The Progressive Design-Build (PDB) model reconfigures how an agency structures decision-making, risk, and collaboration across the life of a capital project.

Progressive Design-Build is a two-step evolution of traditional design-build. In the first phase, the owner selects a contractor–designer team early, before the design is fully developed. Instead of locking a lump-sum price upfront, the parties work together in an open-book environment to advance design, validate assumptions, and progressively define cost. Only once sufficient design maturity and risk definition are achieved do the parties agree to a final price or target cost for delivery.

This sequencing distinguishes PDB from both traditional design-bid-build and conventional design-build, as it shifts the relationship from adversarial price competition to continuous alignment on scope, risk, and value.

Dee Leggett, Director of Business Operations at Herzog Transit Services explained:

Unlike traditional design-bid-build where designers are selected and then contractors come in later with a fixed price, progressive design-build brings the owner and contractor together much earlier and then locks in a price when much more of the design is defined.

The PBD delivery model was a recurring theme at the APTA Rail Conference held in Baltimore last week. Here, in a discussion sponsored by Stacy Witbeck, panellists emphasised that PBD works when it is treated as a management system, rather than a contracting label. Austin’s Project Connect light rail and Virginia’s Longbridge North projects were used as key case studies throughout this discussion.

Austin Light Rail rendering

© Austin Transit Partnership

For example, Lindsay Wood, Exec. Vice President of Engineering & Construction at Austin Transit Partnership explained that the model was chosen to “think differently about how we work together” when delivering the city’s light rail network.

Why Agencies Choose Progressive Design-Build

At the APTA Rail Conference, the panellists repeatedly returned to four drivers in their decisions to use the PBD model:

1. Early risk shaping instead of late risk transfer

Traditional design-build often pushes risk to the contractor after design is relatively advanced. PDB pulls risk identification forward. Instead of pricing unknowns early, teams jointly work through them.

2. Iterative estimating (“design to cost”)

Rather than a single fixed bid, cost is tested repeatedly as design evolves. This was emphasised strongly in both case studies as essential for complex rail infrastructure.

3. Stakeholder integration

In the case of the Virginia Passenger Rail Authority Long Bridge North programme, stakeholder complexity was extreme: multiple federal agencies, the National Park Service, local jurisdictions like Washington, DC, freight rail operator CSX Transportation, and transit users sharing constrained infrastructure.

Naomi Klein, Permitting & Stakeholder Senior Manager for the project, thus described a system where “there was no such thing as too much communication.” However, communication also had to be disciplined to avoid overwhelming stakeholders with fragmented requests.

4. Flexibility under construction constraints

For the Long Bridge North project, rail traffic had to remain live while replacing and expanding bridge structures over the Potomac River corridor. That constraint alone made late-stage redesigns or rigid upfront pricing impractical.

What Makes it “Progressive”?

An important clarification from the panel was that “progressive” does not simply mean “phased.” It means the commercial and technical relationship evolves together.

In Austin’s light rail project, Brad Cummings, Senior VP, Procurement & Contract Management at Austin Transit Partnership, highlighted how early work packages were used strategically. For example, they carried out early tree clearing constrained by environmental windows and commenced partial steel procurement before full design completion. This reflects a key PDB principle, where you don’t wait for design to be 100 percent completed to begin controlled, low-risk execution.

Similarly, permitting strategies can also be reshaped through the PBD delivery model. On Long Bridge North, permitting was coordinated at a higher level so that agencies could approve broader scopes of work upfront, with incremental approvals as design packages matured. This reduced duplicate reviews and helped keep construction moving while maintaining regulatory compliance.

The discussion at the APTA Rail Conference also highlighted that PDB requires a different internal governance model. Austin Transit Partnership described restructuring decision-making so that authority sits closer to delivery teams, with clear escalation paths rather than layered approval bottlenecks. Weekly decision cycles, task forces, and co-located teams were used to prevent the “everything climbs to the top” problem that often slows traditional delivery.

The Trade-Off: Uncertainty Traded for Adaptability

Progressive Design-Build is not a cost-certainty model at the start. Instead, it is a cost-discovery model with structured control mechanisms. Owners accept less early price certainty in exchange for:

• Earlier problem detection
• Fewer redesign cycles in construction
• Better alignment of scope and funding reality
• More defensible final cost decisions

This only works if cost containment is continuous. Both Austin and Virginia teams emphasised the importance of shared risk registers, iterative estimating checkpoints, and disciplined scope validation as design progresses.

Meanwhile, the uncertainty that arises for transit agencies through the PBD model is largely unavoidable. Indeed, in a separate discussion focused on delivering rail expansion projects, Jessica Mefford-Miller, Chief Executive Officer at Valley Metro, indicated that in the current volatile market, contractors don’t want to take on conventional Design-Build contracts. A project using this model may therefore only receive one bid, and costs will be hiked to cover the risk.

Instead, PBD offers a more feasible way forward for all parties involved. However, Mefford-Miller also stressed the necessity of ensuring PDB partnerships stay productive, as the model cannot work with antagonistic relationships.

Michael Rothenheber, Senior Vice President at Johnson, Mirmiran & Thompson reaffirmed this message:

You have to have the right contractor and the right design team who have the mentality to take on things that are not always black and white. If your mindset is purely linear—point A to point B—this kind of delivery model is going to be very challenging.

So What Exactly is Progressive Design-Build?

For both Austin Transit Partnership and the Virginia Passenger Rail Authority, Progressive Design-Build is a deliberate restructuring of how large infrastructure projects absorb uncertainty.

At its core, Progressive Design-Build is a collaborative delivery model where the owner and integrated design-builder are selected early, then jointly develop the design, validate scope, and manage risk through iterative, open-book estimating before agreeing to a final delivery price. This process is supported by governance structures that prioritise shared decision-making over contractual adversarialism.

The model therefore replaces “bid and build” with “decide and build together.”

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