Chapter 29.28
ARTERIAL AND COLLECTOR GEOMETRIC DESIGN, INCLUDING ROUNDABOUTS

Sections:

29.28.010    Geometric standards.

29.28.020    Arterial and collector streets.

29.28.030    Right-of-way, street lane widths, and street lengths.

29.28.040    Alignments – Horizontal alignment.

29.28.050    Alignments – Vertical alignment – Grades.

29.28.060    Clearance of structures.

29.28.070    Stopping sight distance.

29.28.080    Cross section.

29.28.090    Tapers and transitions – Road width transition tapers.

29.28.100    Bicycle treatments.

29.28.110    Intersections.

29.28.120    Unsignalized intersections.

29.28.130    Signalized intersections.

29.28.140    Sight distance.

29.28.150    Sight zones.

29.28.160    Intersection radii.

29.28.170    Lane requirements.

29.28.180    Angles.

29.28.190    Grades.

29.28.200    Spacing and offsets.

29.28.210    Pedestrian treatments.

29.28.220    Roundabouts.

29.28.230    Landscaping – General requirements.

29.28.010 Geometric standards.

Geometric standards have been developed to provide adequate safety for the traveling public. This chapter sets the minimum standards for geometric design of streets classified as collector and above, as shown on the Grand Junction Circulation Plan. These streets are intended for higher volumes and faster traffic than the residential streets discussed in Chapter 29.20 GJMC. They function in transition from direct land use access to movement of traffic.

Roundabouts provide safety improvements, less delay than other forms of control, community enhancement and increased traffic circulation at some intersections. Roundabouts can efficiently handle many intersections with decreased delay and greater efficiency than traffic signals. This chapter defines the modern roundabout and provides a link to general design criteria.

(Res. 39-04 (§ 6.0), 4-21-04)

29.28.020 Arterial and collector streets.

(a)    General Requirements. Major arterials shall be designed to provide a high degree of mobility and serve longer trips, implying a higher operating speed and level of service. These streets are designated on the Grand Junction Circulation Plan. Minor arterial streets interconnect with and augment the major arterial system. These streets accommodate trips of shorter lengths and may also serve more access functions than the major arterial streets.

(b)    Collector streets provide both land access and movement within residential, commercial and industrial areas. Operating speeds are lower than arterial streets.

(c)    Pedestrians and bicyclists are users of the street system and street design needs to include consideration for them. The adopted Grand Junction Circulation Plan shows existing and future pedestrian and bicycle facilities.

(Res. 39-04 (§ 6.1), 4-21-04)

29.28.030 Right-of-way, street lane widths, and street lengths.

The required right-of-way width for a street is indicated in the City Standard Street Details. Additional widths may be required for needed through and turn lanes, and where it is necessary to accommodate slopes and drainage structures.

(a)    Principal Arterial (No On-Street Parking).

(b)    Minor Arterial (No On-Street Parking).

(c)    Collector (No On-Street Parking).

(d)    D 1/2 Road Section (No On-Street Parking).

(e)    D Road Section (No On-Street Parking).

(f)    G Road Sections.

(Res. 39-04 (§ 6.1.1), 4-21-04)

29.28.040 Alignments – Horizontal alignment.

Streets shall extend to the boundary lines of the land to be subdivided. Proposed streets with widths different from existing streets to which they are being connected must be transitioned using pavement transition taper standards.

All designs shall be based on the horizontal curve design criteria.

Horizontal Curve Design Criteria

Design Criteria

Major1

Collector

Arterial

Min. Design Speed (mph)

35

40

Min. Center2 Line Radius (ft)

470

SEE4

Min. Horizontal Sight Distance (ft)

250

325

Min. Reverse Curve Tangent (ft)

200

200

Min. Approach3 Tangent at Intersections

200

300

1    These criteria are to be used without superelevation.

2    Radii shown are based on the street having a crown section with a pavement cross-slope of two percent on each side of the crown. For minimum radii required for other cross-slopes or where superelevation is provided and approved, see Exhibit 3-40 in “A Policy on Geometric Design of Highways and Streets,” AASHTO, 2001 Edition.

3    Where a curved road approaches an intersection, these tangent sections must be provided on the approach to the intersection to provide for adequate sight distance for traffic control devices at the intersection.

4    The maximum superelevation rate allowed is e = six percent. Where superelevation is used, runoff lengths shall conform to Exhibit 3-41 in “A Policy on Geometric Design of Highways and Streets,” AASHTO, 2001 Edition.

(Res. 39-04 (§ 6.1.2), 4-21-04)

29.28.050 Alignments – Vertical alignment – Grades.

Grades, curve length and vertical sight distance shall be designed to ensure proper drainage, sight distance and safety for vehicles and pedestrians. Grades of streets shall not be less than 0.5 percent. The grade of a street may be reduced only when matching existing streets or property. Maximum street grades shall be eight percent. For algebraic differences of 0.5 percent or less, grade breaks shall be required for adequate drainage.

Design Controls for Vertical Curves

Design Speed MPH

Stopping Sight Distance (feet)

Crest “K” Values

Sag “K” Values

20

115

7

17

25

155

12

26

30

200

19

37

35

250

29

49

40

305

44

64

45

360

61

79

50

425

84

96

55

495

114

115

60

570

151

136

From Exhibits 3-76 and 3-79, AASHTO, “A Policy on Geometric Design of Highways and Streets,” 2001.

1    All minimum stopping sight distances for vertical curves with crests must be shown on the construction plans. Sight distances are based on design speeds.

(Res. 39-04 (§ 6.1.3.1), 4-21-04)

29.28.060 Clearance of structures.

A minimum of 17.5 feet shall be provided for all overhead sign structures. The clearance shall be measured from the crown of the street to the lowest portion of the structure. A minimum vertical clearance of 16 feet for all other structures shall be provided on all arterial streets and designated truck routes. A minimum clearance of 14 feet may be allowed on collector streets.

(Res. 39-04 (§ 6.1.3.2), 4-21-04)

29.28.070 Stopping sight distance.

“Stopping sight distance” is defined as the length of roadway ahead visible to the driver. The minimum stopping sight distance available on a roadway must be sufficiently long to enable a vehicle traveling at or near the roadway design speed to stop before reaching a stationary object in its path or react to a traffic control device such as a stop sign.

The appropriate stopping sight distance shall be provided. The distances shown assume vehicles traveling on wet pavement on flat grades. Factors that take into account the effect of grade on stopping sight distance shall be used in determining appropriate stopping sight distance where the grades are three percent or higher.

Minimum Stopping Sight Distance

Design Speed (MPH)

Stopping Sight Distance (Ft.)

20

115

25

155

30

200

35

250

40

305

45

360

50

425

55

495

60

570

Based on Exhibit 3-1, AASHTO, “A Policy on Geometric Design of Streets and Highways,” 2001.

Effect of Grade on Stopping Sight Distance

Design Speed (MPH)

Downgrades

Upgrades

3%

6%

9%

3%

6%

9%

20

116

120

126

109

107

104

25

158

165

173

147

143

140

30

205

215

227

200

184

179

35

257

271

287

237

229

222

40

315

333

354

289

278

269

45

378

400

427

344

331

320

50

446

474

507

405

388

375

55

520

553

593

469

450

433

60

598

638

686

538

515

495

From Exhibit 3-2, AASHTO, “A Policy on Geometric Design for Highways and Streets,” 2001.

(Res. 39-04 (§ 6.1.3.3), 4-21-04)

29.28.080 Cross section.

(a)    Cross Slopes. The typical cross slope is two percent crown to provide for adequate drainage to the pavement edge. The maximum cross slope on the tangent sections shall not exceed four percent. The minimum cross slope shall be one percent.

(b)    Superelevation. Superelevation shall be designed in accordance with the horizontal curve design criteria (GJMC 29.28.040).

(c)    Clear Zones. All roadways shall meet clear zone requirements as set forth in AASHTO Roadside Design Guide, 1989 Edition. Where under-improved streets are constructed (for example, a half-street construction), the minimum shoulder width shall be provided.

(d)    Roadside Barrier and Bridge Rails. Roadside barriers shall be required in accordance with warrants, design criteria and standards for roadside barriers and bridge rails as defined in the AASHTO Roadside Design Guide, 1989 Edition or latest.

(Res. 39-04 (§ 6.1.4), 4-21-04)

29.28.090 Tapers and transitions – Road width transition tapers.

When constructing a roadway that will connect with an existing roadway of a different width, a transition taper is required. These ratios are not to be used in the design of exclusive turn lanes.

Minimum Road Width Transition Tapers

Design Speed (MPH)

Transition Run/Offset (Ft/Ft)

30 or less

15 / 1

35

20 / 1

40

25 / 1

45

45 / 1

50

50 / 1

55

55 / 1

60

60 / 1

Table based on Section 3B-8, MUTCD.

(Res. 39-04 (§ 6.1.5), 4-21-04)

29.28.100 Bicycle treatments.

Bicycle facilities are required as shown on the Grand Junction Circulation Plan. Provisions for bicycle facilities shall be in accordance with the AASHTO Guide for Development of New Bicycle Facilities 1999.

(Res. 39-04 (§ 6.1.6), 4-21-04)

29.28.110 Intersections.

Generally, there are two types of intersections: unsignalized and signalized. Each of these may have several different configurations and levels of traffic control. A roundabout is a form of an unsignalized intersection and is specifically discussed in GJMC 29.28.220. All intersections shall conform to the guidelines set forth in AASHTO and the MUTCD.

(Res. 39-04 (§ 6.2), 4-21-04)

29.28.120 Unsignalized intersections.

There are three acceptable levels of traffic control at unsignalized intersections: yield controlled, two-way stop controlled and all-way stop controlled. The appropriate use of each of these is discussed in the following subsections.

(a)    Yield Controlled Intersections. Yield controlled intersections will not generally be allowed, except at roundabouts.

(b)    Two-Way Stop Controlled Intersections. Stop signs shall be used in accordance with the MUTCD.

(c)    All-Way Stop Controlled Intersections. An all-way or “multi-way” stop installation shall be used only where the criteria of the MUTCD are met.

(Res. 39-04 (§ 6.2.1), 4-21-04)

29.28.130 Signalized intersections.

A signalized intersection shall only be installed after a careful analysis and engineering study of the roadway and traffic conditions at the intersection and on the corridor. When a signal is proposed on a corridor where signals are coordinated, the TIS shall analyze the impacts to the progression of traffic on the corridor and on surrounding land uses. This analysis shall include the progression bandwidth, efficiency and level of service determinations, signal timing and phasing including pedestrian movements, and an analysis of the storage queue lengths for exclusive turn lanes. Signal installations shall meet the spacing criteria in GJMC 29.28.200. Traffic signal warrants and design criteria are thoroughly discussed in the MUTCD, Part IV.

(Res. 39-04 (§ 6.2.2), 4-21-04)

29.28.140 Sight distance.

Street intersections and private access to public streets shall be planned and located to provide as much sight distance as possible. At a minimum, there must be sufficient sight distance for the driver on the minor street or driveway to cross or turn onto the intersecting street. Minimum sight distance values are provided for passenger cars turning left or right from a minor street. When grades are steeper than three percent, adjustment factors must be applied.

The operating speed on each approach is assumed to be, in order of desirability, (a) the eighty-fifth percentile speed, (b) the speed limit if based on an engineering study, or (c) in the case of a new facility, 80 percent of the design speed.

Minimum Sight Distance for Left and Right Turns onto Major Street by Passenger Cars at Stop-Controlled Intersections

Major Street Speed

Minimum Sight Distance

20 MPH

200′

25 MPH

275′

30 MPH

350′

35 MPH

400′

40 MPH

500′

45 MPH

550′

50 MPH

600′

55 MPH

700′

Table based on Table 11-15 of the ITE Traffic Engineering Handbook, 5th Edition.

Factors for the Effect of Grade on Sight Distance

Approach Grade (%)

Design Speed (MPH)

 

15

20

25

30

35

40

45

50

55

60

-6

1.1

1.1

1.1

1.1

1.1

1.1

1.1

1.2

1.2

1.2

-5

1.0

1.0

1.1

1.1

1.1

1.1

1.1

1.1

1.1

1.1

-4

1.0

1.0

1.0

1.1

1.1

1.1

1.1

1.1

1.1

1.1

-3 to +3

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

+4

1.0

1.0

1.0

1.0

1.0

0.9

0.9

0.9

0.9

0.9

+5

1.0

1.0

1.0

0.9

0.9

0.9

0.9

0.9

0.9

0.9

+6

1.0

1.0

0.9

0.9

0.9

0.9

0.9

0.9

0.9

0.9

Based on Exhibit 9-53, AASHTO, “A Policy on Geometric Design for Highways and Streets,” 2001.

(Res. 39-04 (§ 6.2.3), 4-21-04)

29.28.150 Sight zones.

Within the sight zone there shall be no sight-obscuring sign, wall, fence, berming, or other object higher than 30 inches, or in the case of trees, no foliage lower than eight feet. Vertical measurement shall be made from the flowline of the adjacent gutter or, if no gutter exists, from the edge of the nearest traveled way. Objects that may be located in the sight zones are items such as hydrants, utility poles, and traffic control devices. These shall be located to minimize visual obstruction.

(Res. 39-04 (§ 6.2.3.1), 4-21-04)

29.28.160 Intersection radii.

Minimum intersection radii must be maintained at public street intersections.

Minimum Intersection Flowline Radii

Through Street2

Intersecting Street

Arterial

Collector

Local Residential

Local Commercial

Local Industrial1

Arterial

35′

30′

30′

30′

30′

Collector

30′

30′

25′

30′

30′

1    Radii at intersections with industrial streets shall be individually designed based on the turning requirements for the type of truck that will most commonly use the street.

2    At signalized intersections where right-turn channelization islands are provided or high truck and bus volumes may use the access, a larger flowline radius may be required.

(Res. 39-04 (§ 6.2.4), 4-21-04)

29.28.170 Lane requirements.

Lane design through an intersection shall be consistent with the lane design of the streets forming the intersection.

(a)    Lane Widths. Lane widths shall be consistent with the cross-sections as shown in the City Standard Street Details.

(b)    Exclusive Turn Lanes.

(1)    The purpose of an exclusive turn lane is to expedite the movement of through traffic, increase intersection capacity, permit the controlled movement of turning traffic, and promote the safety of all traffic. The provision of left-turn lanes is essential from both capacity and safety standpoints where left turns would otherwise share the use of a through lane. Right-turn lanes remove the speed differences in the main travel lanes, reducing the frequency and severity of rear-end collisions.

(2)    Separate right-turn lanes shall be required in accordance with the right-turn warrant chart. Separate left-turn lanes shall be required at all new signal locations and at unsignalized locations in accordance with the left-turn warrant chart.

Warrants for Right-Turn Lanes

Two Lane Roadways

Number of Peak Hour Turning Vehicles

DDHV (vph)

35 MPH or less

40 MPH

45 MPH

50 MPH

55 MPH

200

 

 

 

73

35

300

 

 

120

41

24

400

200

200

50

30

19

500

150

125

35

25

16

600

75

50

25

20

14

800

50

30

15

15

11

1,000

25

25

15

11

9

1,200

20

20

15

9

8

DDHV – Directional Design Hourly Volume; volume of vehicles in the design hour using the through lane adjacent to which the right lane is to be constructed.

Warrants for Right-Turn Lanes

Four Lane Roadways

Number of Peak Hour Turning Vehicles

DDHV (vph)

35 MPH or less

40 MPH

45 MPH

50 MPH

55 MPH

300

 

 

 

 

75

400

 

 

145

75

40

500

 

 

95

57

32

600

170

160

65

42

26

800

80

70

37

28

19

1,200

50

25

20

18

14

1,600

20

15

14

13

10

2,000

15

10

9

9

8

DDHV – Directional Design Hourly Volume; volume of vehicles in the design hour using the through lane adjacent to which the right lane is to be constructed.

Charts developed based on studies conducted by Kansas Department of Transportation and University of Nebraska.

Warrants for Left-Turn Lanes

Number of Peak Hour Turning Vehicles

DDHV

30 – 35 MPH

40 + MPH

100

30

14

200

15

12

300 +

12

12

(3)    Construction of turn lanes on State highways shall be determined in accordance with the State Access Code.

(4)    Dual left-turn lanes at signalized intersections shall be considered when the peak hour left-turn volume exceeds 300 vehicles/hour. An analysis of the signal timing is required to measure the effects of the protected movement on the rest of the intersection movements. Intersection geometry shall allow for the operation of dual lefts. Permissive dual left turns are prohibited.

(c)    Left- and Right-Turn Lane Design.

(1)    The components of a left-turn lane consist of a taper and the full width lane for storage as shown in the turn lane elements and design criteria. Turn lanes shall be 12 feet in width.

Minimum Left-Turn Tapers for Redirecting Through Lanes

Design Speed (MPH)

Tapers

25

10:1

30

15:1

35

20:1

40

30:1

45

45:1

50

50:1

55

55:1

60

60:1

    Based on Table 4-9 CDOT Access Code.

(2)    Use the same ratio for both approach and departure tapers.

(3)    Bay tapers shall be symmetrical reverse curves in accordance with the following:

(i)    Use 60-foot reverse curve for 25 to 35 miles per hour.

(ii)    Use 90-foot reverse curve for 40 to 50 miles per hour.

(iii)    Use 140-foot reverse curve for 55 to 65 miles per hour.

(4)    Storage lengths for turn lanes at signalized intersections shall be determined based on a signal timing analysis that predicts the 90 percent queue length required for the turn lane. At unsignalized intersections, the turn lane storage will be determined in accordance with the storage length table. Tapers for right-turn lanes shall be designed in accordance with the right-turn lane taper table. Use of the reverse curve is encouraged as part of the taper length to allow vehicles to decelerate in the full lane width. If used, the difference in length between the required taper and the reverse curve shall be added to the required storage length of the turn lane.

Minimum Storage Lengths for Unsignalized Turn Lanes

Turning VPH

≤60

100

200

300

Required Storage Length

50

100

175

250

Based on Table 9-7 CDOT Design Guide.

Minimum Right-Turn Tapers

Design Speed (MPH)

Tapers

25

7.5:1

30

8:1

35

10:1

40

12:1

45

13.5:1

50

15:1

55

18.5:1

60

25:1

    Excerpted from Table 4-6, CDOT Access Code.

(5)    Standards for State highway right-turn and left-turn speed change lanes are found in the State Access Code.

(Res. 39-04 (§ 6.2.5), 4-21-04)

29.28.180 Angles.

Proposed public streets must intersect at 90-degree angles or as close to 90 degrees as topography permits (no less than 80 degrees). Intersections on sharp horizontal curves shall be prohibited.

(Res. 39-04 (§ 6.2.6), 4-21-04)

29.28.190 Grades.

Intersections shall be on grades as flat as practical. At unsignalized intersections, the maximum allowable grade in the intersections is four percent and extends a minimum of 50 feet in each direction from the outside edge of the traveled way of the intersecting street. At signalized intersections, the maximum grade is two percent within the intersection and extends 200 feet in each direction. Grades above four percent will only be allowed on local and collector streets in areas with steep topography or other unusual circumstances that prevent a flatter grade, and must be documented as a design exception.

(Res. 39-04 (§ 6.2.7), 4-21-04)

29.28.200 Spacing and offsets.

(a)    Principal Arterials. Signalized intersections shall be spaced at one-half mile intervals. Unsignalized intersections must be T-intersections spaced at least 600 feet apart, measured centerline to centerline. Unsignalized four-legged intersections may be allowed on arterial streets; provided, that the design of the intersection precludes left turns onto and through movements across the arterial. If the overlap of left-turn storage requirements for two T-intersections exceeds 600 feet, the minimum spacing must be increased to provide adequate left-turn storage in both directions.

(b)    Minor Arterials and Collectors. Signalized intersections shall be spaced at one-quarter mile intervals. Unsignalized four-legged intersections must be spaced at least 300 feet apart. When T-intersections are used, the centerlines of streets not in alignment shall be offset a minimum of 150 feet and be 150 feet from the nearest four-legged intersection. If the left-turn storage requirements for adjacent intersections overlap, the minimum spacing must be increased to provide adequate left-turn storage in both directions.

(Res. 39-04 (§ 6.2.8), 4-21-04)

29.28.210 Pedestrian treatments.

Accommodations for pedestrians shall be designed into all intersections. Pedestrian accommodations include, but are not limited to, sidewalks, crosswalks, pedestrian refuge islands, and accommodations for disabled pedestrians. Sidewalks are an integral part of urban streets and shall be included in the intersection design. The City Standard Details shall be followed in designing and constructing pedestrian facilities. The intersection design shall conform to the standards set forth in the Americans with Disabilities Act. More information on the requirements can be found at http://www.access-board.gov/. Where sidewalks are provided, accessible ramps must also be provided. Utility boxes, drainage inlets, signs, and other fixed objects shall not be located within the path defined by ramp. The ramp shall align with the sidewalk and must be located entirely within the marked crosswalk area.

(a)    Crosswalks. Crosswalks shall be marked at signalized intersections and designed as part of the markings for the traffic signal. All crosswalk markings must conform to MUTCD standards. Crosswalks at unsignalized intersections or mid-block locations will only be considered when an engineering study is conducted in accordance with Institute of Traffic Engineers guidelines and indicates crosswalks would increase pedestrian safety.

(b)    Pedestrian Refuge Islands. Pedestrian refuge islands may be constructed where mid-block crosswalks are proposed. Islands must conform to the minimum standards established in the MUTCD, and must meet the design criteria for curbing and medians.

(Res. 39-04 (§ 6.2.9), 4-21-04)

29.28.220 Roundabouts.

(a)    Design Criteria.

(1)    A roundabout brings together conflicting traffic streams, allows the streams to safely merge and traverse the roundabout, and exit in the desired directions. The geometric elements of the roundabout provide guidance to drivers approaching, entering, and traveling through a roundabout.

(2)    Good roundabout design places a high priority on speed reduction and speed consistency. Low vehicle speed provides safety benefits including reduced numbers and severity of crashes; more time for entering drivers to judge, adjust speed for and enter a gap in circulating traffic; and safer merging. Roundabout intersections typically operate with lower vehicle delays than other intersection control types.

(3)    A capacity analysis of any proposed roundabout shall be conducted in accordance with Highway Capacity methods. The analysis shall include consideration for the largest motorized vehicle likely to use the intersection.

(4)    Roundabouts shall be designed in conformance with the guidelines set forth in the FHWA publication “Roundabouts: An Informational Guide.” The guide can also be found at http://www.tfhrc.gov.

(b)    Signing, Striping, and Pavement Markings. All signing, striping, and pavement markings shall follow the MUTCD standards.

(c)    Lighting. Adequate lighting is essential for drivers to perceive the general layout and operation of the intersection in time to make the appropriate maneuvers. A lighting plan will be required as part of the construction drawings for roundabouts.

(d)    Landscaping. Landscaping in the central island, the splitter islands and along the approaches is a benefit to both public safety and community enhancement. Landscaping shall follow these general principles:

(1)    Make the central island more conspicuous;

(2)    Improve the aesthetics of the area while complementing surrounding streetscaping as much as possible;

(3)    Avoid obscuring the form of the roundabout or the signing to the driver;

(4)    Maintain adequate sight distances;

(5)    Clearly indicate to the driver that they cannot pass straight through the intersection;

(6)    Discourage pedestrian movements through the center of the roundabout.

(Res. 39-04 (§ 6.3), 4-21-04)

29.28.230 Landscaping – General requirements.

All new developments must provide landscaping meeting the requirements of the City’s zoning and development code, GJMC 21.06.040, and the County’s Land Development Code, Chapter 7. Any landscaping in the sight distance triangles at intersections shall meet the sight distance requirements in the sight zones detail.

(Res. 39-04 (§ 6.4), 4-21-04)