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NMDOT - Route ID
Greg Olsen avatar
Written by Greg Olsen
Updated over a week ago

All roadways from interstate highways to unimproved trail roads are named with a field called Route ID. All New Mexico DOT route IDs in Numetric are unique numerical character strings that summarize all relevant data within the route, all separated by underscores. The Route IDs for each roadway follow specific criteria.

Route ID Meanings

All Routes, except Interchanges and Rest Areas, follow the following format (ex. I25P)

Route Prefix

Route Number

Route Suffix




Route Prefixes

Each route begins with a letter. Each prefix letter has a meaning.

  • I - Interstate - Interstate Signed Routes. New Mexico has three.

  • BL - Business Loop - Interstate Signed Business Loops. These routes are found in smaller cities and towns next to the interstates such as Santa Rosa, TorC, etc.

  • US - US Route - US Signed Routes

  • NM - NM State - State Signed Routes

  • FL - Federal Aid Local - Routes on the FHWA Federal Aid system that are not state-owned or maintained.

  • FR - Frontage Road - Routes that generally parallel major routes (I or US) that the NMDOT owns or maintains.

  • FS - Forest Service - Forest Service-owned Routes

  • FW - Fish and Wildlife Service - Department of Fish and Wildlife Service Routes

  • SP - State Park - Routes owned by the New Mexico State Parks Department. These routes are maintained by the NMDOT.

  • LOC - Local - Routes that are not state-owned or maintained and, are not on the federal aid system. This prefix accounts for the majority of the routes in the state.

  • STU - State Owned Unsigned - Unsigned State-Owned Routes

  • AI - Alternative Intersection - These routes are topological connectors and dedicated turn lanes that have a barrier between them and the mainline route and are not grade-separated. These are not true routes and have no data attached to them.

Route Numbers

Each Route is assigned a number. For the I, US, NM, and FR prefixed routes, these numbers are based on what is signed in the field such as US285 or I40. For the remainder of the routes, the numbers are random.

Route Suffixes

Each Route has either an M or P at its end.

  • P - Positive: This is the Primary direction of the route. The routes are digitized or “drawn” in this direction. If MilePosts are present on a route, the Positive direction is the increasing MilePost direction. If no MilePosts are present, we use the historical direction in which the routes were first digitized. For the rest of the routes, the P side generally goes from South to North and West to East but not always. On the NMDOT’s Linear Reference System, these routes contain most of the information regarding the road.

  • M - Minus: Minus side routes are created using FHWA guidance regarding minimum Dual Carriageway digitization. This guidance requires M-side routes where there is a four-foot separation and/or a physical barrier between the opposing directions of travel that exists for a minimum of 500 feet. As such, most M-suffixed routes are "dual-carriageway routes," However, the NMDOT also includes M sides on other roads that are not dual-carriageway. This is done on a case-by-case basis as needed by individual NMDOT Divisions such as Bridge locations and pavement collection on non-divided highways. As such determining whether a route is single or dual carriageway solely based on a route having a M suffix is NOT recommended. M-side routes do not carry as much roadway data as the P-side of a road.

A note on Route ID measures:

Every route has a beginning and end measure. Routes from NMDOT’s Linear Reference System use “MilePoints.” This is similar to a MileMarker which is the sign the NMDOT places next to the road. MilePoints are highly accurate and can change when a road is realigned, roads are transferred, ETC. MileMarkers generally are not highly accurate and do not get updated and thus, may not represent the true measure of a route.

The MilePoint numbering of M side routes mirrors the P side, i.e.: MileMarker/Point 0 on I40 for both P and M starts at the Arizona state line and increases as you go east.

Interchange and Rest Area Route IDs

Grade-separated Interchanges and Rest Areas Route IDs. (ex. IX25P003.0A)

Route Prefix

Route Number

Route Suffix








Route Prefix

For Ramps this letter represents the mainline route prefix with an "X" attached to it: IX. For Rest Areas an RA is put in front of the mainline route prefix: RAI.

Route Number

This is the number of mainline routes the interchange or rest area serves.

Route Suffix

All Interchange and Rest Areas are "P" routes.


For grade-separated interchanges only. These are the individual ramp leg coded as the one nearest the parent route (A,G,N,T) fo furthest from the parent route (D,J,Q,W). Note that “+” means the positive or “P” side of the route and “-“indicates the minus or “M” side of the route.

  • A - A - First Off-Ramp In + Dir

  • B - B - Second Off-Ramp On The + Dir

  • C - C - Third Off-Ramp On The + Dir

  • D - D - Fourth Off-Ramp On The + Dir

  • G - G - First On-Ramp In + Dir

  • H - H - Second On-Ramp On The + Dir

  • I - I - Third On-Ramp On The + Dir

  • J - J - Fourth On-Ramp On The + Dir

  • N - N - First Off-Ramp In - Dir

  • O - O - Second Off-Ramp On The - Dir

  • P - P - Third Off-Ramp On The - Dir

  • Q - Q - Fourth Off-Ramp On The - Dir

  • T - T - First On-Ramp In - Dir

  • U - U - Second On-Ramp On The - Dir

  • V - V - Third On-Ramp On The - Dir

  • W - W - Fourth On-Ramp On The – Dir

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