Gauge face wear is metal lost from the inside face of the rail head, where wheel flanges rub on curves and at switches. FRA's 49 CFR Part 213 sets no gauge face wear limit. It limits track gage (56 to 57½ in. on Class 4 and 5 track), so wear limits come from railroad standards and AREMA recommended practice.
That split is the key to reading any wear measurement. A rail can be badly side-worn while the track still meets the federal gage limit, and wear that is legal under Part 213 can still raise wheel-climb risk and make ultrasonic rail testing less reliable.
This guide covers how side wear forms, exactly what Part 213 does and doesn't regulate, how wear is measured, how the gauge face angle links to wheel climb, and why head wear matters to a rail flaw test.
What is gauge face wear on rail?
Gauge face wear (also called side wear) is metal lost from the gauge side of the rail head, measured horizontally from the original new-rail profile. It forms where the wheel flange contacts the rail, so it is heaviest on the high (outer) rail of curves, on stock rails and switch points in turnouts, and anywhere the flange works hard.
FRA's rules spell the word "gage"; most railroad and research documents spell it "gauge". They mean the same thing.
| Term | What it describes | Usual reference point |
|---|---|---|
| Gauge face | The inside vertical face of the rail head, toward the track center | — |
| Gauge face wear (side wear) | Horizontal loss of metal from the gauge face | Commonly read at the gage line, 5/8 in. below the top of rail |
| Head height loss (vertical wear) | Loss of metal from the running surface | Top of rail at the head centerline |
| Gauge face angle | The angle between the worn gauge face and the vertical | Over a defined band of the gauge face |
| Track gage | The distance between the two rail heads | 5/8 in. below the top of rail (213.53) |
Several things drive the rate of side wear: curvature and the wheelset's angle of attack, lateral wheel force, wheel profile, and friction at the flange. Gauge face lubrication and other friction management reduce flange wear, which is why railroads lubricate the high rail of sharp curves.
Key takeaway: side wear, head height loss and gauge face angle are three different measurements of the same worn rail head, and each answers a different question.
Does FRA Part 213 set a gauge face wear limit?
No. The FRA Track Safety Standards (49 CFR Part 213) contain no limit on rail head wear or side wear for running rail. We confirmed this by searching the full text of Part 213 in the annual CFR XML on govinfo (Title 49, volume 4, revised as of October 1, 2024). The terms "side wear", "head wear", "rail wear" and "gage corner" don't appear, and "wear" appears only three times, none of them about the rail head.
What Part 213 does regulate near this topic is listed below.
| Part 213 section | What it says that touches wear | Is it a rail wear limit? |
|---|---|---|
| 213.53 Gage | Minimum and maximum track gage by class, measured 5/8 in. below the top of the rail head | No. It limits the result (gage), not the wear |
| 213.110 Gage restraint measurement systems | Optional loaded-gage testing for crosstie and fastener compliance | No |
| 213.115 Rail end mismatch | Mismatch on the gage side of rail ends: 1/8 in. on Class 4 and 5 | No. It applies at joints |
| 213.121(b) Rail joints | A joint bar that "because of wear" allows excessive vertical movement must be replaced (Class 3 to 5) | No. It is about joint bars |
| 213.135(h) Switches | "Unusually chipped or worn switch points shall be repaired or replaced" | No number is given |
| 213.137(b)(c) Frogs | 10 mph if a frog point is worn more than 5/8 in. down and 6 in. back, or a frog tread is worn more than 3/8 in. below the original contour | It is a frog limit, not a running-rail limit |
| 213.141 Self-guarded frogs | The raised guard may not be worn more than 3/8 in. | Frogs only |
| 213.113 Defective rails | Lists rail defects such as flattened head; worn rail is not one of them | No |
Two consequences follow. First, any web page that quotes an "FRA gauge face wear limit" is quoting something else, usually a railroad's own standard. Second, side wear can still produce a Part 213 deviation indirectly, by widening the track gage past the 213.53 limit or through switch-point condition under 213.135(h).
Part 213 is also a floor: section 213.1(a) sets minimum requirements, and a track owner can adopt stricter ones. Rail transit not connected to the general railroad system is outside Part 213 (213.3(b)) and falls under state safety oversight, which in California is the CPUC.
Key takeaway: the honest answer to "what is the FRA side wear limit?" is that there isn't one; FRA regulates the gage the wear produces.
What are the FRA gage limits by track class?
Section 213.53 limits track gage between 56 in. and 57½ in. on Class 4 and 5 track, with wider maximums on lower classes. The rule defines where gage is read:
"Gage is measured between the heads of the rails at right-angles to the rails in a plane five-eighths of an inch below the top of the rail head." (49 CFR 213.53(a))
| Class of track | Gage at least | Gage not more than | Source |
|---|---|---|---|
| Excepted track | N/A | 4 ft 10¼ in. (58¼ in.) | 213.53(b) |
| Class 1 | 4 ft 8 in. (56 in.) | 4 ft 10 in. (58 in.) | 213.53(b) |
| Class 2 and 3 | 4 ft 8 in. | 4 ft 9¾ in. (57¾ in.) | 213.53(b) |
| Class 4 and 5 | 4 ft 8 in. | 4 ft 9½ in. (57½ in.) | 213.53(b) |
| Class 6, 7 and 8 | 4 ft 8 in. | 4 ft 9¼ in. | 213.323 |
| Class 9 | 4 ft 8¼ in. | 4 ft 9¼ in. | 213.323 |
Class 6 to 9 track also limits the change of gage within 31 ft (¾ in. on Class 6, ½ in. on Classes 7 to 9). Standard gage is 4 ft 8½ in. (56½ in.), so on Class 4 and 5 track there is only 1 in. between nominal and the federal maximum.
Worked example: how side wear uses up gage margin
The gage line sits 5/8 in. below the top of rail, and side wear is usually read at that same line. So horizontal wear on the gauge face adds almost directly to measured gage, provided the rail hasn't rolled or moved on its plates.
| Item | Value |
|---|---|
| Track | Class 4 curve, rail laid to 56½ in. |
| High rail side wear at the gage line | 7/16 in. (0.44 in.) |
| Low rail side wear at the gage line | 1/16 in. (0.06 in.) |
| Static gage from wear alone | 56.50 + 0.44 + 0.06 = 57.00 in. |
| 213.53 maximum for Class 4 | 57.50 in. |
| Margin left for tie plate cutting, spike or fastener movement and dynamic widening | 0.50 in. |
The rail is not "defective" under Part 213 at any wear level. But in this example wear has already used half of the 1 in. allowance, so half an inch of widening from tired ties or fasteners puts the curve at the Class 4 limit. That's why track engineers read gage and side wear together on curves.
How does gage restraint testing (213.110) relate to wear?
Section 213.110 lets a track owner use a Gage Restraint Measurement System (GRMS), backed by a Portable Track Loading Fixture (PTLF), to show compliance with the crosstie and fastener rules in 213.109 and 213.127. It measures how much the gage opens under load; it does not measure rail wear.
The GRMS vehicle applies a vertical load of at least 10 kips per rail and measures gage at intervals of 16 in. or less. The rule defines unloaded gage (UTG), loaded gage (LTG), projected loaded gage at a 24-kip lateral and 33-kip vertical load (PLG24), and a gage widening projection (GWP). It sets two exception levels:
| Exception level | Limits in 213.110 | Required action (summary) |
|---|---|---|
| First level | UTG 58 in.; LTG 58 in.; PLG24 59 in.; GWP 1 in. | Protect with a 10 mph restriction, verify, restore lateral restraint |
| Second level | LTG 57¾ in. on Class 4 and 5 track; PLG24 58 in.; GWP 0.75 in. | Limit speed to the Class 3 maximum, verify |
The rule raises the second-level LTG limit by ¼ in. on Class 2 and 3 track, capped at 58 in. The owner must notify the FRA regional office at least 30 days before designating a line segment, and GRMS segments are tested at intervals of no more than 14 months (or 24 months on lines carrying 2 MGT or less with passenger speeds of 30 mph or less). Source: 49 CFR 213.110 on eCFR.
Side wear matters here because the GRMS starts from the unloaded gage. Every 1/16 in. of side wear at the gage line raises the UTG the system sees, leaving less room before the loaded gage reaches an exception. Wear and weak restraint add together.
Where do gauge face wear limits come from?
Rail wear limits, including side wear limits, come from each railroad's or transit agency's maintenance-of-way standards, which typically draw on AREMA recommended practice and on research into rail strength and wheel climb. None of them is federal law.
- AREMA. AREMA publishes recommended practices in the Manual for Railway Engineering (MRE), "published as a guide to railways in establishing their individual policies". AREMA's Committee 4 (Rail) lists "rail testing, rail wear, grinding and friction modification" in its scope and has a subcommittee on railwear, grinding and lubrication. The public 2023 table of contents for MRE Chapter 2 (Track Measuring Systems) lists a recommended practice for measuring rail wear parameters. The MRE is paywalled, so check the edition your contract or standard names; we don't reproduce its content here. See our guide to AREMA standards.
- Railroad standards. Wear limits are usually set by rail weight, curve, track class and traffic, often as combinations of side wear, head height loss and total head area lost. The values vary by owner, so use the table in the governing standard, never a figure from the internet.
- Research. FRA-sponsored work at the Volpe Center (DOT/FRA/ORD-98/07, December 1998) estimated allowable wear limits for vertical head loss and gauge face side wear from two failure modes, plastic bending and fracture. It found the fracture-based limits "more restrictive (i.e., conservative)" and recommended basing wear limits on fracture strength.
A 2014 University of Delaware study for the TRB Safety IDEA program (funded by FRA) reported that "most freight systems in North America have not adopted gauge face wear standards", meaning gauge face angle limits, while several US passenger and transit properties had (see the wheel-climb section below).
Key takeaway: if a bid or inspection report quotes a wear limit, it should name the railroad standard and edition it came from.
How is gauge face wear measured?
Side wear is measured against the new-rail profile for the same rail section, at a fixed reference point, so that repeat readings can be trended. The method should match the decision the reading supports.
| Method | What it gives | Typical use | Limits |
|---|---|---|---|
| Visual inspection | Contact band position, lipping, flow, gauge corner damage | Screening during track inspection | No numbers |
| Rail wear gauge or caliper | Side wear and head height loss at set points | Routine field readings on curves and switches | Depends on seating the gauge on an unworn reference |
| Gauge face angle gauge | Whether the worn face is steeper or flatter than a set angle | Switch points and high rails where wheel climb is a concern | Go/no-go, not a profile |
| Rail profile measurement (laser or contact) | The full head profile overlaid on the design profile | Grinding planning, wear rate and head area loss | Needs the correct reference profile and alignment |
| Track geometry car with rail profile system | Repeated profiles over long distances | Network trending | Needs field verification of exceptions |
A good measurement routine looks like this:
- Identify the rail section (for example 115RE or 136RE) and its design profile, because wear is measured against the new shape.
- Read side wear at the gage line, 5/8 in. below the top of rail, unless your standard names another point.
- Read head height loss at the head centerline in the same location.
- Record the gauge face angle where the standard calls for it, especially on switch points and stock rails.
- Measure track gage at the same spot so wear and gage can be compared.
- Mark the location by milepost, curve number and rail (high or low) so the next reading is in the same place.
- Trend the readings. A rail losing 1/32 in. a year and a rail losing 1/8 in. a year need different plans, even at the same reading today.
Related reading on profile shapes: rail profile types and ultrasonic inspection.
Why does the gauge face angle matter for wheel climb?
A worn gauge face can develop a flatter angle than the wheel flange was designed to ride against, and the flatter that angle, the lower the lateral-to-vertical force ratio (L/V) needed for a flange to climb the rail. The angle is measured between the worn gauge face and the vertical.
The classic Nadal criterion gives the L/V ratio at which flange climb begins:
L/V = (tan δ − μ) ÷ (1 + μ · tan δ)
where δ is the flange contact angle measured from horizontal (here δ = 90° − gauge face angle) and μ is the coefficient of friction at the flange.
Worked example: a 28° gauge face angle, lubricated and dry
| Gauge face angle (from vertical) | δ | μ = 0.2 (well lubricated) | μ = 0.4 (light to moderate) | μ = 0.5 (dry) |
|---|---|---|---|---|
| 18° | 72° | 1.78 | 1.20 | 1.02 |
| 24° | 66° | 1.41 | 0.97 | 0.82 |
| 28° | 62° | 1.22 | 0.85 | 0.71 |
| 32° | 58° | 1.06 | 0.73 | 0.61 |
Values are calculated from the Nadal formula above. At 28°, tan 62° = 1.881. With μ = 0.5: (1.881 − 0.5) ÷ (1 + 0.5 × 1.881) = 1.381 ÷ 1.940 = 0.71. With μ = 0.2 the same rail needs an L/V of about 1.22 to climb.
These match the University of Delaware study for TRB (Safety IDEA Project S-23, Zarembski, April 2014). The study notes that an L/V of 0.70 is "below the traditional Nadal wheel climb threshold of 0.8" and is measured in service regularly. Two lessons follow:
- Friction matters as much as angle. The same worn rail can be low-risk when lubricated and high-risk when dry.
- Angle limits are owner limits. The study reported US properties including Amtrak, BART, PAT and SEPTA using gauge face wear angle maintenance limits between 26° and 32°, and British Rail using 26°. Treat these as reported examples, not limits to adopt. The study developed a hand gauge with a 32° gauge face angle for checking switch points.
The study also identified excessively worn switch point and stock rail gauge faces as one of the conditions behind switch-point wheel climb. That links directly to 213.135(h) and to our guide to railroad switch and crossing inspection.
Why does rail head wear matter to ultrasonic rail testing?
Ultrasonic rail flaw testing assumes a rail head shape close to the design profile; a worn head changes where the probes sit, which parts of the head the beams reach and how the signals should be read. That is why head wear belongs in a rail testing plan, not only a track maintenance plan.
NTSB made the link after the October 20, 2006 New Brighton, Pennsylvania derailment (report NTSB/RAR-08/02), which NTSB linked to a rail defect that internal testing had not detected. One of its three recommendations to FRA was:
"Require that railroads use methods that accurately measure railhead wear to ensure that deformation of the head does not affect the accuracy of the measurements." (NTSB Safety Recommendation R-08-11)
A companion recommendation, R-08-10, asked that rail defect detection programs take into account factors including rail surface conditions and railhead wear. In its 2016 brief on the Lynchburg, Virginia derailment (NTSB/RAB-16/01), NTSB listed R-08-11 as "Closed—Acceptable Alternate Action". The same brief said fatigue in the lower corner of the gage face is hard to detect because that part of the head is not easily scanned by ultrasonic equipment. It also recorded that FRA's Rail Safety Advisory Committee formed a Rail Failure Working Group in September 2012 to study railhead wear, rolling contact fatigue and their effect on ultrasonic testing.
The table below gives the usual effects. Exact behavior depends on the test system and probe set, so treat it as typical practice to confirm with your Level III.
| Head condition | Effect on the ultrasonic search | What to do |
|---|---|---|
| Heavy side wear | The head is narrower and the gauge corner has moved, so probes centered on a nominal head can be off-center and gauge-side beams may miss the area they were set for | Adjust probe alignment for worn rail; record heavily side-worn curves in the test plan |
| Head height loss | Shorter sound paths to the head-web area; gates and depth readings set for new rail can be wrong | Use calibration and gating that suit the worn section |
| Flattened, wide or offset contact band | Probe coupling changes across the head; coupling loss can make a stretch invalid | Watch coupling indicators; treat poor-coupling stretches as untested under 213.237(g) |
| Lipping, metal flow, shelling or head checks | Surface damage can mask internal defects and scatter the beam | Plan hand verification; see rolling contact fatigue |
| Fatigue at the lower gauge corner | Hard to reach with standard probe angles (NTSB, 2016) | Consider added side-looking coverage or hand testing on high rails |
Where the search can't be completed because of rail condition, 49 CFR 213.237 treats the stretch as not inspected. The owner must then re-search it, reduce speed to 25 mph or replace the rail before the test deadline.
Key takeaway: worn rail is harder to test well, so the wear survey and the flaw test should share locations and information.
What happens when gauge face wear reaches a limit?
When side wear reaches the owner's limit, the usual responses are friction management, profile grinding, rail transposition or replacement, chosen by the governing standard and the rail's remaining life.
| Response | When it fits | Watch for |
|---|---|---|
| Gauge face lubrication or friction management | Wear rate is the problem, not current wear | Lubricant migrating to the top of rail; dry spots |
| Profile grinding | The profile has drifted, or surface damage is starting | Grinding removes head metal and can't restore side-worn metal; see rail grinding and ultrasonic testing |
| Transposing rail (moving the high rail to a low position) | Side wear is high but head height and rail condition are acceptable | Internal test the rail before and after relaying |
| Replacement | Wear has reached the limit, or the rail has defects | Plug rail used as a replacement must have been tested (213.237(c)) |
| Switch point repair or replacement | Worn or chipped points | Required under 213.135(h) |
Before any rail is moved or reused, it should be tested internally; our relay rail inspection guide covers why.
What gauge face wear measurement can't tell you
- It doesn't find internal defects. A rail can be within its wear limit and still carry a detail fracture or transverse defect. Only an internal test finds those.
- It doesn't predict climb on its own. Wheel climb depends on L/V, friction and wheel profile as well as the rail angle. A reading is one input.
- A single reading has no trend. Without earlier readings at the same spot, you can't tell a stable rail from one wearing quickly.
- Hand gauges need an unworn reference. On heavily lipped or flowed rail, the gauge may not seat correctly, and the reading drifts.
- Profile systems need the right reference profile. The wrong rail section gives the wrong wear values.
- Part 213 compliance isn't wear compliance. Passing 213.53 says nothing about whether the rail meets the owner's wear limit.
How EMA Industries applies this
EMA Industries performs ultrasonic rail flaw testing for transit agencies, short lines and industrial track owners, and is based in Southern California, mobilizing nationwide. On curves and turnouts with heavy side wear, the test plan should flag worn sections, note any stretch where coupling or rail condition prevented a valid search, and call for hand verification where needed. To plan testing on worn or curved track, see our ultrasonic rail testing services or contact us.
Related reading: AREMA standards · 49 CFR 213.237 rail flaw detection requirements · Rail profile types and ultrasonic inspection · Rail grinding and ultrasonic testing · FRA track safety standards
Frequently asked questions
Is there an FRA limit for gauge face wear?
No. 49 CFR Part 213 sets no rail head wear or side wear limit for running rail. It limits track gage under 213.53, and the wear limits come from the track owner's standards, usually informed by AREMA practice.
Where is gauge face wear measured?
Usually at the gage line, 5/8 in. below the top of rail, which is the same plane FRA uses to measure track gage in 213.53(a). Your railroad's standard may name a different point, so follow it.
What is the maximum track gage on Class 4 and 5 track?
4 ft 9½ in. (57½ in.), with a minimum of 4 ft 8 in., under 49 CFR 213.53. Class 2 and 3 track allows up to 57¾ in., and Class 1 track up to 58 in.
What gauge face angle increases wheel climb risk?
There is no single federal number. Under the Nadal formula, a 28° gauge face angle with dry rail (μ = 0.5) lets a flange climb at an L/V of about 0.71. Several US transit and passenger properties have been reported using maintenance limits between 26° and 32°.
Can worn rail be tested ultrasonically?
Yes, but worn heads change probe contact and beam coverage, so the test system must be set up for the worn section. Any stretch where a valid search couldn't be made counts as untested under 213.237(g).
Sources
- 49 CFR 213.53, Gage, eCFR (read on Cornell LII, October 2026)
- 49 CFR 213.110, Gage restraint measurement systems, eCFR (read on Cornell LII)
- 49 CFR 213.323, Track gage (Class 6 and higher), eCFR
- 49 CFR 213.135, Switches and 213.137, Frogs, eCFR
- 49 CFR 213.237, Inspection of rail, eCFR
- 49 CFR Part 213, annual CFR XML (revised as of October 1, 2024), govinfo, used for the full-text search
- NTSB/RAB-16/01, CSXT crude oil train derailment, Lynchburg, Virginia (April 30, 2014), NTSB, includes the text and status of R-08-9, R-08-10 and R-08-11
- Track Safety Standards; Improving Rail Integrity, proposed rule (October 19, 2012), Federal Register via govinfo
- Estimation of Rail Wear Limits Based on Rail Strength Investigations, DOT/FRA/ORD-98/07, Volpe Center for FRA, December 1998
- Reducing Wheel Climb at Switch Points to Reduce Derailments, Safety IDEA Project S-23, A. M. Zarembski, University of Delaware, TRB, April 2014
- AREMA Committee 4, Rail, arema.org
- AREMA MRE 2023 Chapter 2 table of contents, publications.arema.org