL FOR MORE THAN 50% USAGE WHICH ON THE CALIFORNIA SCALE MEANS THAT THE USERS SAVE MONEY. USING A FIXED VALUE FOR TIME, IT IS FOUND THAT THE NON-USERS LOSE MONEY MORE ON SOME ALTERNATES THAN ON OTHERS. FIVE RANDOMLY SELECTED CASES ARE CITED WHICH IN PURE THEORY DID NOT NECESSARILY GIVE THE RIGHT ANSWERS. ONE CASE CITED IS THE MOST FREQUENTLY ENCOUNTERED PROBLEM IN DECIDING HOW MUCH IS THE DIFFERENCE IN USES BETWEEN ALTERNATES WHETHER IT IS OWING TO THE REAL DIFFERENCE BETWEEN THE ALTERNATES AND TRAFFIC SERVICE OR HOW MUCH IS OWING TO THE UNAVOIDABLE ERROR OF ESTIMATE. ANOTHER CASE IS CITED TO SHOW THE HAZARDS OF USING THE BENEFIT RATIO AS A CRITERION. THE DIFFICULTY IN SELECTING ALTERNATES MAY BE DUE TO THE FACT THAT THERE IS NO ACCURATE ORIGIN AND DESTINATION SURVEY OR ZONAL EXPANSION SYSTEM, AND THAT THIS SEGMENT IN A LARGE NETWORK OF ROADS IS TOO SMALL TO ARRIVE AT A COMMON TRAFFIC VOLUME. FIVE ALTERNATES ARE PRESENTED IN ANOTHER SECTION OF A LARGE METROPOLITAN COMMUNITY. FOUR OF THESE ALTERNATES APPROXIMATE THE ALIGNMENT OF THE EXISTING HIGHWAY, BUT THE FIFTH CREATES A NEW DIAGONAL. THE DIAGONAL LINE SHOWS CONSIDERABLY MORE BENEFITS THAN THE ONES WHICH MORE-OR-LESS PARALLEL THE EXISTING MAIN HIGHWAY. IT SHOULD BE NOTED THAT ANY TIME A DIAGONAL IS IMPOSED ON A GRID NETWORK IT WILL SHORTEN THE DISTANCE FOR MANY USERS OF THE FACILITY WITHOUT LENGTHENING THE DISTANCE FOR NON-USERS. ANOTHER CASE SHOWS A SEGMENT OF EXISTING FREEWAY AND ITS CONNECTIONS TO THE CITY STREET SYSTEM. THERE IS GREAT CONTROVERSEY AMONG DESIGN AND PLANNING ENGINEERS ABOUT THE SPACING OF RAMPS, BUT IT IS EASILY SEEN THAT IF BENEFITS ARE COMPUTED ON THE BASIS OF TIME AND DISTANCE SAVINGS FOR ROAD USERS, THERE WOULD BE ALMOST NO LIMIT TO THE NUMBER OF RAMPS THAT SHOULD BE PROVIDED. THE VALUE OF TIME IS DISCUSSED BY MANY OF THE DISCUSSERS.

Media Info

  • Monograph Title: ECONOMIC ANALYSIS IN HIGHWAY PROGRAMMING, LOCATION AND DESIGN: WORKSHOP CONFERENCE PROCEEDINGS, SEPTEMBER 17, 1959
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00201824
  • Record Type: Publication
  • Files: TRIS, TRB
  • Created Date: Aug 26 1970 12:00AM