How great are tree grates?

DDOT will soon be bidding contracts to reconstruct 18th Street in Adams Morgan. Adams Morgan Main Street is trying to persuade them to replace the standard tree boxes with grates.

Tree boxes fence off an area for the tree’s soil and roots. Meanwhile, tree grates cover that space with a surface that people can walk on, but which allow rainwater to run down to the soil beneath.

DDOT’s Urban Forestry Administration generally refuses tree grates, though they already exist in some areas such as Georgetown and downtown, and are part of the new Columbia Heights public realm at 14th and Park Road.

According to a presentation on innovative stormwater techniques, grates will also be part of the reconstruction of 17th Street in Dupont Circle. The need is even more acute on 17th, where the sidewalks are extremely narrow. In many places, there isn’t even the standard 10 feet between fenced-off yards or sidewalk cafes and the adjacent tree boxes.

In Adams Morgan, DDOT will be significantly widening sidewalks, creating much more pedestrian space even with boxes. At the same time, 18th gets very heavy pedestrian traffic and more space would be helpful.

This problem is most severe on U Street. Unlike in Adams Morgan, DDOT’s plans for U Street don’t widen the sidewalk, except in one small spot, and U Street is growing rapidly in numbers of residents, retailers, and pedestrian traffic.

Why does DDOT oppose tree grates? Here are some arguments made by UFA head John Thomas in a May email on the subject:

1. DDOT’s ADA compliance officer does not accept tree grates. I am not an ADA expert, but it seems that tree grates are no worse than tree boxes, which block off the entire space to all people including those with disabilities. Also, DC has a number of tree grates now.
2. The grates are above the DDOT maintenance capabilities. This is a legitimate concern in most areas. DDOT does not have the ability to keep checking on tree grates. If not monitored, as the tree trunk expands, the grate can choke it unless the hole is widened. Also, roots can pop up the grate. Many (or perhaps all) of the existing tree grates in DC are in areas such as Georgetown and downtown where a BID can handle some maintenance. DDOT could require an agreement to maintain the grates from a local business or citizen association before agreeing to install any.
3. Trees will be damaged at the trunk and lower limb levels (as is the case along and M and Wisconsin) regardless of the grates. Thomas didn’t elaborate on why, though I could see that people might lean against the tree or bump it as they walk if the grates facilitate getting closer. In a place like Adams Morgan or U Street, drunk people might be more likely to lean against (or perhaps urinate on) the trees if they can get close to them.
4. Bikes tend to get locked to trees when tree grates are present. Fences and plants keep bikes away. Also a fair point.
5. The liability would still remain with the District even with an MOU if there is a trip/fall claim. Are grates less safe than fences? It’d be helpful to have any statistics from other cities or from DC’s existing grates versus its tree boxes.
6. UFA has historically denied grates across the board. So? DDOT also has historically granted curb cuts willy-nilly, but fortunately, they have recently cracked down. It shouldn’t ever be too late to change bad past practices.

Should DDOT install tree grates? There are good arguments on both sides. It seems that a decision about tree grates must balance the value of adding pedestrian space against the slightly better conditions for trees.

UFA is focused entirely on maximizing tree canopy, and that’s an extremely worthy goal. In some commercial areas, however, maintaining a wide enough sidewalk for pedestrians is also a worthy goal, and there needs to be a balance that weighs the inadequacy of pedestrian space with the potential harm to trees.

Plus, sometimes UFA can’t put in a tree, or has to settle for a smaller tree box, because of available space. Grates could allow more trees that can collect more stormwater. There are even more innovative stormwater techniques for trees, such as grates on hills (like 18th Street) where water from one tree area drains into the next, and so on, like a natural hill. DC also has “structural soil” covered with cobblestones or pavers to provide stormwater management without sacrificing walking space around the ballpark and Barracks Row.

All of these techniques, including tree grates applied where pedestrian volumes warrant, can make DC’s streets more usable and greener at the same time.