Limitations on Quantity of Information

Various documents have suggested limits on the amount of information that should be presented to drivers with freeway signs. The Texas MUTCD contains the following guidelines for limiting the amount of legend on freeway guide signs (Sections 2E.09 and 2E.10):
  • No more than two destination names or street names should be shown on any Advance Guide sign or Exit Direction sign.
  • A city name and street name on the same sign should be avoided.
  • Where two or three signs are placed on the same supports, destinations or names should be limited to one per sign, or to a total of three in the display.
  • Sign legends should not exceed three lines of copy.
  • Regulatory signs, such as Speed Limit signs, should not be used in conjunction with overhead guide sign installations.
  • No more than three guide signs should be displayed at any one location, either on the overhead structure or its support.
  • At overhead locations, more than one sign may be installed to advise road users of a multiple exit condition at an interchange.
  • If the roadway ramp or crossing roadway has complex or unusual geometrics, additional signs with confirming messages may be provided to properly guide the road user.
Various researchers have evaluated the amount of information to present to road users in freeway guide signs. Research by the Texas Transportation Institute recommended the guidelines shown in the following table. The table shows that placing five sign panels on a single structure is not a desirable design and should be avoided if possible. As indicated on the previous page, the Texas MUTCD recommends that no more than three guide signs be used at a single location. The maximum amount of information on any sign structure should not exceed 20 units.
Desirable and Maximum Units of Information per Freeway Guide Sign Structure*
 
Units of Information per Structure
Number of Sign Panels
Desirable
Maximum
2
12
16
3
16
18
4
18
20
5
Undesirable Design
20
* Source: McNees, R.W. and C.J. Messer. Reading Time and Accuracy of Response to Simulated Urban Freeway Guide Signs. in
Transportation Research Record 844
, Transportation Research Board, Washington, D.C, 1982.
For the above table, each of the following items is defined as one unit of information:
  • place name (examples:
    College Station
    ,
    Rockport
    )
  • street name (examples:
    Main Street
    ,
    First Avenue
    )
  • route number (examples:
    I 10
    ,
    US 59
    )
  • cardinal direction (examples:
    North
    ,
    South
    )
  • exit number (examples:
    245
    ,
    81
    )
  • command (examples:
    Exit
    ,
    Next Right
    )
  • distance (examples:
    ½ mile
    ,
    2 miles
    )
  • lane use arrows (examples:
  • junction (example:
    Jct.
    )
  • exit only (example:
    Exit Only
    )
Figure 2‑1 provides an example of how the units of information in several sign panels located on a structure would be counted.
Example of sign information units. (click in image to see full-size image)
Figure 2-1. Example of sign information units.