Traffic Engineering What? Why? How?

TRAFFIC ENGINEERING WHAT? WHY? HOW? ARIZONA HIGHWAY DEPARTMENT TRAFFIC ENGINEERING DIVISION ARIZONA HIGHWAY COMMISSION Forrest C. Braden Chairman Bus Mead Vice-Chairman Ed C. Locklear Member Peter B. WiJharm Member Dan C. McKinney Member Justin Herman State Highway Director William N. Price State Highway Engineer David L. Kennison Acting Traffic Civil Engineer Ronald D. Midkiff Traffic Designer February 1968 l-ITHO~"APHED BY ARIZONA HIG~"AY OEPARTMENT REPRODuCTION DIV"i'ON TABLE OF CONTENTS Pllge . 1 Why is Traffic Engineering Essential? ... , ..... 2 How Does the Traffic Engineer Solve Traffic Problems? 3 What is Trattic Engineering? How Does the Traffic Engineer Promote Safer Traffic Operation? ,..... 4 5 What are Traffic Control Devices? . What is Meant by Uniformity of Traffic Control Devices? 6 How are Speed Limits Determined? .... 8 .. What Effect Do Posted Speed Limits Have on Actual Traffic Speeds? " 9 When Should Traffic Signals Be Installed? 10 What is the Primary Purpose of Guide Signs? . . 12 How are Guide Sign Messages Determined? 14 Is Angle Curb Parking a Vanishing Custom? 16 What Do Arizona Laws Say About Angle Parking? 18 Why Parallel Curb Parking? 19 Does Prohibition of All Curb Parking Help Traffic Movement? .... .. .. .. .. .. .. . . ... . 20 WHAT IS TRAFFIC ENGINEERING? Traffic Engineering is the application of engineering principles to achieve safe, efficient, and convenient traffic operation. Traffic Engineering deals with the movement of motor vehicles and the methods used to direct them to their destination. From a scientific standpoint, traffic engineer- ingapplies the physical laws of motion to the motor vehicle, the roadway, and the driver, while bring- ing into playa knowledge of psychology and the habits of the motoring public. -1- WHY IS TRAFFIC ENGINEERING ESSENTIAL? HOW DOES THE TRAFFIC ENGINEER SOLVE TRAFFIC PROBLEMS? Many persons still wonder why a traffic prob- The role of the traffic engineer may be com- lem is so difficult that an engineer should be called pared to that of the medical profession in protect- upon for a solution. Why not just install a traffic ing the public. As a trained professional he looks signal, or lower the speed limit, or erect more atthe symptoms. and in order to make a competent signs? diagnosis he makes traffic counts, analyzes acci- One of the greatest obstacles a professional dent statistics, studies speed data, examines road- traffic engineer faces in applying sound principles way conditions, conducts research, and studies of traffic engineering is the fact that "everyone is what other professionais are doing and the results a traffic expert!" The unfortunate result of this they have achieved, attitude of expertise is the creation of traffic haz- ards when false theories of individuals or groups are put into effect. Just as the doctor's decision is accepted in matters regarding health. even though the medi- Whenever unnecessary or excessive traffic cine may be bitter or the needle painful, so should controls are installed, hazardous traffic conditions the decision of the professional t