Maine Local Roads Center

MUTCD Standards on Speed Limits

(from Millenium Edition, 2001)
http://mutcd.fhwa.dot.gov/

Standard (mandatory):

After an engineering study has been made in accordance with established traffic engineering practices, the Speed Limit (R2-1) sign shall display the limit established by law, ordinance, regulation, or as adopted by the authorized agency. The speed limits shown shall be in multiples of 10 km/h (5 mph).

If a metric speed limit is displayed, the METRIC supplemental plaque shall be placed above the sign and the km/h supplemental plaque shall be placed below.

Support:

The METRIC supplemental plaque, which has a yellow background with a black legend and border, indicates to road users that the metric system is being used.

Guidance (recommended):

No more than three speed limits should be displayed on any one Speed Limit sign or assembly.

When a speed limit is to be posted, it should be the 85th-percentile speed of free­flowing traffic, rounded up to the nearest 10 km/h (5 mph) increment.

Option (permissible):

Other factors that may be considered when establishing speed limits are the following:

A. Road characteristics, shoulder condition, grade, alignment, and sight distance;

B. The pace speed;

C. Roadside development and environment;

D. Parking practices and pedestrian activity; and

E. Reported crash experience for at least a 12-month period.

Two types of Speed Limit signs may be used: one to designate passenger car speeds, including any nighttime information or minimum speed limit that might apply; and the other to show any special speed limits for trucks and other vehicles.

A changeable message sign that changes for traffic and ambient conditions may be installed provided that the appropriate speed limit is shown at the proper times. 

Support: 

Advisory Speed signs are discussed in Sections 2C.33 and 2C.42 and Temporary Traffic Control Zone Speed signs are discussed in Part 6.

Section 2B.15 Location of Speed Limit Signs

Standard (mandatory):

Speed Limit (R2-1) signs, indicating speed limits for which posting is required by law, shall be located at the points of change from one speed limit to another.

At the end of the section to which a speed limit applies, a Speed Limit sign showing the next speed limit shall be installed. Additional Speed Limit signs shall be installed beyond major intersections and at other locations where it is necessary to remind road users of the speed limit that is applicable.

Speed Limit signs indicating the statutory speed limits shall be installed at entrances to the State and at jurisdictional boundaries of metropolitan areas.

Section 2B.16 Reduced Speed Ahead Signs (R2-5 Series)

Guidance (recommended):

The Reduced Speed Ahead (R2-5 series) signs should be used to inform road users of a reduced speed zone when engineering judgment indicates the need for advance notice to comply with the speed limit posted ahead.

This sign should not be used in urban areas where speeds are relatively low.

Standard (mandatory):

The Reduced Speed Ahead (R2-5 series) signs shall be followed by a Speed Limit (R2-1) sign installed at the beginning of the zone where thespeed limit applies

Option (permissible):

The following methods may be used to provide road users with advance notice of a change in the speed limit:

A. Any of the R2-5 series of signs may be displayed.

B. An assembly consisting of the Speed Limit (R2-1) sign with a supplemental legend plaque BEGIN mounted above the R2-1 sign and a supplemental distance plaque, such as 1/6 km or 1/4 mi, mounted below the R2-1 sign may be displayed.

Guidance (recommended):

When used with Speed Limit assemblies, the supplemental plaques should have a white background with a black legend and border, except for the METRIC plaque (see Section 2B.11).