Existing Environmental Conditions
At the onset of this study, the existing environmental conditions within the project area were assessed. The primary objectives of the existing conditions assessment were to describe key features of the project area and to identify the salient conditions that warrant consideration as alternatives are developed and evaluated. Existing conditions were identified based on field reconnaissance and a review of existing data and records. The existing environmental conditions are separated into natural resources, cultural resources, and community and economic resources.
Roadway Cross Section
The existing typical for most of the project except the central business district (CBD) is two 12-foot driving lanes with wide undefined shoulders. The CBD: from Sunset Avenue to Railroad Avenue, consists of 80-feet of pavement, which accommodates two-travel lanes separated with double-yellow solid stripes, and undefined angled parking. Raised 10-foot wide sidewalks intermittently line both sides of the roadway as frontage for commercial properties. The right-of-way (R/W) is estimated to be along the building frontages, many of which have awnings which likely encroach.
The US 60 corridor through Mountainair and through the project limits is comprised of four segments, the first segment, beginning at MP 203.6 (BOP) and going east to the intersection with Forest Avenue, just east of MP 204. The intersections in this segment approach US 60 at a 60º skew creating acute intersections, which tend to limit visibility and need extensive turning roadway areas. Residents and business along this segment are aligned with the highway and generally have perpendicular access points. The second segment, located between Forest Avenue and Summit Avenue (MP 204.342), consists of reverse curves which change the highway’s northeast/southwest alignment to an east/west alignment along Mountainair’s Broadway. US 60 intersects 3rd Street, and Corbett Avenue, consuming Corbett Avenue’s footprint north of the intersection, and creating a five-leg intersection. North of this intersection US 60 crosses main street at nearly 90º and does not seem to have geometric issues related to the intersection. North Main Street US 60 provides access to a former alley which has been widened out but remains unnamed. The alley intersects US 60 at about the midpoint of a right-hand horizontal curve and forms an acute
The US 60 MP 203 TO 205 corridor currently contains most of the allowable access per the NMDOT State Access Management Manual (SAMM). Much of the corridor is currently undeveloped; therefore, the amount of existing access should be reduced. This reduction may result from consolidation of access by providing joint access or single access driveways for small developments. Median openings have proliferated within the corridor and there are 250% of the allowable openings per the standards, indicating a needed reduction. None of the access locations has speed change lanes in accordance with the SAMM and this need should be addressed, especially for median openings. Access needs to be managed to maintain good operations and safety.
The terrain is relatively flat generally sloping from east to west. Stormwater drains from east to west in arroyos with the largest arroyo being La Luz Creek. These arroyos originate in the Sacramento Mountains to the east and flow into the Tularosa Basin.
Drainage basins for structures within the project area lie to the east of US 60 MP 203 TO 205, initiating from the Sacramento Mountains, and flow in a southwesterly direction. Due to the proximity to the foothills of the Sacramento Mountains, the project area experiences heavy storms and frequent peak flows.
A total of 54 cross drainage structures were identified within the project limits. All existing culverts are in good structural condition though inlet and outlet sedimentation are issues at a majority of the structures. Seven (7) of the existing culverts were found to be inadequate and need to be replaced with larger structures or have additional structures installed.
Various developments both upstream and downstream of the exiting drainage structures have changed the historic drainage patterns. Many of the smaller drainage crossings are partially silted and not functional since their outlet channels have been diminished. Presence of alluvial fans, formed where fast flowing waters from the Sacramento Mountains spread onto flatter plains, cause considerable sedimentation and scouring issues at the existing drainage structures in the study area. Some of the larger drainage crossings have experienced scour at their outlets. As much as nine feet of scour was measured at the outlet of the existing 4-10’x12’ concrete box culverts (CBC’s) at MP 73.6; currently no erosion control measures exist at the outlet of this structure.
An 1800-foot long dike, presumably constructed by the adjoining property owner, along the east side of the highway and north of milepost 75, diverts the flow that used to get to the drainage crossing at milepost 75.2, in a southerly direction to the drainage crossing at milepost 74.9.
Existing twin bridges (Bridge numbers 2560-SBL and 5743-NBL) at milepost 72.6; spanning La Luz Creek are both scour critical. Bridge number 2560 was built in 1932 with a sufficiency rating of 42.2 and Bridge number 5743 was built in 1957 with a sufficiency rating of 78.9. Considerable channel degradation has occurred at this location. In the late nineties, the NMDOT constructed a gabion drop structure just downstream of these twin bridges and filled the channel under the bridges with derrick stone in an effort to control the head cut from migrating upstream. Local scour is still taking place and the gabion drop structure is being undermined.
Considerable effort has been made by the NMDOT to install guardrail to shield the ends of the existing concrete box culverts. The end treatments for a number of smaller crossing structures and the existing median drop inlets along the corridor do not meet the latest NMDOT specifications.
Mr. Kevin Norman, the Patrol Supervisor for the project area, was also contacted during the inspection and he highlighted the following three areas of concern.
MP 74.0-74.5 – Roadway overtopping and flooding occur regularly along this half mile stretch of US 60 MP 203 TO 205.
MP 74.8 – Roadway overtopping and flooding have been a problem at this location. Modifications to the downstream channel have helped to alleviate some of the drainage issues.
MP 77.5 – The existing 6-10’x7’ CBC’s appear to be undersized as roadway overtopping occurs during minor
rainfall events. Water backs up from the structure inlet to the roadway sign just north of the structure. Hundreds of yards of fill have been brought in to manage erosion of the upstream channel.
Drainage Recommendations are included in the Appendix.
Geology and Soils
Soils throughout the alignment area appear to consist of a combination of reddish-brown sandy clays (CL), silty-sandy clay (CL-ML) and silty sands (SM). The sands appeared to be predominantly fine grained. Gravels were relatively rare and appeared mostly on the ground surface. Bedrock was not observed during our reconnaissance. Gypsum may be present but was not readily apparent during our reconnaissance. The site reconnaissance and literature review conducted during this study did not identify areas within the proposed alignment that will prevent or seriously affect project development. The sandy and silty soils should be of sufficient strength for use as road subgrade. The sandy clay soils may require improvement or replacement. Proper moisture conditioning and compaction will be required and some settlement and subgrade problems may occur in any of the soils encountered in our reconnaissance. High plasticity soils should be treated or removed and replaced with high quality fill soil. Blasting will probably not be required and ripping, if required, should be limited to local exposures of the Santa Fe Group. Proximity to arroyos from the nearby Sacramento Mountains to the east could be an indication of potentially collapsible soils.
The proposed alignment will be bounded by U.S. 82 in Alamogordo on the south and Radio Road in Tularosa on the north, and will be constructed along existing embankments and across arroyos, requiring substantial cuts and fills. Foundations for retaining walls and/or culverts are not anticipated to require use of deep foundations. The La Luz Creek Bridge(s) may require deep foundations. Investigations should include some moderately deep borings (i.e. approximately 50 to 80-feet deep) for approach embankments, retaining walls or any structures. Geotechnical and Foundation investigations should characterize shear strength and compressibility of subgrade and foundation soils. These borings should also characterize the "stability" of drilled shaft holes installed in loose, unsaturated soils. The geotechnical and Foundation investigations should address corrosive properties of the soils. Proximity to the Alamogordo Fault warrants a geophysical study along the alignment.
The existing pavement was observed to be in generally good condition throughout the alignment with relatively minor transverse cracking about ¼-inch in width. Increased cracking (longitudinal and transverse) was observed approximately 650 feet of roadway north and south of the La Luz Gate intersection. The majority of the observed cracks were sealed, an indication of good maintenance practices throughout the alignment. Since the mid-1990’s there has been several pavement preservation projects conducted through the corridor including: cold recycling existing pavement and overlay and milling existing pavement and inlay.
The posted speed limit on existing US 60 MP 203 TO 205 varies from 55 mph from mile markers 70.05 to 72.1 where the posted speed increases to 60 mph. There are reduced speeds to 45mph at the BOP approach to the US 82/Alamogordo Relief Route intersection, the La Luz Gate intersection and mile marker 77.8 just south of Bookout Rd./Radio Rd. intersection.
The existing right of way (ROW) is 200 feet through the corridor. The roadway is off centered to the west and some of the steeper slopes are already very close to the existing ROW line. Flattening slopes and extending structures outside the clear zone will result in a need for additional ROW. These issues may be mitigated with properly designed roadside barriers.
Preliminary Property Ownership
The property adjacent to the existing alignment is privately owned with the exception of four (4) parcels one which is owned by Otero County at mile marker 70.8, two owned by BLM at mile markers 70.9 and 75.6 and a parcel owned by NMDOT at Tumbleweed Road (Tularosa Maintenance Patrol Yard).
Utilities that exist along the corridor include water, gas, fiber optic and power transition lines. Subsurface Utility Engineering (SUE) Quality Level B services will provide locations of underground and above ground utilities that may be affected with any of the construction alternates.
The existing fence varies from chain link to wooden rail and steel cable at some businesses. The more rural areas have barbed wire, some with wooden posts and some with metal posts. Condition of existing fencing varies throughout the corridor. Most of the existing fence should be replaced. Replacement should be evaluated on a project by project basis. There was at least one comment by a citizen that fence should be replaced.
The project area has a total of seven drainage structures crossing the roadway. One is a major structure and the rest are various size drain culverts. None of these structures have any type of barrier protection installed. End treatments are inadequate, and some are missing at the outlets. Silting is a major problem reducing capacity for most of the culverts. All structures will need to be reconditioned or replaced to ensure proper flow. Extensions will be required in order to have enough room for barrier to be installed.
The clear zone for this project varies with speed and slope. Traffic volumes are above 6000 ADT.
The clear zone for 45 mph is:
Slope Clear Zone
6:1 or flatter 32 feet
5:1 – 4:1 36 to 44 feet
The clear zone for 40 mph is:
Slope Clear Zone
6:1 or flatter 24 feet
5:1 – 4:1 26 to 32 feet
The clear zone for 30 mph is:
Slope Clear Zone
6:1 or flatter 24 feet
5:1 – 4:1 26 to 32 feet