Pavement Design

Pavement Design | LCCA Projects

Metro District LCCA Projects

Metro District Comments

SP 2738-31, MN 101, Letting date 1/19/2027

Comment from Daniel Labo, Concrete Paving Association of Minnesota, djlabo@cpamn.com, 12/31/2024

Regarding the Bimunious Design:
The initial design life for the bituminous Mill and Overlay is listed at 20 years. The ESAL estimator indicates that it is classified as a high ESAL roadway (>5m 20-year Flexible ESALS) and the thickness is >4”. Per Table 440.1 of the Pavement Design Manual, this overlay should last between 12-16 years assuming the existing surface condition is good, if poor, it should be between 9-13 years. A good approximate median value is 12 years, which is substantially less than the 20-years of life the overlay is given credit for in the LCCA for the first fix.

The second repair is a 2” mill, 4” overlay. This fix is given a 17-year lifespan, and Table 440.1 indicates it should be around 11-years on average.

The third repair is a 2” mill, 4” overlay. This fix is given a 17-year lifespan, and Table 440.1 indicates it should be around 11-years on average.

This begs several questions. Why is the District assigning unrealistic pavement design lives to the bituminous designs within the LCCA? Under no circumstances do these design lives correlate to the pavement design manual, and the effect is that the LCCA is entirely failing to account for whole Mill & Overlay projects within the LCCA. By my calculations, this will add at least $1.5 million to the NPV, raising the total NPV of this option to at least $4.5 million.

Additionally, how does the district intend to Mill 2” and Pave 4” multiple times without needing to regrade the shoulders to account for the grade raise?

Regarding the Concrete Design:
There is no need to fully replace the grade on the mainline or shoulder, as a mill and inlay design will work just fine. Milling 8” of bituminous out on mainline and paving 10” of concrete will work great (widened lane design, 13' per lane). The shoulders can be then milled 2” and paved 4” to match the elevation. This change would reduce the NPV of this option to approximately $3.75 million.

Overall comments:
By properly calculating the bituminous design life, and using a slightly modified concrete pavement design, the concrete option will become the lowest NPV option. Specifically, the bituminous option will be about 120% of the low-cost concrete option. This ignores the fact that the Discount Rate deviates from the current pavement manual calculation as well (it should be 1.14%, not 3.10%), which would make the difference even larger. When the district adjusts the bituminous and concrete designs, will you please post the revised calculations please?

Additionally, considerations should be given for corridor pavement continuity. The pavement to the north of this project is concrete, and I-94 is the primary connector traffic-wise to this project to the south, which is also concrete. High volume roadways are outstanding places to build concrete to minimize life cycle construction impacts, and these types of roadways are traditionally built with concrete.

Thank you for allowing us the opportunity to comment on this LCCA, and we hope to see revisions made to account for the errors found in the LCCA file posted for public review.

Pavement Design Engineer response

pending

SP 6220-96, US 61, Letting date 9/24/2027

Comment from Daniel Labo, Concrete Paving Association of Minnesota, djlabo@cpamn.com, 12/31/2024

For the concrete design shown, you assume a tied shoulder and it resulted in an 8.0” pavement [initial cost = $9,122,157.48]. If one were to move the shoulder joint away from centerline by 1’ (a negligible cost change by adding 2 dowel bars/joint). The resulting 20-year concrete pavement thickness would drop to 7.0” [initial cost = $8,184,862.66]. This would reduce initial costs by $937,294.82 alone. While this strategy alone would not result in a change, it will be coupled with other strategies discussed below.

As there is no benefit of having a tied shoulder in the LCCA, CPAM proposes that all options consider utilizing a widened lane design throughout.

The discount rate shown does not correspond to the guidance in the current pavement design manual; according to my calculations it should be 1.14%.

Optimized Design Proposed: To increase initial cost savings, we propose modifying the construction to also use as much of the in-place shoulder as possible in lieu of the full replacement shown in the concrete design. A mill and inlay concrete pavement can be used with widened lanes, the shoulders can have a simple 1.5” bituminous mill and overlay to extend their life, and it negates the need to raise the final pavement grade.
Optimized Design Initial Cost: $7,186,400.27 [anticipated savings of $1,935,757.21 vs 20-yr design shown]. This represents an initial cost per year of design life of $205,325.72.
Optimized LCCA net result: Due to various general comments below, it is not possible to accurately analyze. Please make corrections and revise and resubmit for industry review, as it is expected that 35-year design is likely highly competitive under an optimized scenario. However, when comparing the initial cost per year of design life, the 35-year concrete pavement would be a 60% reduction in this important metric.

General comments:

1. The discount rate shown does not correspond to the guidance shown in the current pavement design manual. Before commenting, I asked the pavement design office, and they said a change was made ‘in the spirit of cooperation and simplicity’ and the pavement manual would be updated in the future. The 5-year rolling average method shown in the pavement design manual represented a compromise between MnDOT, CPAM, and MAPA. The LCCA law requires a spirit of collaboration between MnDOT and industry as part of performing LCCA’s, and this unilateral action is anything but collaborative. CPAM was not consulted on a potential change, it was simply thrust upon our respective industries. Please explain why this long-standing agreement was scrapped, when the pavement manual will be updated, and what steps will be taken to ensure MnDOT follows the spirit of the law. Further, please unlock the discount rate field in the file for public review, as it is not possible to analyze options with the correct rate.
2. The maintenance cycles for concrete pavements appear to be substantially out of date. When were these cycles last reviewed and updated by MnDOT? As MnDOT knows, substantial changes were made to concrete mixes in the 1990’s, and these pavements are substantially outperforming concrete pavements constructed before the change.
3. MnROAD testing in the 1990’s showed no difference in performance between a widened lane and a traditional 12’ lane; why are these MnROAD findings not being incorporated into the MnPAVE software?
4. It appears that design optimization of the concrete section was not performed. CPAM is happy to assist in reviewing the proposed section prior to running the LCCA, which could negate many/all comments in the future.
5. It appears that MnDOT is following the guidance of Table 730.2 in the pavement design manual. However, the 4” mill and overlay is shown as a 20-year design life. This is a dubious design life expectation (which Table 440.1 would agree with), but assuming its correct, table 730.2 would actually apply as it is for all pavements for a DL>=20 years (all bituminous design lives are 20 years as shown). Please analyze a 35-year option as required and resubmit the LCCA for public review, as required by table 730.2, and update the LCCA to the correct 50-year analysis period. If the mill and overlay design life is in error, please provide the correct design life as part of the response and commentary on how it impacted the LCCA.
6. Traffic growth rate. For flexible pavement, it is 0.49%, and for concrete it is 1.0%. Why is this different?
7. MnPAVE was never developed to design asphalt overlays. Where is the support documenting the use of MnPAVE for asphalt overlays? Per the pavement manual, it should have a design life of about 6-12 years. Assuming a 9-design life, the initial cost per year of design life would be $508,385.09/year of design life.

Pavement Design Engineer response

pending

SP 1929-50, MN 77, Letting date 3/27/2026

SP 1926-23, MN 316, Letting date 12/6/2024

SP 2713-129, US 12, US 12, Letting date 9/26/2025

Comment from Brandon Brever, Minnesota Asphalt Pavement Association (MAPA), bbrever@mnapa.org 10/31/2024

Minimized Local Disruption: Asphalt paving allows work to be completed in phases with fewer extended closures. This speed of construction means that local traffic, businesses, and communities experience fewer disruptions. Asphalt can be paved in short time windows (overnight or during off-peak hours), which is less disruptive to daily routines and minimizes impacts on local commerce, something particularly important in business corridors. Asphalt can be used by traffic almost immediately after compaction, ensuring minimal downtime.

Efficient Maintenance with Traffic Open: Over a pavement’s life cycle, asphalt maintenance can be executed with minimal impact to traffic. Asphalt overlays, scheduled at intervals like year 20 and year 37, can often be applied while keeping lanes open, allowing for a smoother driving experience with fewer full closures. In comparison, the concrete life cycle requires major concrete pavement removal and replacement at year 20 and 35.

Enhanced Ride Quality Over Time: Asphalt overlays improve ride quality during maintenance without requiring extensive reconstruction. Asphalt’s smooth surface ensures consistent ride quality and addresses minor defects efficiently. This is beneficial for the traveling public by providing a smoother, quieter driving experience.

Select Granular Base Requirements:
Another key point to consider is the difference in base requirements. The asphalt alternative includes a 22-inch select granular sand subbase, compared to the 12-inch select granular subbase for concrete. This thicker granular base provides additional flexibility and strength, contributing to a more stable and durable foundation over time. The increased base depth with asphalt serves to enhance drainage and prevent subgrade issues, especially in regions prone to freeze-thaw cycles, which can cause pavement heaving and cracking. This extra base support not only extends the life of the pavement but also helps reduce maintenance needs by preventing early-stage foundation issues. In addition, the thicker base can help distribute loads more effectively, and limit the amount of strain in base layers. This contributes to long-term quality and provides a robust structure that can then limit any distress to the top layers of asphalt. Mill and overlays can then be used at typical intervals to prolong the overall structural integrity of the section.

Environmental & Resilience Benefits:
HMA pavements are compatible with high recycled content (100% of asphalt pavements are recycled), contributing to sustainability goals. Utilizing RAP (Recycled Asphalt Pavement) aligns with environmental objectives by reducing the demand for virgin materials and lowering carbon emissions associated with production. With climate resilience becoming a significant consideration, asphalt’s adaptability to various weather conditions and potential for innovative additives (e.g., warm-mix asphalt technology) make it a forward-looking choice. The choice of HMA aligns with future requirements to adjust to evolving climate conditions or state and federal funding priorities that prioritize resilient infrastructure.

While continuity along corridors is desirable, other factors like business impact, community access, and reduced congestion are vital to consider in urban and suburban settings. Given these benefits, asphalt provides an efficient, adaptable, and locally sensitive solution that supports businesses, keeps traffic moving, and can be maintained with minimal disruption over its lifecycle.

Pavement Design Engineer responses, 11/25/2024

"In comparison, the concrete life cycle requires major concrete pavement removal and replacement at year 20 and 35."

Response: The concrete life cycle requires Concrete Pavement Rehabilitation (CPR) at years 20 & 35, there is no concrete pavement removal in the 50-year analysis period when the concrete design life is 35 years.

"Select Granular Base Requirements..."

Response: Select granular sand subbase is a structural requirement and reduces stresses and strains on the subgrade, especially during spring thaw. Due to the load-bearing characteristics of concrete pavement a thinner subbase section can be used.

"While continuity along corridors is desirable, other factors like business impact, community access, and reduced congestion are vital to consider in urban and suburban settings..."

Response: Continuity along corridors also helps with more uniform snow and ice control since bituminous and concrete are treated differently from late fall to early spring.

SP 0208-169, MN 65, Letting date 2/1/2026

Comment from Dan Labo, P.E., Concrete Paving Association of Minnesota (CPAM), djlabo@cpamn.com 10/8/2024

This is within 10% on the LCCA (even with 6” concrete shoulders vs 4” asphalt shoulders). I know the locals tend to prefer concrete, so I’m hoping the final pavement selection is the concrete option? Please confirm, and if nothing else, we definitely want alternate bid if not concrete pavement outright.

Pavement Design Engineer responses 11/5/2024

"I know the locals tend to prefer concrete, so I’m hoping the final pavement selection is the concrete option?"

Response: The final pavement selection will be the low cost option of bituminous.

"Please confirm, and if nothing else, we definitely want alternate bid if not concrete pavement outright."

Response: The district will be requesting an exception from alternate bid. Ultimately, after discussion with agency stakeholders and consideration of project schedule and budget, it was agreed that maintaining diligence in delivering this project and achieving the expected corridor safety improvements is a top priority. Please note that future alternate bid opportunities are being reviewed by the district.

SP 1923-48, MN 50, Letting date 12/5/2025

Comment from Dan Labo, P.E., Concrete Paving Association of Minnesota (CPAM), djlabo@cpamn.com 10/8/2024

It looks like the ‘whitetopping’ option is 7” for a 20-year concrete design. 4” of bituminous get’s 20-years too, so this LCCA is obviously wrong. I’d imagine a true 20-year concrete whitetopping would come in about 5-5.5” thick, and the 7” is at least a 35-year design (it should get credit for that at least). This job highlights the bigger issue I’ve mentioned before of the new MnPAVE rigid only outputting 7” minimum pavements. Please let me know when a corrected LCCA will be issued, as this one is pretty egregious.

Pavement Design Engineer responses 11/5/2024

"4” of bituminous get’s 20-years too, so this LCCA is obviously wrong."

Response: This project is a 4” mill & 4” HMA overlay. The expected life of a 4” mill and 4” HMA overlay is less than 20 years on this aged pavement structure. Per the PDM Section 710, all HMA overlays 5.0-inches or less are included in the DL <20 years. Related to consideration as a 4” HMA reconstruction, a 4 inch design will not satisfy MnPAVE requirements.

"I’d imagine a true 20-year concrete whitetopping would come in about 5-5.5” thick"

Response: A BCOA-ME design comes out at 4.5 inches and a revised LCCA shows the 4.5” PCC whitetopping is 137.7% higher than the low cost alternate #1.

"This job highlights the bigger issue I’ve mentioned before of the new MnPAVE rigid only outputting 7” minimum pavements."

Response: MnPAVE Rigid is based on doweled PCC pavement from MEPDG 1.1 and CPAM did not want 6-inch doweled PCC pavement.

"Please let me know when a corrected LCCA will be issued, as this one is pretty egregious."

Response: You are welcome to present your own LCCA with supporting data for this project.

SP 1002-124, MN 5, Letting date 6/30/2025