Boone County Public Works Department

Traffic Safety Manual - Boone County, Missouri

2.0 TRAFFIC SIGNING AT INTERSECTIONS

Traffic control devices are necessary for regulating, warning, and guiding traffic, and are a primary determinant in the safe and efficient operation of intersections.   The Manual on Uniform Traffic Control (MUTCD) outlines national standards for when and where traffic control is warranted.   American Association of State Highway and Transportation Officials (AASHTO) sets forth guidelines for variables that impact traffic control such as sight distance requirements.

 

The uses of regulatory signs inform highway users of traffic laws or regulations and indicate the applicability of legal requirements that would not otherwise be apparent.   Common regulatory signs include the STOP sign (R1-1) and YIELD sign (R1-2).   The use of the Street Name sign informs the highway user of the street location and enables the highway user and the safety personnel to navigation to homes, businesses, etc.   The application of stop signs, multiway stop signs, yield signs, and street name signs are discussed in the following sections.

2.1 Stop Signs

STOP signs are intended for use where traffic is required to stop.   The standard size of a STOP sign used in Boone County will be 30-inch x 30-inch and the bottom of the sign will not be less than 5 feet from the ground.   Where greater emphasis or visibility is required, a larger size sign should be considered.  

 

Table 1 summarizes the condition that may require the use of the STOP sign.   The STOP sign should be used only where warranted because it can cause a substantial inconvenience to motorists.   Prior to the application of a STOP sign, consideration of less restrictive measures, such as the YIELD sign should be examined.   Periodic reviews of existing installations may be conducted to determine if less restrictive control or no control could accommodate traffic demands safely and more effectively.

 

In a situation where two main highways intersect, the STOP sign or signs should normally be posted on the minor street to stop the lesser flow of traffic.   Traffic engineering studies, however, may justify the installation of a STOP sign or signs on the major street.   Such a situation may occur at a three-way intersection where safety considerations may justify stopping the greater flow of traffic to permit a left-turning movement.  

 

STOP Signs will be replaced by the County within 24 hours of notification that a STOP Sign has been stolen or damaged.

2.2 Multiway Stop Signs

A multiway stop installation is useful as a safety measure at some locations.   Table 1 includes conditions that may warrant the installation of a multiway stop.

 

At a multiway stop intersection, Boone County will use a supplementary plate (R1-3) 12-inch x 6-inch in size that will be mounted just below the STOP sign.   If the number of approach legs to the intersection is three or more, the numeral on the supplementary plate shall correspond to the actual number of legs (i.e., 3-WAY or 4-WAY).   If all streets of the intersection are controlled by STOP signs, the supplementary plate may state ALL-WAY, instead of the number of approach legs.

Table 1 .   Summary of Guidance and Options for Stop and Multiway Stop Conditions

Traffic Control Devices

Conditions That Might Warrant a STOP Sign

STOP Sign

(R1-1)

1. Intersection of a less important road with a main road where application of the normal right-of-way rule would not be expected to provide reasonably safe operation.

Standard Size

Table130”x30”

2. Street entering a through highway or street.

 

3. Unsignalized intersection in a signalized area.

 

4. High speeds, restricted view, or crash records indicate a need for control by the STOP sign.

MULTIWAY STOP Signs (R1-1)

1. Where traffic signals are justified, the multiway stop is an interim measure that can be installed quickly to control traffic while arrangements are being made for the installation of the traffic control signal.

use in conjunction with (R1-3)

Table1

2. A crash problem, as indicated by 5 or more reported crashes in a 12-month period that are susceptible to correction by a multiway stop installation.   Such crashes include right- and left-turn collisions as well as right-angle collisions.

 

3. Minimum volumes:

 

a) The vehicular volume entering the intersection from the major street approaches (total both approaches) must average at least 300 vehicles per hour for any 8 hours of an average day, and

Table1

 

 

R1-3 (12”x6”)

Table1

b) The combined vehicular, pedestrian, and bicycle volume entering the intersection from the minor street approaches (total of both approaches) average at least 200 units per hour for the same 8 hours, with an average delay to minor street vehicular traffic of at least 30 seconds per vehicle during the highest hour, but

R1-4 (18”x6”)

c) If the 85th-percentile approach speed of the major street traffic exceeds 40 miles per hour, the minimum vehicular volume warrants are 70 percent of the above requirements.  

 

4. Where no single criterion is satisfied, but where criteria 2, 3a, and 3b are all satisfied to 80 percent of the minimum values.   Criterion 3c is excluded from this condition.

 

5. Other criteria that may be considered in an engineering study include:

 

a) The need to control left-turn conflicts;

 

b) The need to control vehicle/pedestrian conflicts near locations that generate high pedestrian volume;

 

c) Locations where a road user, after stopping cannot see conflicting traffic and is not able to safely negotiate the intersection unless conflicting cross traffic is also required to stop; and

 

d) An intersection of two residential neighborhood collector (through) streets of similar design and operation characteristics where multiway stop control would improve traffic operational characteristics of the intersection.

For ADT<=400

1. For low-volume roads where engineering judgment or study indicates that either of the following conditions applies:

 

a) An intersection of a less-important road with a main road where application of the normal right-of-way rule might not be readily apparent; or

 

b) An intersection that has restricted sight distance for the prevailing vehicle speeds.

Source:   Manual on Uniform Traffic Control Devices, Millennium Edition. (Section 2B.05 through 2B-07, &   5B.03)

2.3 Yield Signs

The YIELD sign assigns right-of-way to traffic on certain approaches to an intersection.   Vehicles controlled by a YIELD sign need stop only when necessary to avoid interference with other traffic that is given the right-of-way.   Table 2 outlines conditions when a YIELD sign may be warranted.

 

The standard size of a YIELD sign used in Boone County will be 36-inch x 36-inch x 36-inch and the bottom of the sign not be less than 5 feet from the ground.   YIELD signs generally should not be placed to control the major flow of traffic at an intersection.   However, YIELD signs may be installed to control traffic movement where a majority of drivers in that movement are making right turns.   At such an intersection, YIELD signs should not be erected on more than one approach.   Table 2 summarized the guidance and options conditions for YIELD sign usage as outlined in the MUTCD.

Table 2.   Summary of Guidance and Options for Yield Conditions

Traffic Control Devices

Conditions That Might Warrant a YIELD Sign

YIELD Sign                 (R1-2)

1. At the entrance to an intersection where it is necessary to assign right-of-way and where the safe approach speed on the entrance exceeds 10 miles per hour.

Standard Size             36" x 36"x 36"

2. If controlling a merge-type movement on the entering roadway where acceleration geometry and/or sight distance is not adequate for merging traffic operations.

Yield Sign - Table 2 

3. At the second crossroad of a divided highway, where the median width is 30 feet wide or greater.   A STOP sign may be installed at the entrance to the first roadway of the divided highway, and a YIELD sign may be placed at the entrance to the second roadway.

 

4. At an intersection where a special problem exists and where engineering judgment indicates the problem to be susceptible to correction by use of the YIELD sign.

For ADT<=400

1. For low-volume roads where engineering judgment or study indicates that either of the following conditions applies:

 

a) An intersection of a less-important road with a main road where application of the normal right-of-way rule might not be readily apparent; or

 

b) An intersection that has restricted sight distance for the prevailing vehicle speeds.

Source:   Manual on Uniform Traffic Control Devices, Millennium Edition. (Section 2B.08 through 2B-09,&   5B.03)

2.4 Location of Stop Sign and Yield Sign

A STOP sign should be erected at the point where the vehicle is to stop or as near thereto as possible.   If accident trends or engineering analysis indicate a reoccurring violation of this standard, the County should consider adding a stop line and/or the word STOP on the pavement.   A YIELD sign should be erected in the same manner, at the point where the vehicle is to stop if necessary to yield the right-of-way.   Where a marked crosswalk on pavement exists, the sign should be erected approximately 4 feet in advance of the crosswalk line nearest to approaching traffic.   Stop signs and yield signs will be located on county maintained roads and/or private roads where they intersect county maintained roads when warranted.

 

In a situation where the visibility of a STOP sign or a YIELD sign is restricted, the STOP sign or YIELD sign shall be located as specified, and a STOP AHEAD (W3-1a) or a YIELD AHEAD (W3-2a) sign shall be erected in advance of the STOP or YIELD sign.   The minimum standard size for the STOP AHEAD and YIELD AHEAD warning signs to be used will be 30-inch x 30-inch.   In instances where there is a history of poor observance of the STOP sign, the County will install a STOP AHEAD warning sign.   The placement of the STOP AHEAD and YIELD AHEAD sign shall be determined from Table 6 on page 11.   Figure 1 displays the advance warning signs to be used by Boone County .

Figure 1 .   Stop Ahead and Yield Ahead Warning Signs

Stop Ahead Signs

2.5   Intersections with No Traffic Control

In a situation where an intersection crossing is not controlled by yield signs, stops signs, or traffic signals, the operator of a vehicle approaching an intersection must be able to perceive a hazard in sufficient time to alter the vehicle’s speed as necessary before reaching the intersection.   Figure 2 displays an intersection with no traffic control.   In this situation, no obstructions should be present within the sight triangle.   To determine the appropriate distance (d) of the sight triangle legs, the speeds along the major and minor roads should be determined.   Based upon these speeds, Table 3 will be used to determine the dimensions of the sight triangle legs.

Figure 2 .   Example of Intersection with No Traffic Control

No Traffic Control Image

Table 3.   Sight Distance required at No Control Intersections

Speed

(mph)

ADT > 400

ADT <= 400

Distance "d" of the Sight Triangle Leg 1,3

(feet)

Distance "d" of the Sight Triangle Leg 2,3

(feet)

15

70

60

20

90

80

25

115

95

30

130

120

35

145

140

40

180

170

45

200

210

50

220

255

55

250

300

60

280

350

Notes:       1. Source:   A Policy on Geometric Design of Highways and Streets, AASHTO, 1994. (Table IX-7, page 699)

2. Source:   Guidelines for Geometric Design of Very Low-Volume Roads, 2001 (Exhibit 14, p.45)

3. Additional consideration should be given to intersection approaches that exceed 3 percent grade.

For example, a roadway at 40 miles per hour intersecting a roadway at 25 miles per hour and an average daily traffic (ADT) of greater than 400 vehicles per day would result in the legs of the sight triangle equal to 180 feet and 115 feet respectively.   These, or greater distances, will permit a vehicle on either road to change speed before reaching the intersection.

 

Non-controlled intersections should be used only in the design of intersections on two lane roads where sight distances are adequate.   Intersections with sight triangles having adequate sight distance may still require control based on engineering judgment.   Where this minimum sight triangle cannot be provided, traffic control devices should be used to slow down or stop vehicles on one or both roads even if both roads are lightly traveled.   Existing conditions will be addressed as they become evident and as funding allows.

2.6 Intersection Stopping Sight Distance

Sight distance is the length of roadway ahead visible to the driver.   The minimum stopping sight distance available on a roadway is the distance to enable a vehicle traveling at or near the design speed to stop before reaching a stationary object in its path.   Table 4 outlines the stopping sight distance guidelines.

Table 4.   Stopping Sight Distance Requirements

Design Speed

(mph)

ADT > 400

ADT <= 400

Minimum Stopping Sight Distance 1

(feet)

Minimum Stopping Sight Distance 2

(feet)

20

100

95

25

150

125

30

190

165

40

250

250

45

310

300

50

370

350

55

430

405

60

515

470

Source:        1. A Policy on Geometric Design of Highways and Streets, AASHTO, 1994. (page 120)

2. Guidelines for Geometric Design of Very Low Volume Local Roads, 2001 (Exhibit 8, p.34)

Where adequate stopping sight distance at the intersection is not available to the through traffic at the posted speed, then intersection warning signs (W2-1 through W2-5) should be installed on the uncontrolled road approaches.   The standard size of the intersection warning signs used in Boone County will be 30-inch x 30-inch.   Examples of these signs are displayed in Figure 3.   The placement of these signs is determined by using Table 6 on page 11.

Figure 3 .   Intersection Warning Signs

Intersection Warning Signs

Source:   Manual on Uniform Traffic Control Devices, Millennium Edition. (section 2C.34).

2.7  Unwarranted Traffic Control Devices

Stop signs will not be installed by the County solely to control vehicle speeds or divert traffic. STOP signs installed in the wrong places for the wrong purposes can create more problems than are solve.   Studies have shown that there is a high incidence of intentional violations where stop signs are installed to control speed.   These studies showed that vehicle speed was reduced in the immediate vicinity of the stop signs, but vehicle speeds were actually higher between intersections than they would have been if these signs had not been installed.   At the right place and under the right conditions, a STOP sign tells the drivers and pedestrians who has the right of way.

 

2.8  Street Name Signs

Street Name signs are used to identify roads and are installed at street intersections regardless of other route signs.   For roads with a speed limit less than 60 miles per hour, the Street Name sign lettering height shall be at least 6 inches for upper case-letters and 4.5 inches for lower-case letters.   For local roads with a speed limit of 60 miles per hour or greater, the Street Name sign lettering height shall be at least 9 inches for upper case-letters and 6 inches for lower-case letters..   At intersections with two different speed limits, the higher speed limit will prevail when determining Street Name sign letter height.

 

Any supplementary lettering to indicate the type of street, such as Street, Avenue, or Road, shall have a minimum height of 3 inches and conventional abbreviations may be used.   Coordinates shall be used for all County maintained roads, except for internal subdivision roads or roads of shared jurisdiction with municipalities.   The coordinates shall be located on the top, right hand corner of the Street Name sign and shall be a minimum of 2 inches in height.  

 

The Street Name sign shall be retroreflective or illuminated to show the same shape and similar color both day and night.   Street Name signs for all county maintained roads shall have a white legend on a green background.   Street Name signs for all privately maintained roads shall have a black legend on a white background.   An informational placard stating it is a private road will be placed below the Street Name sign.

 

At intersections of crossroads where the same road has two different street names for each direction of travel, both street names may be shown on the same signpost.   Directional arrows shall be used to designate the street name to the location of the street.  

 

Divided highways that intersect with County maintained roads may have Street Name signs placed on each side of the intersections unless placement of a sign in the median is permitted.   On principal arterials, Street Name signs should be placed at least on diagonally opposite corners so that they will be on the far right side of the intersection for traffic on the major street.   In subdivisions and rural intersections, at least one Street Name sign should be located at each intersection.   The Street Name sign for each road of the intersection shall be mounted on the same post and the Street Name sign faces shall be parallel to the street they name.   The Street Name signs shall be at installed least 5 feet off the ground measured from the bottom of the sign to the near edge of the pavement.   Street Name signs may be mounted on the same post as Stop or Yield signs.

 

The County shall post and maintain Street Name signs on all county maintained roads and at the entrances of privately maintained roads.   The Street Name signs shall only contain street names adopted by the Commission.   The Street Name sign posting of the privately maintained roads will be located at the intersection of the county maintained road and the privately maintained road within the county right-of-way, whenever possible.   If the privately maintained road intersects with a State right of way, the Street Name sign will be placed in the State right of way as permitted.   The County will not provide and maintain Street Name signs for the internal roads of a privately maintained subdivision.

 

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Last Updated: December 27, 2010