49 CFR 213.237 is the FRA rule that requires track owners to test rail internally for hidden flaws. On Class 4 and 5 track, and on Class 3 track that carries scheduled passenger trains or is a hazardous materials route, internal rail inspections can be no more than 370 days or 30 million gross tons (MGT) apart, whichever comes first. The rule also caps how often rail can break in service, defines what counts as a valid search, and says what must happen when part of the rail was not properly tested.
Internal testing is required in addition to the visual track inspections in 49 CFR 213.233. A track inspector walking or riding the line can't see a transverse fissure growing inside the rail head. An ultrasonic search can.
This guide covers each part of 49 CFR 213.237 and the rules that sit beside it: operator qualification (213.238), records (213.241) and remedial action (213.113). It ends with how to plan a testing program and what to put in a rail flaw detection RFP.
How often must rail be internally tested under 49 CFR 213.237?
The interval depends on track class and traffic. Section 213.237(c) sets two schedules:
| Track | Maximum interval between internal rail inspections |
|---|---|
| Class 4 and 5 | 370 days or 30 MGT, whichever is shorter |
| Class 3 with regularly scheduled passenger trains, or a hazardous materials route | 370 days or 30 MGT, whichever is shorter |
| All other Class 3 track | Once each calendar year (no more than 18 months apart) or once every 30 MGT, whichever is longer, and never more than 5 years apart |
Source: 49 CFR 213.237(c) on eCFR. Class 6 and higher track falls under Subpart G instead (49 CFR 213.339).
Under 213.237(j), a hazardous materials route is track carrying at least 10,000 car loads or intermodal portable tank loads of hazardous materials in a calendar year, or at least 4,000 loads of the specific materials listed in 49 CFR 172.820.
Worked example: when the tonnage limit comes first
Days and tonnage both run from the last test, and on the shorter schedule whichever limit is reached first sets the deadline.
| Segment | Annual traffic | 30 MGT reached after | Test due |
|---|---|---|---|
| Class 4 freight main line | 40 MGT | about 9 months (≈274 days) | at about 274 days, tonnage controls |
| Class 4 secondary line | 12 MGT | 2.5 years | at 370 days, calendar controls |
| Class 3 line, no passenger trains, not a hazmat route | 5 MGT | 6 years | within 5 years: the "whichever is longer" rule would allow 6 years, but the 5-year cap applies |
The third row is the one most often misread. For "other" Class 3 track the rule takes the longer interval, so a lightly used line may legally go several years between tests. The legal minimum isn't necessarily the right interval for your risk, especially on older rail or where service failures have occurred.
What is a rail inspection segment?
The interval and the service failure rate are both measured per rail inspection segment, a stretch of track with defined milepost limits that the owner designated under 213.237(b). Owners had to designate segments by March 25, 2014. To create or change one, the owner submits a detailed request to FRA's Associate Administrator for Railroad Safety. FRA reviews it within 30 days, and the existing designation stays in force until a new one is approved.
Why the rule looks the way it does: the 2014 rail integrity rule
Most of today's 213.237 comes from FRA's final rule Track Safety Standards; Improving Rail Integrity, published January 24, 2014 and effective March 25, 2014. It carried out section 403 of the Rail Safety Improvement Act of 2008. The rule:
- moved internal rail testing to a performance-based standard measured by service failure rates per segment
- defined the valid search
- created the qualified operator requirements in 213.238
- added the plug rail testing requirement
- revised the remedial action table for transverse defects and other defect types in 213.113
- gave owners a four-hour window to verify certain suspected defects
That history explains why the rule is about outcomes and evidence, not just a test date.
What counts as a "valid search"?
A test vehicle passing over the rail doesn't, on its own, satisfy the rule. Section 213.237(j) defines a valid search as:
"a continuous inspection for internal rail defects where the equipment performs as intended and equipment responses are interpreted by a qualified operator."
Two conditions must both hold: the equipment worked, and a qualified operator read the results. Under 213.237(g), if the operator decides a valid search could not be made over a stretch of track, that stretch does not count as inspected. Common causes are lost coupling, heavy surface damage, contamination and equipment faults.
What happens when part of the rail can't be searched?
Section 213.237(h) gives the track owner three options, and one must be completed before the time or tonnage limit expires:
- Conduct a valid search over the affected rail.
- Reduce operating speed to no more than 25 mph until a valid search can be made.
- Replace the rail that was not inspected.
The rule has no fourth option. A failed search close to the end of the window is a scheduling emergency, not a paperwork issue. That's why experienced owners schedule tests well before the deadline, leaving time for a re-test.
How ultrasonic testing finds the defects 213.237 targets
Section 213.237 counts four defects as service failures: transverse fissures, detail fractures, compound fissures and vertical split heads. Each lies in a different orientation inside the rail head, so a test system uses several beam angles at once. A typical configuration looks like this, though exact probe sets vary by system and manufacturer:
| Defect | Orientation in the rail head | Typical ultrasonic approach |
|---|---|---|
| Transverse fissure | Crosswise, starting from an internal nucleus | 70° shear-wave probes looking forward and backward |
| Detail fracture | Crosswise, starting from surface shelling or head checks | 70° shear wave; surface damage can mask it, so a valid-search check matters |
| Compound fissure | Starts as a horizontal split, then turns crosswise | 70° shear wave for the transverse part, 0° for the horizontal part |
| Vertical split head | Lengthwise, in a vertical plane through the head | 0° (loss of back-wall echo) plus angled side-looking probes |
This is why 213.237(e) requires defects to be marked and 213.113 sets what happens next. Finding the flaw is only the first step. The defect types and their remedial actions are covered in our guide to FRA defect codes.
What is the rail service failure rate, and what if it's exceeded?
A service failure is a broken rail caused by one of those four internal defects (213.237(j)). Track owners must keep the rate of these failures within limits for each designated rail inspection segment:
| Track | Maximum service failures per year per mile |
|---|---|
| Class 4 and 5 | 0.10 |
| Class 3, 4 and 5 with scheduled passenger trains or a hazmat route | 0.09 |
| Class 3, 4 and 5 with scheduled passenger trains and a hazmat route | 0.08 |
The rate is calculated over a 12-month period and must be worked out within 45 days after the period ends (213.237(a)). Failures in rail later replaced through relay aren't counted, but rail used to repair a service failure isn't treated as relay rail.
Worked example. A 20-mile Class 4 segment has 3 service failures in 12 months: 3 ÷ 20 = 0.15 per mile per year, which is over the 0.10 limit.
If a target is missed:
- Notify FRA within 45 days after the period ends. The owner may explain why the target was missed and submit a remedial action plan (213.237(d)).
- After two consecutive years missed, the owner must either cut the test interval to 10 MGT or reduce the track to Class 2 in the area with the most service failures, until the target is met.
- Short segments have an exception. If a single failure would by itself push the rate over the limit (for example, one failure on a 5-mile segment), the segment is treated as compliant unless a second failure occurs in the same 12-month period.
Who can operate rail flaw detection equipment?
Section 213.237(i) requires the operator to be a qualified operator under 49 CFR 213.238 with demonstrated proficiency on each type of equipment assigned. Section 213.238 sets out what that means:
- A documented training program. Each provider of rail flaw detection must have one, and must identify the equipment types each operator is trained and qualified on. A track owner may not use a provider that doesn't comply.
- Written authorization from the employer to do four things: conduct a valid search, determine that the equipment is performing as intended, interpret responses and act on them under the employer's procedures, and confirm that each search was continuous and not compromised by contamination, rail conditions or equipment malfunction.
- At least 160 hours of rail flaw detection experience under the direct supervision of a qualified operator or a manufacturer's representative, plus demonstrated proficiency before initial qualification and before authorization on each equipment type.
- Reevaluation and recurrent training. The employer sets the schedule in its documented program. Reevaluation needs a recorded examination and demonstrated proficiency on each equipment type. The rule sets no fixed refresher interval.
- Records. For each qualification: the employee's name, the equipment covered, the date of qualification and the date of the most recent reevaluation, kept where FRA can inspect them.
In an RFP, ask for the operator's 213.238 qualification record for the specific equipment that will be used, not just a general NDT certificate. The equipment itself must be able to find defects between joint bars, in the area the bars cover (213.237(f)).
How must defective rail be marked?
Every defective rail must carry a highly visible marking on both sides of the web and base. Where permanent features make those surfaces inaccessible, the marking may go on or next to the rail head (213.237(e)). What must then be done about the defect (speed restriction, protection or replacement) is set by the remedial action table in 49 CFR 213.113, not by 213.237.
What records must a 213.237 inspection produce?
49 CFR 213.241 sets the record for each internal rail inspection. It must state:
| Record item | Notes |
|---|---|
| Inspection date | |
| Track inspected, with beginning and end points | Matches the designated segment |
| Location and type of each defect found | Classified under 213.113 |
| Size of each defect | Required if it wasn't removed before the next train movement |
| Initial remedial action and its date | |
| Location of any track not validly tested | The 213.237(g) stretches |
Records must be kept for at least two years after the inspection and one year after the initial remedial action. Owners must also keep records showing how they computed each segment's service failure rate. Electronic records are allowed if the system:
- uniquely identifies each author
- prevents completed records from being changed or replaced
- stores amendments separately, each identified by its author
- starts storing the record within 72 hours of the inspection
Practical point: if your testing contractor's report doesn't list the untested stretches and each defect's size and location, you can't build a compliant record from it.
Does plug rail need testing?
Yes. Plug rail is rail removed from one location and stored for use as replacement rail elsewhere. Under 213.237(c):
- Replacement plug rail must have been tested for internal flaws.
- For plug rail installed after March 25, 2014, the rail must not have accumulated more than 30 MGT across its old and new locations since its last test.
- If non-compliant plug rail is in track, trains must run at Class 2 speeds or below until it is tested.
Relay and plug rail are covered in more depth in our guide to relay rail inspection.
How to plan an annual 213.237 testing program
- List every segment with its class, passenger and hazmat status, and milepost limits.
- Get tonnage data for each segment so you can project when 30 MGT will be reached.
- Set each test date from the earlier of the two limits, then pull it forward by several weeks to leave room for a re-test after any invalid search.
- Choose the method for each segment. A test vehicle suits long mainline runs, while hand or cart testing suits yards, special trackwork, bridges, tunnels and short segments. Compare the options in our guide to hi-rail, cart and walking tests.
- Confirm operator qualification under 213.238 for the exact equipment.
- Agree the defect hand-off. Decide who marks, who notifies, and how fast 213.113 remedial action starts.
- Track the service failure rate monthly, not just at the 12-month calculation, so a rising trend is caught early.
- File records to the 213.241 standard and keep them for at least two years.
What to include in a rail flaw detection RFP
Transit agencies and short lines that contract out testing usually get better proposals when the RFP states:
- Scope: track miles by class and segment, special trackwork, and any freight or passenger overlap
- Method: test vehicle, hand or cart testing, or both, and the minimum probe configuration
- Compliance: 213.237 intervals, 213.238 operator qualification records, 213.241-compliant reporting, and continuous testing under 213.240 if offered
- Reporting: defect location, type and size, untested stretches, report format and turnaround time
- Defect handling: marking, immediate notification and verification of suspect locations
- Safety: roadway worker protection under 49 CFR Part 214, and for transit, the agency's own safety rules
- Credentials: references from comparable track, insurance and any agency vendor registration
Common 49 CFR 213.237 compliance mistakes
| Mistake | Why it's a problem |
|---|---|
| Counting a test run as a completed inspection | Only a valid search counts; untested stretches need retest, a 25 mph limit or replacement |
| Tracking days but not tonnage | Busy lines hit 30 MGT well before 370 days |
| Misreading the "other Class 3" rule | It's "whichever is longer" with a 5-year cap, the opposite of the rule for higher classes |
| Installing untested plug rail | Trains are limited to Class 2 speeds until it's tested |
| Calculating the failure rate late | It's due within 45 days after each 12-month period |
| Confusing 213.237 with 213.113 | 213.237 sets when and how to test; 213.113 sets what to do about a defect |
| Accepting a report without untested stretches listed | 213.241 requires them, and you can't show compliance without them |
What 49 CFR 213.237 does not cover
| Topic | Where it lives |
|---|---|
| Visual track inspection frequency | 213.233 |
| Continuous rail testing (optional alternative with field verification) | 213.240 |
| What to do about a defect once found | 213.113 |
| Class 6 and higher track | 213.339 |
| Rail transit systems | Also subject to state safety oversight; in California, the CPUC |
A compliant interval also doesn't guarantee that every flaw was found. Shelling, head checks and surface damage can mask internal defects from ultrasonic beams. That's why the rule pairs the schedule with the valid-search definition and a service failure rate that measures real outcomes.
A 213.237 compliance checklist
- Track class and operating conditions (passenger, hazmat route) confirmed for each segment
- Rail inspection segments and milepost limits on file
- Days and MGT since the last test tracked for every segment
- Equipment capable of searching between joint bars
- Operator qualified under 213.238 for the specific equipment used
- Every stretch without a valid search recorded and resolved before the limit expires
- Defective rail marked on both sides of web and base
- Plug rail test status verified before installation
- Records meet 213.241 and are kept at least two years
- 12-month service failure rate calculated within 45 days
- FRA notified within 45 days if a target is missed
How EMA Industries applies this
EMA Industries performs ultrasonic rail flaw testing for transit agencies, short lines and industrial track owners. We're based in Southern California and mobilise nationwide. Whoever does your testing, the report should record the segment, the mileposts, any stretch where a valid search couldn't be made, and the location, type and size of each defect. Without that, the owner can't show compliance with 213.237 and 213.241. To scope an annual testing program or an RFP, see our ultrasonic rail testing services or request a quote.
Related reading: How often must rail be tested? · How ultrasonic testing works for railways · FRA defect codes explained · FRA track safety standards (Part 213)
Frequently asked questions
How often are train tracks tested for internal flaws?
On Class 4 and 5 track, and on Class 3 track with scheduled passenger trains or a hazmat route, at least every 370 days or 30 MGT, whichever comes first. Other Class 3 track follows an annual or 30 MGT schedule, whichever is longer, with a 5-year maximum.
What happens if a rail flaw test misses part of the track?
That stretch doesn't count as inspected. Before the deadline, the owner must retest it, cut speed to 25 mph, or replace the untested rail.
Who is allowed to operate rail flaw detection equipment?
Only an operator qualified under 49 CFR 213.238. That means documented training, at least 160 supervised hours, written employer authorization and demonstrated proficiency on that specific equipment.
How long must rail flaw inspection records be kept?
At least two years after the inspection and one year after the initial remedial action, under 49 CFR 213.241.
What is a rail service failure?
A broken rail caused by a compound fissure, transverse fissure, detail fracture or vertical split head. Class 4 and 5 track may have no more than 0.10 per mile per year.
Does 213.237 apply to Class 1 and 2 track?
No. The internal testing requirement covers Class 3, 4 and 5 track, and Class 6 and higher falls under 213.339. Owners of lower-class track may still choose to test.
Sources
- 49 CFR 213.237, Inspection of rail, eCFR, current as of October 2026
- 49 CFR 213.233, Track inspections, eCFR
- 49 CFR 213.238, Qualified operator, eCFR
- 49 CFR 213.240, Continuous rail testing, eCFR
- 49 CFR 213.241, Inspection records, eCFR
- 49 CFR 213.113, Defective rails, eCFR
- 49 CFR 213.339, Inspection of rail in service (Class 6 and higher), eCFR
- Track Safety Standards; Improving Rail Integrity (January 24, 2014), Federal Register
- Cornell LII text of 49 CFR 213.237 (alternate copy)