The St. Francis/St. Michaels Interchange Study (Study) in Santa Fe, New Mexico is sponsored by the NMDOT with funding from the Federal Highway Administration. The Study is centered on the St. Francis/St. Michaels Interchange, including St. Francis Drive (US 84-285) from Siringo Road to San Mateo Road and along St. Michaels Drive (NM 466) from Pacheco Street to Galisteo Street (see vicinity map). The current Study is a continuation of the previous St. Francis/St. Michaels – Interchange Alternatives Report (Phase A), which was an initial screening evaluation to define purpose and need, identify alternative design solutions, and determine which were unfeasible and should be eliminated from further consideration. The current Phase B Detailed Evaluation of Alternatives will evaluate the remaining alternatives in greater detail and make recommendations for a preferred alternative.
The PURPOSE of the current Study is to address physical, operational, and safety deficiencies and to enhance pedestrian and bicycle connectivity through the Interchange area. Specific NEEDS to be identified include:
- Roadway: No merge lanes are provided on St. Francis Dr. at three existing on ramp locations. There is limited separation distance between existing ramp terminals and the West San Mateo and Galisteo Street intersections. Pavement is deteriorating along St. Francis Dr. and St. Michaels Dr. and drainage infrastructure needs repair.
- Bridge 7336: The 45-year old St. Francis Dr. Bridge has a substandard load rating, deficient load carrying capacity, low structural evaluation and sufficiency ratings, and is classified as “Structurally Deficient” and “Functionally Obsolete”. The limited deck width prohibits a merge lane from the existing cloverleaf on-ramp and the concrete box girder superstructure is not considered a good candidate for rehabilitation.
- Multi-Modal Facilities: East-west and north-south connectivity for pedestrians and bicycles is constrained throughout the interchange area. Transit services utilize and travel through the area.
- Localized congestion issues include deficient storage length at the existing cross street intersections where traffic queues extend beyond available storage areas and spill over into adjacent traffic lanes.
- Under future travel demand conditions, queue lengths are expected to increase, exasperating existing problem areas and resulting in potential new locations of queue spillback.
- A high number of crashes within the interchange occur at four locations: 1). the southbound off-ramp/St. Michaels Dr. intersection, 2). the southbound on-ramp to St. Francis Dr., 3). eastbound St. Michaels Drive between the northbound off-ramp and Galisteo Street, and 4). the west to northbound on-ramp to St. Francis Dr. (view summary)
- Two additional hot spots were identified: 5). the stop-controlled intersection at the northbound off-ramp and 6). St. Michaels Dr. and the northbound loop on-ramp to St. Francis Dr.
- A higher than expected crash frequency was identified at the four signalized cross street intersections adjacent to the interchange area.
- Three pedestrian crashes have occurred within the Study area. (view summary)
The previous St. Francis/St. Michaels Interchange Alternatives Report identified nine alternatives, including the No Build Alternative, and evaluated their comparative benefits and disadvantages. Performance was assessed in several key areas, including physical deficiencies, traffic operations, safety, bicycle and pedestrian improvements, constructability and management of traffic, and project costs. Based on initial screening evaluation, the following alternatives were fount to be less feasible:
- Re-stripe Existing St. Francis Drive: The Re-Striping Alternative would return the travel lane configuration along St. Francis Drive, from Siringo Road to West San Mateo, to the four lane configuration that existed before 2005 (view map).This would efficiently address the prominent merge lane deficiency that currently exists at the three on-ramps entering St. Francis Dr.; however, many deficiencies (e.g. physical, operational, safety, and multimodal) would remain and the new lane drops on St. Francis Dr. could induce operational and safety concerns.
- Modern Roundabout: This alternative would replace the existing bridge and interchange with an at-grade modern roundabout (view map). Although it addresses project needs, the roundabout would pose multi-lane complexity and driver expectancy/familiarity concerns and result in operational deficiencies under 2035 conditions.
- Single Point Urban Interchange (SPUI): This alternative would convert the existing interchange into a SPUI, with all on and off-ramp connections on St. Michaels consolidated into a single signalized intersection (view map). The SPUI would address the Study purpose and need but would have significant impacts to traffic during construction and a high cost relative to other alternatives.
- Diverging Diamond Interchange (DDI): This alternative would convert the existing interchange into a DDI, with mainline eastbound and westbound traffic on St. Michaels Dr. “crossed over” to eliminate left turn phases at the signalized ramp intersections (view map). The DDI alternative would address purpose and need but would result in an anticipated increase in crashes, severe impacts to traffic during construction, higher costs, and additional right-of-way requirements along St. Michaels Dr.
The Study Team would like to advance the following alternatives for more detailed evaluation:
- No-Build: The No-Build Alternative provides a basis upon which each of the initial build alternatives for the proposed interchange improvement project can be compared. This alternative would have no project-related impacts but does not address any physical, operational bicycle/pedestrian, or safety related deficiencies.
- Signalized Intersection: This alternative would replace the existing bridge and interchange with a conventional at-grade intersection at St. Francis Dr. and St. Michaels Dr. (view map). The Signalized Intersection Alternative addresses Study purpose and need and provides for an at-grade alternative for comparison with interchange alternatives.
- Diamond Interchange: This alternative would convert the existing half diamond interchange into a full diamond configuration maintaining the grade separation of St. Francis Dr. over St. Michaels Dr. (view map). The Diamond Interchange addresses Study needs and provides a greater range of potential benefits compared to other alternatives.
- Ramp Reconfiguration: The Ramp Reconfiguration Alternative would improve the on- and off-ramps on the east side of the interchange, replacing the two existing northbound on-ramps with a single “trumpet” style ramp (view map). This alternative addresses Study needs and provides greater potential benefits compared to other alternatives.
- Split Bridge Northbound/Southbound Left-on Access: This alternative would convert the existing interchange into a split bridge configuration, with the St. Francis Dr. mainline split to cross over St. Michaels Dr. on two new structures. On-ramps from St. Michaels Dr. would access St. Francis Dr. on the left (view map). It addresses project needs and provides greater benefits compared to other alternatives, but requires an unconventional left-merge for the St. Michaels Dr. to St. Francis Dr. on-ramps.