Reference

Trenchless vs. Open Cut: When Each Is Required

A crossing goes trenchless when a regulation, a property owner, or a physical risk makes open cut unavailable - not when it happens to be cheaper. Fourteen conditions account for nearly every forced trenchless call on a utility alignment.

The default is open cut

Worth stating plainly, because rule sets tend to drift conservative over time: open cut with standard bedding and backfill is the default method, and most crossings on most alignments are open cut. Trenchless is what you do when something forbids it.

A rule set that calls trenchless on every water feature is wrong, not merely cautious. It inflates the estimate, and it trains the people reading the schedule to stop believing it.

Roads and rail

Rule	Condition	Casing	Basis
R1	Any TxDOT-owned roadway, regardless of functional classification	Yes	TxDOT Utility Accommodation Rules, 43 TAC 21.37 - open cut prohibited within TxDOT ROW regardless of road class.
R1B	On-system state roadway - the source data's own on/off-system flag says the state DOT maintains it	Yes	Same rule, applied on the DOT's own on-system determination (TxDOT's SYSTEM column) where no owner is attributed.
R2	Highway or freeway-class road where ownership is not attributed in the source data	Yes	Same rule, applied as a classification-based fallback. Confirm actual ownership.
R3	Railroad track crossing	Yes	AREMA Ch. 1 Pt. 5 - cased bore required under the track structure.
R9	Municipal arterial or principal collector (non-TxDOT)	Yes	Municipal ROW ordinance - pavement cut restrictions by roadway classification.
R11	Railroad-owned parcel - carrier real estate, not just the track centerline	Yes	AREMA Ch. 1 Pt. 5 and carrier permitting requirements. Carriers also press for a near-perpendicular crossing angle to limit bore length and track disturbance.

R1 is the one that surprises people

It applies regardless of road class. A two-lane farm-to-market road under TxDOT ownership is as much a forced bore as an interstate. This is why a route study whose data does not carry road ownership - as distinct from road classification - systematically underestimates cost.

R11 is the one that gets missed

Rail carriers own real estate well beyond the track itself. Testing only the track centerline misses crossings of carrier-owned parcels, which permit the same way, take the same time, and cost the same money.

Water

Rule	Condition	Casing	Basis
R5	Perennial stream or river	No	USACE Section 404, Nationwide Permit 58 - utility lines for water and other substances. NWP 12 has covered oil and gas only since the 2021 split; NWP 57 covers electric and telecom. Trenchless preferred to avoid in-channel disturbance on a perennial waterway.
R6	River, pond, lake or reservoir - major or standing water	No	Same basis, applied as a class-based fallback where the source data does not populate a flow-regime flag.

What is deliberately not on this list

Wetlands, marshes, canals, and intermittent or unattributed streams do not force trenchless. Open cut with proper restoration is accepted practice for those. A rule mandating trenchless for every hydro feature would roughly double the trenchless footage on a typical alignment for no regulatory reason.

A data trap worth knowing. The National Hydrography Dataset states flow regime as an integer FCode - 46006 means perennial - not as text. Any rule that tests for the string “perennial” silently classifies every genuine perennial stream as open cut. On one real Fort Worth corridor, that single error affected 231 stream crossings.

Existing utilities

Rule	Condition	Casing	Basis
R7	Existing main 24 in diameter or larger	No	Open cut adjacent to a large transmission main risks undermining it; a bore maintains the existing bedding.
R8	Pressurized gas or petroleum line, 18 in or larger	No	Engineering judgement, not a regulation: open cut across a large live pressurized line risks loss of support and pipe failure, and leaves too little room to establish clearance. The engineer of record makes the final call.
R8B	Pressurized gas or petroleum line of unrecorded diameter	No	The source data records no diameter, so the 18 in test cannot be applied. Treated as large until the line is located and its size confirmed. The engineer of record makes the final call.
R4	Oncor-owned electric transmission or distribution	Yes	Oncor joint-use and franchise crossing requirements plus NESC clearances - open cut beneath or adjacent to transmission structure foundations is not permitted.

Size is what decides a live pressurized line, not the product in it. Open cut under a small line is routine work; the failure modes that make it a bore - losing support under the pipe, and having no room left to establish clearance - are what large diameter brings. Roughly nine in ten pipelines in the Texas Railroad Commission layer are under 18 in, so this distinction is most of the trenchless footage on a real alignment.

Rule	Condition	Casing	Basis
R8C	Pressurized gas or petroleum line under 18 in	n/a	Open cut is acceptable on a pressurized line under 18 in at 4 ft of cover or less. Depth of cover is not carried in the source data and is not checked - confirm it on location before relying on this. The engineer of record makes the final call.

What the tool does not know, and says so. The threshold has a second half - cover of 4 ft or less - and no pipeline dataset published in Texas carries a depth field, so it cannot be tested. R8C therefore states the assumption in the crossing schedule rather than hiding it, and every rule in this family ends the same way: the engineer of record makes the final call. These are recommendations on a drawing, not determinations.

Federal land and flood-control works

Rule	Condition	Casing	Basis
R10	USACE fee-owned land or flowage easement	Yes	USACE real estate requirements and Section 408 review - open cut across Corps-owned fee land requires a real estate outgrant and is avoided by policy.
R12	Levee, floodwall or dam embankment	Yes	33 U.S.C. 408 permission is required to alter a federal flood-control work, and USACE EM 1110-2-1913 governs how - a conduit through an embankment is bored and cased with seepage control. Open cut of the embankment section is a breach, not a method.

Why a levee is not just another utility. The instinct with a buried line is that paralleling it is fine and crossing it is the event. An embankment inverts that. Utilities cross levees constantly, and USACE permits a bored, cased crossing with seepage control as ordinary business. What does not get permitted is a conduit run lengthwise through or beside the embankment: its own backfill becomes a preferential seepage path, which is the internal-erosion mechanism levee design exists to prevent.

How the rules resolve

First match wins, and the order matters. A perennial stream inside a TxDOT right-of-way is an R1 crossing, not R5 - the casing requirement is the binding one. Anything matching no rule is open cut.

Each crossing should carry the rule ID that decided it, not just the resulting method. “Bore, because R1” is something a permitting engineer can review and disagree with. “Bore” is not.

Scope, and what this does not do

This rule set is Texas-specific where it touches state agencies - R1, R2 and R9 cite TxDOT and Texas municipal practice. The federal bases (AREMA, NWP 58, Section 408, NESC) apply nationally. Outside Texas the roadway rules need a local equivalent substituted.

It is also a screening rule set. It tells you a bore is required and roughly what it will cost. It does not size the bore, select between auger boring, HDD and microtunneling, or evaluate whether the geology at that station supports any of them.