Yesterday evening, I attended the Carrboro Town Council meeting to ask Town Council to amend their list of projects submitted for state funding to DCHCMPO by June 27, 2023 in order to include the Bolin Creek Greenway (BCG) in the list.

A homeowner who is a member of the Friends of Bolin Creek criticized the Mayor for this recent tweet below, and recounted some of the criticisms directed at anti-BCG homeowners in a recent post at Triangle Blog Blog.

The speaker made several statements about the importance of getting facts right, and then engaged in the exact behavior that the Mayor warned about – making wildly misleading statements about the potential project cost of the BCG. The remainder of this blog post unpacks those statements and addresses what the BCG is likely to cost.

The speaker cited an article from Maryland about a greenway that cost $82.5 because it had an underground tunnel under downtown Bethesda (pic below – doesn’t look much like Bolin Creek), which is some of the most valuable real estate on the East Coast and a labor market with much higher construction costs than Carrboro. A tunnel under these buildings for anything will require life safety measures, evacuation points and be very expensive.

The speaker then stated that the Bolin Creek Greenway may have a similar cost to the Bethesda project, even though none of the BCG would be in a tunnel or be in an environment like this. The speaker then asserted, without any evidence, that the BCG would cost as least much as the library being built in Downtown Carrboro. Even if we ignore the ridiculous Bethesda comparison, given the price of the library, the speaker is therefore suggesting the BCG will cost (at minimum) over $41 million dollars.

THIS IS NOT A REMOTELY REASONABLE NUMBER. So let’s take a considered look at what BCG Phases 3 and 4 might actually cost.

But first, a disclaimer – this is a simple exercise using online data sources. This is not in any way a substitute for real engineering design and cost estimating work. However, this is an attempt to model how real cost estimates are developed and managed to help the community understand how these methods can support the Town in making informed decisions.

How Infrastructure Professionals Create Cost Estimates

When a city or town engineer, or engineering consultant puts together a cost estimate for a project, the best information comes from having a preliminary design that is specific to where the proposed infrastructure will be on the earth.

Sometimes technical professionals get asked to put together a cost estimate for something without a preliminary design. This is inherently a more uncertain proposition. Responsible analysis of this type involves identifying projects that have a similar physical nature to the proposed project, examining their cost estimates, and using per linear foot costs for facilities like greenways and streets, and then reporting not one number, but a range of potential cost outcomes.

Applying These Two Approaches to the Bolin Creek Greenway

Let’s start with the Bolin Creek Greenway Master Plan from 2009. It has a preliminary conceptual design with significant detail. Its cost estimate is specific to the land along Bolin Creek, described as follows:

“For conceptual planning purposes, budget estimates prepared for this plan assumed a primary trail surface of concrete in creekside/flood prone areas and asphalt for hillslopes and upland areas.”

Let’s take a look at what the 2009 study estimated for Phase 3 of the creekside alignment for the BCG. (page 86 in the Master Plan) This is the Carolina North Forest Section.

This estimate uses detailed cost components and has a total cost of roughly $1.3 million for 1.77 miles of greenway in Phase 3.

Here’s the Phase 4 cost estimate – which extends from the southern end of Phase 3 to roughly Estes Drive.

This estimate also uses detailed cost components and has a total cost of roughly $1.1 million for 1.26 miles of greenway in Phase 4.

But These Costs Are Fourteen Years Old! Can We Still Use Them?

It’s not ideal to work with old numbers. We can consider these numbers if we add some extra contingency for caution and account for inflation. Here’s how.

The note at the bottom of both cost estimates says that land acquisition and several other costs are not included. It’s hard to say exactly how much we would want to raise the overall presumed cost for each of these “does not include” items. However, a conservative approach to adding a contingency budget would add 45% to the base cost. The original BCG budget adds 15%.

Let’s quickly calculate two higher contingency costs. Here’s the math:

The base cost for Phase 3 is $1.12 million before adding contingency. Instead of 15%, if we add 30% and 45% contingency we get:

• With 30% Contingency: $1.12m + $336,000 (30% of $1.12m) = $1,456,000 for Phase 3.
• With 45% Contingency: $1.12m + $504,000 (45% of $1.12m) = $1,624,000 for Phase 3.

Now let’s do the same for Phase 4. Phase 4’s base cost is about $948,000 before adding contingency. If we add 30% and 45% contingency we get:

• With 30% Contingency: $948,000 + $284,400 = $1,232,400 for Phase 4.
• With 45% Contingency: $948,000 + $426,600 = $1,374,600 for Phase 4.

Now we sum the costs by contingency level. At 30% contingency, the total 2009 cost for BCG Phases 3 and 4 would be $2,688,400. Let’s round up and call it $2.7 million for 3.03 miles.

At 45% contingency we get $2,988,600. Let’s round up and call it an even $3.0 million in 2009 dollars.

Next we account for inflation using a nifty tool like this.

Our 30% contingency estimate of $2.7 million in 2009 gets inflated to $3.8 million in 2023.

Our 45% contingency estimate of $3.0 million in 2009 gets inflated to $4.2 million in 2023.

We get a range of $3.8 million to $4.2 million in 2023 dollars for Phase 3 and Phase 4 of the BCG. If we wanted to work with rounder numbers, we might simply say $3.5 to $4.5 million for roughly 3 miles of trail. This is $1.2 to $1.5 million per mile.

Is $1.2 to $1.5 million per mile reasonable for the BCG in 2023? Let’s do Peer Review.

Instead of only working with this cost estimate, we can look at other greenway project cost estimates in the public domain that (this is really important) have similar phyiscal characteristics to the BCG.

The Capital Area Greenway Master Plan from Raleigh in 2022 has these costs per mile.

• Barwell Road Greenway: $7.4 m over 1.86 miles = $4 million per mile in 2025 dollars
• Brier Creek Loop: $12.2m over 3.57 miles = $3.4 million per mile in 2025 dollars

Both of the above include significant boardwalk segments, which are 7 times more expensive than asphalt on earth, the primary surface in those cost estimates. Neither of the cost estimates above for BCG Phases 3 and 4 identify boardwalk construction. Only one bridge of $75,000 is anticipated for BCG. The BCG corridor is in a relatively flat easement using pavement while up to 1/3 of a mile of the two facilities above are built on boardwalk. So these Raleigh cost estimates are probably high. If we converted the boardwalk sections of these two projects above to trail asphalt, Barwell Rd drops to $5.6 million over 1.86 miles for $3 million per mile, and the Brier Creek Loop drops to $10m over 3.57 miles, or $2.8 million per mile in 2025 dollars.

If we assume 3% inflation between 2023 and 2025, then these projects would be $5.3 million ($2.8m per mile) and $9.4 million ($2.6m per mile) in 2023 dollars.

A closer to home cost estimate is the estimate for Phase 2 of the Morgan Creek Greenway in Carrboro. It estimates the 1.2-mile segment had a construction cost of $912,000 million in late 2022. Inflation would raise this slightly to $932,000 in 2023 dollars. This is just under $800,000 dollars per mile. Pretty inexpensive!

Reasonable Estimates Use Ranges: BCG Phases 3 and 4 Could Cost Between $3 million and $9 million Dollars

If we take the per mile costs of these different sources in 2023 dollars we get a low of $800,000 per mile for Morgan Creek and a high of roughly $2.7 million per mile for two projects in Raleigh. For a 3.03-mile stretch of the BCG, that’s about $2.4 to $8.1 million dollars in total to build Phases 3 and 4 of the BCG.

What If Inflation Spikes Again?

It’s been a very unusual few years in financial markets. Will inflation increase, driving up material prices? Who knows? This is why you put contingencies on numbers. Want to try to add some extra contingency to account for this?

Let’s just bump both numbers up a little and finalize our numbers to say that the total cost to build Phases 3 and 4 of the BCG will most likely be between $3 million and $9 million.

This is a wide range – because there are many unknowns about the project even though we have a reasonably detailed preliminary design. As design of the BCG advances, factors other than inflation could also be a factor. The cost could fluctuate if different materials were used, or if there were requests to make more connections from additional neighborhoods to the greenway, those additional pieces could add cost. As design advances, more implementation issues will be identified and favorably resolved, the alignment will be confirmed, and the cost will stabilize in a much narrower range than above. This is the nature of all linear transportation projects.

Nice Things Like Greenways Cost Money

I’m sure that as different people read this post, some will find $3 million to $9 million to be a great value for the Town of Carrboro, and others will find it a waste of money. Those are value judgments, not fiscal ones. The Town of Carrboro’s Capital Budget was $68 million over 5 years in the last Capital Improvement Plan, up from $58 million for the prior 5-year period.

If the cost of BCG Phases 3 and 4 do fit within the $3 to $9 million range, this is a cost that is within the regular scale of expenditures of the Town’s 5-Year capital plans, and is not going to significantly impact the amount of debt the town manages. It is also worth noting that there are federal funds that can help pay for the BCG, and this is typically how Carrboro constructs such facilities in town.

Hopefully this analysis is reassuring to those who have a good faith curiosity about how much it costs to build a greenway.

What To Do About Misinformation: Don’t Get Distracted and Keep Moving Forward

The assertions by yesterday’s speaker that the BCG will cost somewhere between $41 and $82 million are fundamentally inaccurate. The suggestion that the BCG poses a significant risk to town debt finances is uninformed at best. It’s disappointing that anti-greenway homeowners have decided to engage a community conversation in this way. But based on how many conversations proceed in our community, we can expect these inaccurate figures to continue to circulate. We need to refer back to primary source and other relevant documents, ignore the noise, and keep moving.

As a resident who enthusiastically wishes to see the BCG built, I will continue to do my best to share accurate information, cite sources, show my work as done above and explain my methods.

My hope is that sometime this fall, the Town will restart the project and we can get a refreshed BCG conceptual design and new, up-to-date, fully vetted capital costs by early 2024.

Thanks to everyone who read to the end!

Closing disclaimer – this is a simple exercise using online data sources. This is not in any way a substitute for real engineering design and cost estimating work. However, this is an attempt to model how real cost estimates are developed and managed to help the community understand how these methods can support the Town in making informed decisions.