N.M. Admin. Code § 18.31.6.17 - SPEED-CHANGE LANE REQUIREMENTS

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.

Notes

N.M. Admin. Code § 18.31.6.17

18.31.6.17 NMAC - Rp, 18 NMAC 31.6.12.7.1 through 18 NMAC 31.6.12.7.6, 10/15/2001, Adopted by New Mexico Register, Volume XXVIII, Issue 12, June 27, 2017, eff. 6/27/2017