Do you really need an engineer to design your trail?
September 25, 2014
Several years ago, I met Fred Meijer at a meeting. Mr. Meijer was well known for his philanthropy, especially in the development of bicycle paths across West Michigan. When he found out that I design these paths, he baitingly asked me, “Why do we need an engineer to design bike paths?” I gave him all of the standard engineer answers about drainage, road right-of-ways, easements, retaining walls, and good construction oversight. He smiled at my answer, having known it ahead of time. But the question stuck with me. Why should someone invest in good engineering design and oversight on a bike path? They’re simple, right?
I will answer the question with an example.
Sometime back a Township client asked this same question, and, despite my good “engineer” answer, decided that rather than accepting my proposal they would just have a local developer build the trail. It seemed like a good idea to them at the time. They saw the initial cost savings of removing the engineering independent design and construction observation from the project budget.
Fast forward five years. the same Township called me to design an extension to their developer-built trail. They also requested that I take a look at the existing trail section, admitting that it needed significant maintenance, and that they wanted my advice on how to fix it. The photos below show what went wrong with the original trail.
The old trail is peppered with cracks. Why? Here are my thoughts:
- Design for each trail is site-specific. There is no “typical cross section” that can be constructed everywhere. Each section of trail has its own unique design and construction challenges that must be carefully reviewed to ensure that the trail lasts as long as possible.
- Construction oversight is critical. Contractors and developers construct. Engineers design and work to make sure the design is implemented in the field. Some of the most common problems are smooth curve radii, improper slopes, poorly compacted gravel, incorrect asphalt thickness and temperature, and drainage.
- Asphalt pavement relies heavily on a good base to perform properly. Good pavement design considers the asphalt mix, the gravel quality, gradation and thickness, and the level of compaction beneath it.
- Drainage is critical–for both surface water crossing the trail and sub-base drainage under the asphalt. If these issues are not properly addressed, the surface will not last.
- The pavement for this trail was constructed in one layer. This may have seemed like an easy way to cut cost from the project, but we learned long ago that it takes two asphalt layers to build a lasting, low-maintenance trail. Two layers of asphalt provide a significantly smoother and stronger trail with minimal increase in cost.
- Weeds and roots are growing through the asphalt. Often in situations like this, it helps to place a Bio-Barrier type product below the trail surface to prevent vegetation growth.
Below is a photo of the new trail section for which Prein&Newhof provided design and construction observation services. It should last for many years before needing anything beyond normal maintenance.
Over the past few decades and several hundred miles, Prein&Newhof has learned much about good trail design. Good engineering makes a real, tangible and positive difference in the outcome of a trail. It is well worth investing a little more to make sure your community’s trail is done right. The next time someone asks about the value of an engineered design, I’ll have more to say!