Minnesota Department of Transportation

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Signing specifications

Why are some cities included on the large green guide signs at interstate highway intersections?

There is a national publication by the American Association of State Highway and Transportation Officials (AASHTO) that lists what are referred to as control cities. Control cities are “cities which have been determined by each state to be major destinations and population centers located on or near the Interstate Highway System.” These cities are listed sequentially on guide signs along the interstate, and remain on successive signs until that destination is reached.

What is the purpose of the numbers on signs every mile along state highways?

These are called reference location signs. They are installed every mile on all state highways. The beginning reference point is "0" at the western border of the state for east/west highways and "0" at the southern border of the state for north/south highways. If the highway does not extend to a western or southern border, then the beginning reference point is at the westernmost or southernmost limit of the highway.

How are exit numbers determined?

Exit numbering in Minnesota is used on Interstate freeways. Exit numbering is based on the reference location signs as mentioned in the previous question (for example, an exit located between reference location sign 48 and 49 would be numbered exit number 48). If multiple exits are located within the same mile, the exit is numbered with a letter following, such as 48A and 48B. The lettering follows alphabetically from west to east and south to north.

What manuals, standards, sample plans, specifications are available for review and guidance for roadway signing?

The most frequently used signing manuals are typically:

What is the legal height for vehicles on highways and when does MnDOT install clearance signs?

The legal height for vehicles is 13 feet, 6 inches. The low clearance sign is used to warn road users of clearances less than 12 inches above this legal height. Clearance below bridges on freeways is typically 16 feet, 4 inches and for overhead mounted signs is 17 feet, 4 inches.

What is the proper mounting height for Disabled Parking signs?

If installed for a parallel parking spot on an urban street, the bottom of the sign needs to be 7 feet above the sidewalk. If installed in a parking lot, the sign must be visible to the driver when the vehicle is parked in the disabled parking space.

What does the 6% mean on a hill sign?

6% refers to the amount of slope of the highway from the top to the bottom of the hill - 6 percent means that for every 100 feet horizontally, the highway drops 6 feet. These signs are placed in advance of steep grades requiring special precaution on the part of road users.

Does MnDOT use plywood or plastic for its signs?

No. MnDOT only uses aluminum as the base material for sign panels. Sheet aluminum is used for smaller signs; larger signs and overhead mounted signs are made with extruded aluminum panels.

What type of sheeting materials does MnDOT use for its signs?

MnDOT uses sheeting materials listed on our Approved Products List. Currently, the type of material used by MnDOT is Type XI retroreflective sheeting. For other specifics on MnDOT sign sheeting materials or the Approved Products List, contact Ethan Peterson at 651-234-7380.