Freeway Signing Handbook: Freeway Signing Basics

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Section 2: Freeway Signing Basics

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Freeway Characteristics

Two types of guide signing are described in the Texas MUTCD. Guide signing for conventional highways (Chapter 2D) is used on highways without access control. Freeway and expressway signing (Chapter 2E) is used on highways with access control. Freeways are divided highways with full control of access. Expressways are divided highways with partial control of access. In Texas, freeways are much more common than expressways. The signing guidelines in this handbook have been developed specifically for freeways.

There are several characteristics of freeways that distinguish them from conventional roadways. These characteristics are explained in the following table.

Anchor: #i1004602Freeway Characteristics
Characteristics	Notes
Full control of access	Freeway users can enter and leave the freeway only through an entrance ramp and exit ramp.
High speeds	In free-flow conditions, freeway speeds are typically in the 50 to 70 mph range.
No intersecting traffic	Freeway users do not encounter Stop signs or traffic signals while on the freeway main lanes.
Multiple lanes	Freeways have at least two lanes in each direction of travel.

The most significant of these characteristics is the first, full control of access, which allows the existence of the other characteristics. Because of these characteristics, freeway signing typically provides a higher level of performance than signs on other types of roadways. The higher performance is typically achieved through the use of larger signs on freeways, but also includes the use of freeway guide sign practices that are different from the guide signing practices on conventional roadways.

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Philosophy of Freeway Guide Signs

Freeway guide signs and conventional guide signs are based on different philosophies, as explained below:

Freeway Guide Signs. The major emphasis of freeway signing is on destinations. Control cities and street names provide the primary exiting information for drivers. Route signs and cardinal directions are used in freeway signing, but they are not emphasized to the same extent as control cities and street names. Guidance information, such as the destination (control city, street, or highway), is provided in advance of the exit. Information is shown in Advance Guide signs and repeated in Exit Direction signs.

Conventional Guide Signs. The major emphasis of conventional guide signing is on highway class, number, and cardinal direction. This information is provided at the intersection where the maneuver is performed. Destination information (cities) is provided in advance of the intersection and is not repeated at the intersection.

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Information Provided by Freeway Signing

Due to the high-speed and high-volume nature of freeways, freeway signing should strive to provide information in a manner that contributes to quick processing and conveys clear meaning. Key factors to consider include:

Freeway signing should provide information to meet the needs of the unfamiliar road users.
Freeway signing provides advance information about approaching decision points in a manner that allows adequate time for response at freeway speeds.
Freeway signing does not have to identify every possible choice for the driver.
Freeway signing may direct the road user along a longer distance route to simplify the guidance information associated with reaching the indicated destination.

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Information Processing

The concept of positive guidance is often used as a guiding principle for providing information to drivers. Positive guidance consists of creating and maintaining a driving environment that has the following characteristics:

Motorists are provided with the maximum amount of useful visual information.
Information is presented in such a way that it is prioritized in importance.
Information is presented uniformly, allowing drivers to develop expectations about the location of information.
Information is visible under most, if not all, environmental conditions.

If the principles of positive guidance are applied consistently, drivers will subconsciously develop expectations about where to seek information. In applying the concepts of positive guidance, it is important to understand the demands that are placed on the driver during the driving task. The driving task is made up of a number of subtasks that require varying levels of time and cognitive activity. The three most basic subtasks are control, guidance, and navigation. These subtasks are explained in the following table.

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Subtask	Explanation
Control	Consists primarily of steering control and speed control.
Guidance	Consists of maintaining a safe and efficient path relative to all factors in the roadway environment. Some examples of actions included in the guidance subtask are car following, passing, and response to traffic control devices.
Navigation	Portion of the driving task most directly affected by freeway guide signing. Consists of planning a trip from beginning to end and then executing the trip plan. The navigation subtask can be broken down into trip preparation and planning, and direction finding. Trip preparation and planning can consist of anything from drivers using their own mental map of an area to consulting maps or knowledgeable persons in order to plan a trip. Direction finding occurs while drivers are en route and attempting to reach their destinations. This portion of the subtask involves interpreting direction guidance on signs to obtain information about the appropriate path.

Performance of these subtasks allows drivers to maintain their positions in the lane and find their way to their destinations. Drivers perform these subtasks continuously at various cognitive levels, although the amount of attention and cognitive resources allocated to each task may vary depending on the specific conditions present at a given point and time. The following table describes the characteristics of each of these subtasks.

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Characteristics	Control Subtask		Guidance Subtask	Navigation Subtask
	Steering Control	Speed Control		Trip Preparation and Planning	Direction Finding
Priority	High	High	Varies depending on conditions, but usually intermediate between control and navigation	Performed pre-trip, so no demands on driver while en route	Usually lowest of all subtasks, although demands may increase in complex or unfamiliar situations
Driver Level of Effort	Varies depending on geometrics	Varies depending on geometrics and traffic	Higher than control subtask, with more conscious decision-making necessary	Varies depending on driver familiarity with route	Guide signs, Route signs, Street Name signs, landmarks, etc.
Information	Vehicle response characteristics, relative position of vehicle	Vehicle braking and acceleration characteristics, road conditions ahead of driver	Traffic conditions, road geometry, weather conditions, and other information that impacts the road environment	Location or origin and destination, and physical or mental map of alternative routes	Guide signs, Route signs, Street Name signs, landmarks, etc.
Demand on Drivers	Usually low because subtask is overlearned	Greater than steering since driver must look farther down the road	Varies depending on the driver’s previous experiences and prior knowledge	Usually low	Usually low, except in unusual circumstances

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Attention and Expectation

Attention is an important component of the driving task. When a subtask has a low demand, it can be performed with little conscious attention, allowing the driver to allocate attention to tasks that require more cognitive resources. When the demands of the driving task require more attention be placed on a particular subtask, it comes at the expense of performing tasks requiring a higher level of attention. This process is known as load shedding. For example, a driver on an uncongested freeway can easily perform navigational subtasks. If traffic becomes extremely congested, the navigational subtasks become more difficult to perform because the driver must allocate more attention to the control and guidance subtasks.

Expectation is also very important in the driving task. Drivers need to have a reasonable expectation about how their vehicles will perform, the geometry of the road downstream of their positions, and where to find navigational information. If the expectation of the driver is violated, the performance of the driving task may suffer. This situation is particularly important in freeway guide signing where the unfamiliar driver will rely on guide signs to provide information to perform the navigation subtask.

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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.

Anchor: #i1005702Desirable 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.

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Figure 2-1. Example of sign information units.

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Driver Information Overload

National Cooperative Highway Research Program (NCHRP) Project 3-50 produced a report (see below) and a computer program that provides a means of analyzing driver information overload (DIO). Drawing on the results of the project and previous research, the NCHRP determined that, as a general rule, an individual guide sign is likely to cause DIO for some drivers if it contains more than two destinations or route symbols, especially if the word length exceeds seven letters.

Where multiple signs are on a sign structure, DIO can result from any of the following:

two sign panels with more than two destination names and two route symbols on any one sign
three guide sign panels with any one sign having more than two destination names
more than three sign panels, regardless of message content.

DIO is likely to occur at locations where information is dense in terms of proximity of signs and sign message content. More specifically, DIO is likely where spacing between two guide signs, including supplemental signs, is less than 800 ft, where there is one destination on the second sign, and 1200 ft where there are two or three destinations on the second sign.

Report and Program Available. The computer program (CRP-CD-36) developed through NCHRP Project 3-50 is included with the report when the report is ordered from the Transportation Research Board. (Lerner, N.D., R.E. LLaneras, H.W. McGee, Sunil Taori, and G. Alexander. Additional Investigations on Driver Information Overload, NCHRP Report 488, Transportation Research Board, Washington, D.C., 20003)