Interview guides · HNTB

HNTB Software Engineer Interview Guide

HNTB Software Engineer interview guide: reported rounds, questions and how candidates describe the process.

The 60-second brief

As a Software Engineer at HNTB, you play a vital role in advancing the digital landscape of one of the nation’s premier employee-owned infrastructure firms. Rather than building traditional consumer tech applications, software engineers at HNTB build, integrate, and modernize technology solutions that directly support massive civil, transportation, bridge, and architectural projects across North America. Your work bridges the gap between software development and complex engineering workflows, empowering project managers, client entities, and specialized engineering teams to deliver critical infrastructure safely and efficiently. In this role, you will work on custom web applications, enterprise databases, internal workflow automation systems, specialized CAD/CADD tool integrations, and spatial data visualization platforms.

This guide is scoped to a Software Engineer candidate at HNTB.

Focus areas

Interview preparation (resume & background)
Behavioral interviewing / storytelling
Project-based technical discussion

The HNTB interview process

HNTB candidates report 4 rounds over 3-5 weeks. The stages below are what candidates describe, not a published process.

Initial Conversation

Candidates begin with a conversation with an internal recruiter or campus talent acquisition representative.

What to demonstrate

Candidates begin with a conversation with an internal recruiter or campus talent acquisition representative
Depth in Interview preparation (resume & background)

How to prepare

Answer aloud and timed: Walk me through a complex technical project on your resume, specifically detailing your personal contributions and architectural decisions.
Answer aloud and timed: Can you explain a scenario where you had to adapt your software design to meet unexpected user or client constraints?

Virtual Panel Interviews

Candidates participate in virtual panel interviews with local office department managers, project leads, and senior engineers.

What to demonstrate

Candidates participate in virtual panel interviews with local office department managers, project leads, and senior engineers
Depth in Interview preparation (resume & background)

How to prepare

Answer aloud and timed: What specific technologies or software frameworks did you leverage in your previous internships or roles, and how proficient do you consider yourself in each?
Answer aloud and timed: Describe a situation where you had to debug an issue in a project that was already deployed or close to a deadline.

Office Visit Invitation

In many regional offices, candidates receive an invitation to visit the office in person, meet team members, and take a workspace tour.

What to demonstrate

In many regional offices, candidates receive an invitation to visit the office in person, meet team members, and take a workspace tour
Depth in Interview preparation (resume & background)

How to prepare

Answer aloud and timed: How have you integrated specialized engineering tools, third-party APIs, or database scripts into past applications?
Answer aloud and timed: How do you structure a front-end web application (e.g., using JavaScript frameworks) to ensure responsive performance and maintainability?

Discussion with Leadership

Candidates discuss long-term team expectations with executive leadership or office directors.

What to demonstrate

Candidates discuss long-term team expectations with executive leadership or office directors
Depth in Interview preparation (resume & background)

How to prepare

Answer aloud and timed: Describe your experience with CADD software, spatial data, or domain-specific technical tools mentioned in your application materials.
Answer aloud and timed: How do you approach writing clean, testable code when working on a tight schedule or delivering against a fixed questionnaire assessment?

Where candidates lose points

Highlight Resume Specifics

Be ready to explain the precise mechanics, code structure, and individual contributions for every single project listed on your resume. Interviewers focus deeply on your real past experience.

Emphasize Career Longevity

HNTB takes pride in its low turnover and private employee-ownership model. Clearly state your desire to build a long-term career and grow with the company.

Prepare Practical Questions

Take advantage of the dedicated question time in every interview. Ask about local office initiatives, prospective project pipelines, and how the software team collaborates with civil engineering departments.

Practice Your 5-Year Narrative

Formulate a thoughtful response explaining where you want your engineering skills to evolve over the next five years and how HNTB fits into that progression.

Questions & practice

Track a rolling failure rate per destination for circuit decisions

Easy · sliding window · ring buffer · circuit breaker

The egress service delivers about 1,500 webhooks per second across roughly 40,000 destinations, each call bounded by a 10 second timeout. Maintain, per destination, the failure rate over the trailing 60 seconds so a caller can ask before dispatch whether the circuit should open. Attempts arrive as (destination_id, finished_at_ms, outcome). Requirement: amortised O(1) per attempt, with total memory bounded by the destination count rather than by traffic. Give the structure, its exact memory, and the rule that stops a destination with three attempts from opening a circuit.

Approach

Name the exact-deque version and then reject it as the default. Holding timestamps and advancing a tail pointer past anything older than now minus 60 seconds is a correct two-pointer window at amortised O(1) per attempt, but its memory tracks in-window traffic, so one destination in a retry storm holds hundreds of thousands of entries while thousands of quiet destinations hold none.
Use a ring of 60 one-second buckets per destination, each bucket a pair of counters for attempts and failures. On an attempt, advance the ring by the elapsed whole seconds, zeroing at most min(elapsed, 60) buckets, then increment the head. That is amortised O(1) with a fixed footprint per destination.
State the footprint: 60 buckets times two 4-byte counters is 480 bytes of payload per destination, so 40,000 destinations is roughly 20 to 25 MB with per-entry overhead, bounded by the catalogue rather than by the rate. The cost is granularity, since the oldest bucket ages out in whole seconds, which is far tighter than the decision needs.
Require a minimum sample before the circuit may open. A destination with three attempts and three failures reads as 100 percent and is not evidence; a floor of roughly 20 attempts in the window makes the ratio meaningful, and below that floor use a run of consecutive failures as the trigger instead.

Follow-up

The fleet is 30 instances and each sees roughly a thirtieth of a destination's traffic. Where does the rate actually live, and what does a per-instance answer get wrong?
A destination answers in 9.5 seconds and succeeds. It is not failing but it is consuming your per-destination concurrency. What signal should open the circuit here?

Merge partitioned event streams into one ordered feed with bounded lateness

Hard · k-way merge · watermarks · out-of-order streams

The read-model service consumes 64 log partitions carrying about 4,000 events per second in total. Each partition is ordered within itself, but partitions drift by up to 30 seconds, and the activity feed must present a tenant's events in occurred_at order. Produce the merge. State its complexity, the buffer it requires in events and in bytes, what happens when one partition is idle, and what you do with an event that arrives after you have already emitted its position. Payloads average 1 KB.

Approach

Merge with a min-heap over the 64 partition heads keyed on (occurred_at, event_id): O(log P) per event and O(n log P) overall. The tie-break on event_id is what makes the output deterministic when two partitions carry the same millisecond, which matters because the feed is paginated and a non-deterministic order reorders pages under the reader.
Emitting the heap head is only correct once every partition has produced everything up to that timestamp, so the emit condition is a watermark: the minimum across partitions of the highest occurred_at seen, less the allowed lateness. Events are held until the watermark passes them, which is what turns individually ordered streams into a jointly ordered one.
Size the buffer from the lateness rather than guessing: 4,000 events per second times 30 seconds is 120,000 buffered events, and at 1 KB each about 120 MB of heap. That number is the real price of the ordering guarantee and belongs in front of whoever asked for it.
Handle the idle partition explicitly, because it fails the feed rather than corrupting it: a partition with no traffic never advances its own maximum, so the watermark freezes and output stops entirely. Either every partition emits a periodic idle marker carrying the broker's current time, or the watermark falls back to wall clock for a partition silent beyond a threshold.

Follow-up

The lateness budget is raised to five minutes. What is the new buffer, and what besides memory changes?
The consumer restarts. Where does it resume from, and what does the feed look like for the first 30 seconds?

Collapse a redelivered event batch into per-aggregate high-water marks

Easy · hashing · at-least-once · aggregation

You drain a batch of up to 5,000,000 events, each (aggregate_id BIGINT, aggregate_version INT, event_type, payload). The log guarantees order within one aggregate only; the batch merges 64 partitions, and a relay failover has redelivered a range, so an older version for an aggregate can appear after a newer one. Given a map of last_applied_version per aggregate, produce the events worth applying, at most one per (aggregate_id, version), plus the count discarded. Target O(n) time. State the memory for 2,000,000 distinct aggregates and what you do when it does not fit.

Approach

One pass, one hash map from aggregate_id to the highest version kept, and a discard counter. An event whose version is at or below last_applied_version for its aggregate is dropped without further work, which is the whole reason the event carries its version rather than a delta. O(n) expected time, O(d) space in distinct aggregates.
Keep the maximum, never the last occurrence. The redelivered range means the final appearance of an aggregate in the batch can be an older version than one seen earlier in the same batch, so last-wins applies stale state over newer state and the projection regresses with no error anywhere.
Cost the memory instead of calling it large: an 8-byte key plus a 4-byte version is 12 bytes of payload, and an open-addressed table held at a 0.7 load factor costs roughly 17 bytes per entry before per-slot metadata, so 2,000,000 aggregates is tens of megabytes in a native layout and several times that in a runtime that boxes both key and value.
If the distinct set exceeds memory, partition on hash(aggregate_id) mod P and reduce each partition independently. Every event for one aggregate hashes to the same partition, so the per-partition result is exact and the merge is concatenation rather than a second reduction.

Follow-up

The payload is a patch rather than a snapshot, so applying only the highest version loses the intermediate changes. What changes in your reduction?
How do you detect that version 7 arrived while version 6 was never delivered, and what should the consumer do about the gap?

Explain why the owner filter ignores the listing index

Medium · composite index · query plans · sort elimination

The only index on resource is (tenant_id, status, updated_at DESC, resource_id DESC). A new endpoint returns one user's resources across all statuses, newest created first: WHERE tenant_id = $1 AND owner_user_id = $2 ORDER BY created_at DESC LIMIT 20. On a tenant with 2M rows it takes 900 ms and EXPLAIN shows a sort above a large scan. Explain precisely why the existing index cannot serve it, give the index that can, and state which of these the new index still will not help: owner_user_id alone across tenants; the same query ordered by updated_at. PostgreSQL 16.

Approach

Separate the two jobs an index does. For filtering, a composite btree is seekable only on a left prefix, so with no predicate on status the scan can at best range over tenant_id and test owner_user_id per row; PostgreSQL 16 has no btree skip scan to jump the unconstrained column.
For ordering, the index is sorted by (status, updated_at) within a tenant and not by created_at, so the LIMIT cannot stop early: every matching row is read and then sorted. That is the 'Sort Method: top-N heapsort' line, and it is why the plan reads 2M rows to answer with 20.
Derive the replacement from the access path — equality, equality, then the ordering column: CREATE INDEX CONCURRENTLY ON resource (tenant_id, owner_user_id, created_at DESC). The scan seeks to the (tenant, owner) range and walks 20 entries in order, so the Sort node disappears along with the row-read.
Treat INCLUDE (title, status) as conditional, not free. An index-only scan still visits the heap for any row whose page is not marked all-visible, so on a table taking 1.2k writes/second the win depends on autovacuum keeping the visibility map current, and the wider index costs more on every insert.

Follow-up

90% of rows are status='active'. Would a partial index WHERE status = 'active' change your answer, and for which of the three queries?
A dashboard runs this for 40 owners in one page load. What changes about the design?

Write the update path that detects a concurrent edit

Medium · optimistic concurrency · transactional outbox · audit history

resource carries version INT NOT NULL DEFAULT 1. resource_revision holds revision_id, resource_id, version, actor_user_id, change_kind, patch JSONB, request_id, created_at with UNIQUE (resource_id, version). outbox_event holds aggregate_type, aggregate_id, aggregate_version, event_type, payload, status. A PUT carries the version the client read. Write the exact statements for the single transaction that applies the edit, records the revision and enqueues 'resource.updated', and give the handler's branch on zero affected rows. Then say what PostgreSQL 16 does under READ COMMITTED when two of these updates hit one row at once.

Approach

One transaction, three writes, no network call inside it: UPDATE resource SET title = $3, version = version + 1, updated_at = now() WHERE resource_id = $1 AND tenant_id = $4 AND version = $2; then INSERT the resource_revision row at version $2 + 1; then INSERT the outbox_event row at the same aggregate_version. The event goes to a table rather than a broker because no transaction spans both.
Branch on the affected-row count before doing anything else. Zero has three causes — stale version, wrong tenant, row gone — so re-read once and map to 409 carrying the current version, or 404 for an id outside the caller's tenant, which also stops the endpoint confirming that another tenant's id exists.
State the engine behaviour instead of assuming it. Under READ COMMITTED the second UPDATE blocks on the row lock, and when the first commits PostgreSQL re-evaluates the WHERE clause against the newly committed row, so the version predicate now fails and the statement reports zero rows. Under REPEATABLE READ the identical collision raises SQLSTATE 40001 instead, so the handler must fold both shapes into one conflict response.
Keep UNIQUE (resource_id, version) even though the predicate already serialises writers. It is what makes a lost update unwritable if any other path ever reaches the revision table, and it converts a logic bug into 23505 rather than into a silently missing history row.

Follow-up

A client sends the version it read ten minutes ago and the resource has moved three versions. What is in your 409 so it can resolve the conflict without a full re-fetch?
Two editors, two disjoint fields, no overlap. Does your answer still refuse the second write, and should it?

Walk me through a complex technical project on your resume, specifically detailing your personal contributions

Medium · Resume & Past Project Deep Dives

Walk me through a complex technical project on your resume, specifically detailing your personal contributions and architectural decisions.

Approach

Fix the scope first: who calls this, how often, and what they do when it fails.
Name the read and write paths separately; they rarely have the same bottleneck.
Choose a partition key and say what query it makes expensive.
State the consistency you need, and where you are willing to be stale.

Follow-up

What breaks first when traffic grows ten times?
How does this behave when that dependency is down for an hour?

Can you explain a scenario where you had to adapt your software design to meet unexpected user or client const

Medium · Resume & Past Project Deep Dives

Can you explain a scenario where you had to adapt your software design to meet unexpected user or client constraints?

Approach

Clarify what is being asked and what a complete answer contains.
State your assumptions explicitly before working the problem.
Say what you would check first and why it is the highest-information step.
Work from the requirement backwards to the design.

Follow-up

What assumption would you test first?
How would you know your answer was wrong?

What specific technologies or software frameworks did you leverage in your previous internships or roles, and

Medium · Resume & Past Project Deep Dives

What specific technologies or software frameworks did you leverage in your previous internships or roles, and how proficient do you consider yourself in each?

Approach

Clarify what is being asked and what a complete answer contains.
State your assumptions explicitly before working the problem.
Say what you would check first and why it is the highest-information step.
Work from the requirement backwards to the design.

Follow-up

What assumption would you test first?
How would you know your answer was wrong?

How have you integrated specialized engineering tools, third-party APIs, or database scripts into past applica

Medium · Resume & Past Project Deep Dives

How have you integrated specialized engineering tools, third-party APIs, or database scripts into past applications?

Approach

Say who the caller is and what they do when the call fails halfway.
Define the identity of a request so a retry cannot double-apply it.
Separate accepted, pending, failed and confirmed; they are different facts.
Design the error taxonomy before the success shape; callers branch on it.

Follow-up

What happens if the caller retries after a timeout?
How does a client discover it is on an old version of this contract?

How do you structure a front-end web application (e.g., using JavaScript frameworks) to ensure responsive perf

Medium · Core Technical & Practical Domain Skills

How do you structure a front-end web application (e.g., using JavaScript frameworks) to ensure responsive performance and maintainability?

Approach

Clarify what is being asked and what a complete answer contains.
State your assumptions explicitly before working the problem.
Say what you would check first and why it is the highest-information step.
Work from the requirement backwards to the design.

Follow-up

What assumption would you test first?
How would you know your answer was wrong?

How do you approach writing clean, testable code when working on a tight schedule or delivering against a fixe

Medium · Core Technical & Practical Domain Skills

How do you approach writing clean, testable code when working on a tight schedule or delivering against a fixed questionnaire assessment?

Approach

Clarify what is being asked and what a complete answer contains.
State your assumptions explicitly before working the problem.
Say what you would check first and why it is the highest-information step.
Work from the requirement backwards to the design.

Follow-up

What assumption would you test first?
How would you know your answer was wrong?

Explain how you handle data validation and database integration when connecting software tools to legacy infra

Medium · Core Technical & Practical Domain Skills

Explain how you handle data validation and database integration when connecting software tools to legacy infrastructure databases.

Approach

Say who the caller is and what they do when the call fails halfway.
Define the identity of a request so a retry cannot double-apply it.
Separate accepted, pending, failed and confirmed; they are different facts.
Design the error taxonomy before the success shape; callers branch on it.

Follow-up

What happens if the caller retries after a timeout?
How does a client discover it is on an old version of this contract?

What strategies do you use to evaluate your own skill level across different programming languages and technic

Medium · Core Technical & Practical Domain Skills

What strategies do you use to evaluate your own skill level across different programming languages and technical toolsets?

Approach

Clarify what is being asked and what a complete answer contains.
State your assumptions explicitly before working the problem.
Say what you would check first and why it is the highest-information step.
Work from the requirement backwards to the design.

Follow-up

What assumption would you test first?
How would you know your answer was wrong?

Describe a situation where you had to debug an issue in a project that was already deployed or close to a dead

Medium · Resume & Past Project Deep Dives

Describe a situation where you had to debug an issue in a project that was already deployed or close to a deadline.

Approach

Establish what changed and when, before forming any theory.
Pick a bisection that eliminates candidates whichever way it turns out.
Check the instrumentation before believing the symptom.
Separate the trigger from the cause; the deploy is rarely the bug.

Follow-up

What would you look at first, and what would it rule out?
How would you tell a cause from a coincidence here?

Suggested practice checklist

Built from the rounds and topics HNTB candidates report.

Day 1 — Map the HNTB loop

Write out the reported sequence: Initial Conversation, Virtual Panel Interviews, Office Visit Invitation, Discussion with Leadership.
For each round, write one sentence on what it is judging, from the description above, and mark the one you are least ready for.

Deliverable: A one-page map of the 4 reported rounds, with the weakest marked.

Day 2 — Work Interview preparation (resume & background)

Spend the session on Interview preparation (resume & background), which HNTB candidates report being tested on.
Write one worked example in Interview preparation (resume & background) and time yourself on it.

Deliverable: One timed worked example in Interview preparation (resume & background).

Day 3 — Work Behavioral interviewing / storytelling

Spend the session on Behavioral interviewing / storytelling, which HNTB candidates report being tested on.
Write one worked example in Behavioral interviewing / storytelling and time yourself on it.

Deliverable: One timed worked example in Behavioral interviewing / storytelling.

Day 4 — Work Project-based technical discussion

Spend the session on Project-based technical discussion, which HNTB candidates report being tested on.
Write one worked example in Project-based technical discussion and time yourself on it.

Deliverable: One timed worked example in Project-based technical discussion.

Day 5 — Answer out loud: Resume & Past Project Deep Dives

Answer aloud, timed: Walk me through a complex technical project on your resume, specifically detailing your personal contributions and architectural decisions.
Answer aloud, timed: Can you explain a scenario where you had to adapt your software design to meet unexpected user or client constraints?

Deliverable: Spoken answers to 2 reported Resume & Past Project Deep Dives question(s), under time.

Day 6 — Answer out loud: Core Technical & Practical Domain Skills

Answer aloud, timed: How do you structure a front-end web application (e.g., using JavaScript frameworks) to ensure responsive performance and maintainability?
Answer aloud, timed: Describe your experience with CADD software, spatial data, or domain-specific technical tools mentioned in your application materials.

Deliverable: Spoken answers to 2 reported Core Technical & Practical Domain Skills question(s), under time.

Day 7 — Answer out loud: Behavioral, Culture Fit & Career Goals

Answer aloud, timed: Where do you see your career progressing over the next 5 years, and how does working at HNTB support that vision?
Answer aloud, timed: Describe a time when you had to manage competing priorities or handle significant work pressure to meet a project delivery deadline.

Deliverable: Spoken answers to 2 reported Behavioral, Culture Fit & Career Goals question(s), under time.

Behavioural preparation

Behavioural rounds judge the decision you made and what it cost.

Describe your experience with CADD software, spatial data, or domain-specific technical tools mentioned in you

Medium · Core Technical & Practical Domain Skills

Describe your experience with CADD software, spatial data, or domain-specific technical tools mentioned in your application materials.

Approach

Pick a story where you made the decision, not one where you watched it.
State the situation in two sentences and spend the rest on the reasoning.
Give the blast radius: what could have broken, and what you measured.
Name the disagreement and how you resolved it with evidence.

Follow-up

What would you do differently if you ran that again?
How did you know your change caused the improvement?

Where do you see your career progressing over the next 5 years, and how does working at HNTB support that visi

Medium · Behavioral, Culture Fit & Career Goals

Where do you see your career progressing over the next 5 years, and how does working at HNTB support that vision?

Approach

Pick a story where you made the decision, not one where you watched it.
State the situation in two sentences and spend the rest on the reasoning.
Give the blast radius: what could have broken, and what you measured.
Name the disagreement and how you resolved it with evidence.

Follow-up

What would you do differently if you ran that again?
How did you know your change caused the improvement?

Describe a time when you had to manage competing priorities or handle significant work pressure to meet a proj

Medium · Behavioral, Culture Fit & Career Goals

Describe a time when you had to manage competing priorities or handle significant work pressure to meet a project delivery deadline.

Approach

Pick a story where you made the decision, not one where you watched it.
State the situation in two sentences and spend the rest on the reasoning.
Give the blast radius: what could have broken, and what you measured.
Name the disagreement and how you resolved it with evidence.

Follow-up

What would you do differently if you ran that again?
How did you know your change caused the improvement?

What are your primary strengths and weaknesses as a software developer, and how do you actively work to improv

Medium · Behavioral, Culture Fit & Career Goals

What are your primary strengths and weaknesses as a software developer, and how do you actively work to improve your weak areas?

Approach

Pick a story where you made the decision, not one where you watched it.
State the situation in two sentences and spend the rest on the reasoning.
Give the blast radius: what could have broken, and what you measured.
Name the disagreement and how you resolved it with evidence.

Follow-up

What would you do differently if you ran that again?
How did you know your change caused the improvement?

Why are you interested in joining HNTB over other technology or engineering consulting firms?

Medium · Behavioral, Culture Fit & Career Goals

Approach

Pick a story where you made the decision, not one where you watched it.
State the situation in two sentences and spend the rest on the reasoning.
Give the blast radius: what could have broken, and what you measured.
Name the disagreement and how you resolved it with evidence.

Follow-up

What would you do differently if you ran that again?
How did you know your change caused the improvement?

How do you explain complex technical concepts or software features to team members who come from non-technical

Medium · Behavioral, Culture Fit & Career Goals

How do you explain complex technical concepts or software features to team members who come from non-technical civil or structural backgrounds?

Approach

Pick a story where you made the decision, not one where you watched it.
State the situation in two sentences and spend the rest on the reasoning.
Give the blast radius: what could have broken, and what you measured.
Name the disagreement and how you resolved it with evidence.

Follow-up

What would you do differently if you ran that again?
How did you know your change caused the improvement?