New Mexico Administrative Code
Title 18 - TRANSPORTATION AND HIGHWAYS
Chapter 31 - CLASSIFICATION AND DESIGN STANDARDS FOR HIGHWAYS
Part 6 - STATE HIGHWAY ACCESS MANAGEMENT REQUIREMENTS
Section 18.31.6.17 - SPEED-CHANGE LANE REQUIREMENTS

Universal Citation: 18 NM Admin Code 18.31.6.17

Current through Register Vol. 35, No. 6, March 26, 2024

A. Purpose: This section defines the criteria for determining where speed-change lanes are required along non-access controlled and controlled-access state highways that provide access via at-grade intersections. Application guidelines for speed-change lanes on controlled-access interstate highways and freeways, which provide access exclusively by grade-separated interchanges, are also provided; however, specific criteria for speed-change lanes on grade-separated highway facilities are not explicitly defined (see Subsection C of 18.31.6.17 NMAC).

B. State highways with at-grade intersections: At unsignalized at-grade intersections, four types of speed-change lanes are used including left-turn deceleration lanes, right-turn deceleration lanes, left-turn acceleration lanes, and right-turn acceleration lanes. At signalized at-grade intersections, three types of speed-change lanes are used including exclusive left-turn lanes, exclusive right-turn lanes, and right-turn acceleration lanes.

(1) Schematic illustrations: Illustrations of left-turn and right-turn speed-change lanes can be found in the appendix of the state access management manual.

(2) Design period: The need for speed-change lanes should be assessed using the hourly traffic volumes derived for the traffic study implementation year with the proposed development, or based on the future year traffic forecasts developed for a highway improvement project.

(3) General criteria:
(a) Speed-change lanes may be required by the department at unsignalized or signalized access points where specific public safety and traffic operation concerns are identified and documented.

(b) Left-turn acceleration and deceleration lanes should not overlap. Preference should be given to the left-turn deceleration lane. Alternative treatments to providing a left-turn acceleration lane may be considered when this situation arises such as providing traffic signal control or restricting the left-turn movement from the cross street. Alternative treatments require approval by the district traffic engineer.

(c) Where two access points have right-turn speed-change lanes that overlap, or are in close proximity but do not overlap, a continuous ingress/egress lane may be established between the access points to improve roadway consistency, safety, and to maintain roadway edge continuity.

(d) If the design of an access facility crosses two different speed zones, the speed-change lane design should be based upon the applicable speed limit. The applicable speed for a deceleration lane is the posted speed limit at the beginning of the deceleration lane. The applicable speed for an acceleration lane is the posted speed limit at the end of the acceleration lane.

(e) Acceleration lanes should only be used where sufficient acceleration length can be provided.

(f) On multi-lane highways, the directional hourly traffic volume, or directional split, should be determined based on actual traffic count data. It may be assumed that traffic is equally divided among the mainline travel lanes when traffic count data are not available.

(4) Unsignalized Intersections: In addition to the location of the roadway (urban or rural), the three primary factors used to determine the need for a speed-change lane at an unsignalized at-grade access are highway travel speed, directional traffic volume per lane, and turning traffic volume. Sight distance conditions, level of service, and roadway geometry should also be examined when determining the need for speed-change lanes.
(a) Urban conditions: The need for left-turn and right-turn deceleration lanes on urban state highways should be determined based on the criteria in tables 17.B-1 and 17.B-2. right-turn acceleration lanes may be required on urban state highways with posted speed limits greater than 40 mph where an acceleration lane is necessary for public safety and traffic operations based upon site and roadway specific conditions. Left-turn acceleration lanes may be required on urban state highways with posted speed limits greater than 45 mph where an acceleration lane is necessary for public safety and traffic operations based upon site and roadway specific conditions.

(b) Rural conditions: The need for left-turn and right-turn deceleration lanes on rural state highways should be determined based on the criteria in tables 17.B-3 through 17.B-6. right-turn acceleration lanes may be required on rural state highways with posted speed limits greater than 40 mph where an acceleration lane is necessary for public safety and traffic operations based upon site and roadway specific conditions. Left-turn acceleration lanes may be required on rural state highways with posted speed limits greater than 45 mph where an acceleration lane is necessary for public safety and traffic operations based upon site and roadway specific conditions.

(5) Signalized intersections: The use of speed-change lanes at signalized intersections is generally consistent for all access categories, urban and rural. Guidelines for determining the need for speed-change lanes at signalized intersections can be found in Section 17 of the state access management manual.

C. State and interstate highways with grade-separated interchanges: Speed-change lanes are used on controlled-access state and interstate highways at or between grade-separated interchanges. The need for speed-change lanes on grade-separated highway facilities should be determined based on design principles contained in the AASHTO publication a policy on geometric design of highways and streets, and based on detailed traffic operations analyses of the grade-separated facilities according to highway capacity manual methodologies. The need for and function of speed-change lanes should be documented in an interchange access management plan for the interchange (refer to 18.31.6.12 NMAC). Speed-change lanes on grade-separated highway facilities should enable a driver to make the necessary transition between the speed on a ramp and the speed of operation on the mainline highway in a safe and functional manner. Additional guidance is provided in Section 17 of the state access management manual.

Table 17.B-1

Criteria for Deceleration Lanes On

Urban Two-lane Highways

Turning Volume (vph)

LEFT-TURN DECELERATION LANE

RIGHT-TURN DECELERATION LANE

Minimum Directional Volume in the Through Lane (vphpl) 2

Minimum Directional Volume in the Through Lane (vphpl) 2

[] 30 mph

35 to 40 mph

45 to 55 mph

[] 30 mph

35 to 40 mph

45 to 55 mph

[] 5

Not Required

Not Required

Not Required

Not Required

Not Required

Not Required

5

510

450

330

1,080

610

360

10

390

330

210

700

400

240

15

320

250

150

500

280

170

20

270

200

120

380

210

140

25

230

160

100

300

180

120

30

200

130

Required

250

160

110

35

170

110

Required

220

150

100

40

150

Required

Required

200

140

Required

45

130

Required

Required

190

Required

Required

[] 46

Required

Required

Required

Required

Required

Required
Left-turn Deceleration Lanes are required on Urban Two-lane Highways for the following Left-turn Volumes: Right-turn Deceleration Lanes are required on Urban Two-lane Highways for the following Right-turn Volumes:

1. [] 30 mph : 46 vph or more

2. 35 to 40 mph : 36 vph or more

3. 45 to 55 mph : 26 vph or more

4. [] 30 mph : 46 vph or more

5. 35 to 40 mph : 41 vph or more

6. 45 to 55 mph : 36 vph or more

Notes:

1. Use linear interpolation for turning volumes between 5 and 45 vph.

2. The directional volume in the through lane includes through vehicles and turning vehicles.

Table 17.B-2

Criteria for Deceleration Lanes on

Urban Multi-lane Highways

Turning

Volume 1

(vph)

LEFT-TURN DECELERATION LANE

RIGHT-TURN DECELERATION LANE

Minimum Volume in the Adjacent Through Lane (vphpl) 2

Minimum Volume in the Adjacent Through Lane (vphpl) 2

[] 30 mph

35 to 40 mph

45 to 55 mph

[] 30 mph

35 to 40 mph

45 to 55 mph

[] 5

Not Required

Not Required

Not Required

Not Required

Not Required

Not Required

5

Not Required

490

420

1,200

730

450

10

420

370

300

820

490

320

15

360

290

220

600

350

240

20

310

230

160

460

260

180

25

270

190

130

360

230

150

30

240

160

110

290

200

130

35

210

130

100

260

180

120

40

180

120

Required

240

170

110

45

160

110

Required

220

160

Required

50

140

Required

Required

200

Required

Required

55

120

Required

Required

190

Required

Required

[] 56

Required

Required

Required

Required

Required

Required
Left-turn Deceleration Lanes are required on Urban Multi-lane Highways for the following Left-turn Volumes: Right-turn Deceleration Lanes are required on Urban Multi-lane Highways for the following Right-turn Volumes:

3. [] 30 mph : 56 vph or more

4. 35 to 40 mph : 46 vph or more

5. 45 to 55 mph : 36 vph or more

6. [] 30 mph : 56 vph or more

7. 35 to 40 mph : 46 vph or more

8. 45 to 55 mph : 41 vph or more

Notes:

1. Use linear interpolation for turning volumes between 5 and 55 vph.

2. The volume in the adjacent through lane includes through vehicles and turning vehicles.

Table 17.B-3

Criteria for Left-Turn Deceleration Lanes on

Rural Two-lane Highways

Left-Turn Volume 1 (vph)

LEFT-TURN DECELERATION LANE

Minimum Directional Volume in Through Lane (vphpl) 2

[] 30 mph

35 to 40 mph

45 to 55 mph

[] 55 mph

[] 5

Not Required

Not Required

Not Required

Not Required

5

400

220

120

60

10

240

140

80

40

15

160

100

60

Required

20

120

80

Required

Required

25

100

Required

Required

Required

³ 26

Required

Required

Required

Required
Left-turn Deceleration Lanes are required on Rural Two-lane Highways for the following Left-turn Volumes:

1. [] 30 mph : 26 vph or more

2. 35 to 40 mph : 21 vph or more

3. 45 to 55 mph : 16 vph or more

4. [] 55 mph : 11 vph or more

Notes:

Use linear interpolation for left-turn volumes between 5 and 25 vph.

The directional volume in the through lane includes through vehicles and turning vehicles.

Table 17.B-4

Criteria for Left-turn Deceleration Lanes on

Rural Multi-lane Highways

Left-Turn Volume 1 (vph)

LEFT-TURN DECELERATION LANE

Minimum Volume in Adjacent Through Lane (vphpl) 2

[] 30 mph

35 to 40 mph

45 to 55 mph

[] 55 mph

[] 5

Not Required

Not Required

Not Required

Not Required

5

450

310

210

130

10

310

220

130

90

15

240

160

100

70

20

190

130

80

Required

25

150

110

Required

Required

30

130

Required

Required

Required

35

110

Required

Required

Required

[] 36

Required

Required

Required

Required
Left-turn Deceleration Lanes are required on Rural Multi-lane Highways for the following Left-turn Volumes:

5. [] 30 mph : 36 vph or more

6. 35 to 40 mph : 26 vph or more

7. 45 to 55 mph : 21 vph or more

8. [] 55 mph : 16 vph or more

Notes:

1. Use linear interpolation for left-turn volumes between 5 and 35 vph.

2. The volume in the adjacent through lane includes through vehicles and turning vehicles.

Table 17.B-5

Criteria for Right-Turn Deceleration Lanes on

Rural Two-lane Highways

Right-Turn Volume 1 (vph)

RIGHT-TURN DECELERATION LANE

Minimum Directional Volume in Through Lane (vphpl) 2

[] 30 mph

35 to 40 mph

45 to 55 mph

[] 55 mph

[] 5

Not Required

Not Required

Not Required

Not Required

5

800

460

270

160

10

430

280

170

110

15

290

180

110

80

20

200

140

90

70

25

170

120

80

Required

30

160

110

Required

Required

[] 31

Required

Required

Required

Required

Right-turn Deceleration Lanes are required on Rural Two-lane Highways for the following Right-turn Volumes:

3. [] 30 mph : 31 vph or more

4. 35 to 40 mph : 31 vph or more

5. 45 to 55 mph : 26 vph or more

6. [] 55 mph : 21 vph or more

Notes:

1. Use linear interpolation for left-turn volumes between 5 and 30 vph.

2. The directional volume in the through lane includes through vehicles and turning vehicles.

Table 17.B-6

Criteria for Right-Turn Deceleration Lanes on

Rural Multi-lane Highways

Right-Turn Volume 1 (vph)

RIGHT-TURN DECELERATION LANE

Minimum Volume in Adjacent Through Lane (vphpl) 2

[] 30 mph

35 to 40 mph

45 to 55 mph

[] 55 mph

[] 5

Not Required

Not Required

Not Required

Not Required

5

910

520

310

180

10

520

330

200

130

15

370

220

140

100

20

270

170

110

90

25

220

140

100

Required

30

200

130

90

Required

35

180

120

Required

Required

[] 36

Required

Required

Required

Required

Right-turn Deceleration Lanes are required on Rural Multi-lane Highways for the following Right-turn Volumes:

3. [] 30 mph : 36 vph or more

4. 35 to 40 mph : 36 vph or more

5. 45 to 55 mph : 31 vph or more

6. [] 55 mph : 21 vph or more

Notes:

1. Use linear interpolation for left-turn volumes between 5 and 35 vph.

2. The volume in the adjacent through lane includes through vehicles and turning vehicles.

Disclaimer: These regulations may not be the most recent version. New Mexico may have more current or accurate information. We make no warranties or guarantees about the accuracy, completeness, or adequacy of the information contained on this site or the information linked to on the state site. Please check official sources.
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