Traffic Engineering – Traffic Control Devices

Traffic Engineering Textbook

Traffic Engineering Book is ideal for a one/two-semester undergraduate survey, and/or for graduate courses on Traffic Engineering, Highway Capacity Analysis, and Traffic Control and Operations.


Traffic control devices are signs, signals, markings or other devices used to regulate, warn or guide highway traffic. When properly used they promote safe orderly and convenient movement of traffic, both motorized and non-motorized. All necessary devices should be in place on any highway open to traffic.

Uniformity of traffic control devices and their application enables highway users to quickly recognize and interpret devices and to react correctly to them. Uniformity means treating similar situations in the same way. Effective traffic control devices meet five basic requirements. They fulfill a need; command attention; convey a clear, simple meaning; command the respect of road users; and give adequate time for proper response.

The application of traffic control devices should be based on sound engineering principles in conjunction with studies of traffic flow, accidents, speeds, delays, and physical conditions. Once a determination has been made, the devices used must conform to the Manual of Uniform Traffic Control Devices.


Signs are essential to inform highway users of specific regulations and to call attention to hazards that are not self-evident. They also inform drivers about highway routes, directions, destinations, and points of interest. When considering the need for warning or guide signs, the needs of highway users unfamiliar with the area should be a major consideration.

Traffic signs are standardized in terms of shape, color, legend and symbols to enable highway uses to quickly and correctly comprehend the sign message.  There are some signs that do not follow these basic shapes and colors. For example, the STOP sign (Regulatory) is an octagon shape with a white legend on a red background.

Standard signs are specified in a variety of sizes to provide suitable target value and legibility for each type highway environment and condition. Sign size is identified by a letter (usually A, B, C, D, or E).

The minimum height of a roadside sign (difference in elevation between the edge of the roadway and the bottom of the sign) on conventional highways and expressways is seven feet. Where there are multiple signs on the same support, the lowest sign should be at least six feet. At locations where it is considered unlikely that signs would interfere with pedestrians or be blocked by parked vehicles, these minimum heights are reduced to five feet and four feet respectively.


Regulatory signs inform highway users of traffic regulations. They are sometimes used to advise of statutory rules which may not be apparent or which require emphasis. Unlike regulations, however, statutory rules are in effect even if not posted.

Stop and Yield signs may be used to assign right of way at intersections. Sight distance across the corners of the intersection and the prevailing approach speed on the major highway are significant in determining whether a Stop or Yield sign should be used.

There are two types of speed limits: linear (along a portion of a highway) or area (all highways within a specified area, except those specifically excluded). Investigations to determine appropriate speed limits should include: the existing speed pattern, intersections and roadside development, traffic volumes, accident experience, and physical conditions of the highway.

For linear speed limits longer than 1100 feet, multiple speed limit signs are required. The first sign shall be placed at the beginning of the limit. The second sign should be placed within 1100 feet of the first with additional signs being placed at distances equal to 100 times the numerical value of the speed limit.