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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.

17th Street grates. Image from DDOT presentation (PDF).

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:

"Stormwater friendly tree box" from DDOT presentation (PDF).
  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.

David Alpert is the founder of Greater Greater Washington and its board president. He worked as a Product Manager for Google for six years and has lived in the Boston, San Francisco, and New York metro areas in addition to Washington, DC. He now lives with his wife and two children in Dupont Circle. 


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rant on: somebody, we will look back at ADA as the final sign of decadence in the 20th century consumer society. Luxuries we can't afford as it makes everything far more expensive. rant off

the problem (?) of anchoring cycles to trees might be solved if there were more bike racks....

by charlie on Jun 15, 2010 2:03 pm • linkreport

I've been looking for current renderings of the Adams Morgan streetscape project. I recall seeing some earlier in the process but I'm not sure what was approved and what wasn't. For instance orginally the sidewalks were to be the pebble surfaced sidewalks like those that have already gone in at Adams Mill by the exxon. But I'm hearing that the sidewalks will be different now? The original plan also called for a median on columbia road to be planted with trees. Is that still the case? will the streetscape include columbia rd between 16th and 18th? Sorry for the ramble but can't seem to find any current info.

by John on Jun 15, 2010 2:19 pm • linkreport

I've locked to the tree box fences in AM many times;there simply aren't enough bike racks for the summer crowd. Also,given the amount of inebriated people in AM,I would think the fences would at least give the smaller trees some protection from being knocked over/damaged.

by dynaryder on Jun 15, 2010 2:25 pm • linkreport

Tree grates are great even without trees:

by Lucre on Jun 15, 2010 2:26 pm • linkreport

ADA on gratings: [gratings in walking surfaces]...shall have spaces no greater than 1/2 inch wide in one direction. If gratings have elongated openings, then they shall be placed so that the long dimension is perpendicular to the dominant direction of travel.

Trying to picture a typical tree grate, but don't they tend to have concentric rings of openings? I could see how that fails the "direction of travel" clause. Also, 1/2 inch is pretty small for a slot.

by Lou on Jun 15, 2010 2:30 pm • linkreport

Some cities place trees into little cut-outs in the parking lane. It only takes up a small bit of parking (one-quarter to one-half of a car), but it might serve as a good compromise.

by Eric F. on Jun 15, 2010 2:31 pm • linkreport

If they really want to do something for the disabled how about making all building entrances on a block open at the same amount of inches from the curb.

Going on many streets with a wheelchair or blind is horrible. The streets are never level; you can not walk two blocks in the city (except for some places downtown) without running into a non-level sidewalk due to horrible construction, negligence, or tree roots.

The other problem is the buildings since U street was mentioned in the post lets use that. The southern portion of 1300 block of Ustreet between 13th street and the Nail salon is fine but then you reach the steps of the old Rowhouse which blocks up space; it causes people whether walking or in a wheelchair to use a tiny space to walk through then after those houses the space widens again. The space between the Rowhouses is not level and there is not enough space for a wheelchair.

Brick sidewalks look nice but cause tripping and falls all the time due to lose bricks. If they can fix all lose bricks in a timely manner go ahead and build them otherwise use something else. Looks aren't important as safety

by kk on Jun 15, 2010 2:35 pm • linkreport

Why are trees on sidewalks in the first place? There's much more space for them in the street.

by tom veil on Jun 15, 2010 3:15 pm • linkreport

Thank you for this post. As the Director of Planning and Design at Casey Trees, I think of tree grates more often than many people. To design great pedestrian friendly streets, large canopy trees are critical. You may notice that few people walk down streets without the shade trees provide in the summer (and that often people select the shade of a tree over a seat in the bus shelter). So when designing for street trees, we cannot ignore the impact tree grates often have on the critical root zone and trunk flare of the tree. Tree grates can restrict the growth of the tree and this damage can prevent street trees from maturing. When trees fail to mature, many of the environmental and social benefits of trees are not achieved. So tree grates should only be used when properly designed and where funding for maintenance is available.

by Maisie Hughes on Jun 15, 2010 3:49 pm • linkreport

Maintenance is really the key, whether you're talking about grates or whether to plant a tree in the first place. If nobody waters it or remembers to change out the grate, it will die. Period. So unless you have a high degree of confidence that it will be maintained, you should go with a lower maintenance tree without a grate.

by Reid on Jun 15, 2010 3:56 pm • linkreport

on a tangent to Maisies comment. DC's new bus shelters basically act as a toaster oven on hot sunny days. They also provide much less shelter from rain than the old ones. Major fail in my book. on my commute home NOBODY opts to sit in the bus shelter. Its actually a funny sight. Everyone standing around it seeking shelter everywhere BUT the shelter. Anyway. Sorry for the side rant.

by John on Jun 15, 2010 4:01 pm • linkreport

@ Maisie -- How to tree grates compare to tree boxes that people trample all over anyway?

by ah on Jun 15, 2010 4:07 pm • linkreport

There are a lot of "IF"s in the arguments for tree grates.

A tree grate should be allowed:
IF there is otherwise not enough room in the sidewalk, AND
IF there are plenty of bike racks, AND
IF a BID can and will handle the maintenance, AND
IF the grate has ADA compliant gaps, AND
IF the sidewalk is constructed using structural soil, AND
IF all future repairs of utilities under the sidewalk replace the structural soil, AND
IF the grate is installed properly so that it never pops up and creates a trip hazard, AND
IF, well, you get my point.

As a Landscape Architect, I avoid specifying tree grates as much as possible. The only time I prefer them is in situations on crowded sidewalks, where open tree areas would get trampled and kill the tree anyway. I agree with many of John Thomas' points.

(haha, captcha = beatnick secessionists)

by Larchie on Jun 15, 2010 4:25 pm • linkreport

While in general I could be swayed either way, when it comes to U Street I become a definite tree grate fan... the sidewalks are far too tight, especially on a Thurs/Fri/Sat night.

1 - One possible explanation: it's easier for visually impaired to detect a fence (as shown in the image) rather than a grate being uplifted by growing roots; and the potential tripping hazard they could cause. On a similar line of thought, however, I often witness those with adequate vision failing to spot those 1-2 ft high tree fences... and I've been guilty of this, myself, on a couple occasions.

2 - Agreed: there are plenty of uplifted grates to serve you as examples of the lack of resources to address maintenance. I like the suggestion of local districts / agreements which could address these. (perhaps neighborhood-level performance parking revenue?)

3 - Do people leaning on trees hurt them that much? I could see younger saplings, but I think the mass of a mature tree isn't too bothered by a leaning person... or maybe I should start feeling guilty about all the times I've leaned on trees. Also... I've often wondered: is urine good for trees (water) or bad for trees (salts)?

4 - Issue might be mitigated somewhat if more bike racks are provided.

5 - The conventional government response would be to put up a sign saying "Caution: Trees", possibly with a little pictograph of roots pulling people down to the ground; and limbs reaching for people's heads. Though I mean this comment in jest, NPS' signing around the Tidal Basin is in that general league.

Though on a more serious note, this is a valid claim that might be addressed per #2. However, I'd also like to posit what of all the 1-2 ft tall fences people often trip on; or the boxes with no fences at all?

by Bossi on Jun 15, 2010 4:26 pm • linkreport

Improperly maintained tree grates can be devastating to the tree roots and the base of the trunk - permanently stunting that tree's growth. As Larchie notes, there are lot of conditions that need to be met before using tree grates - they should be an option of last resort. For the sake of the trees, people.

by Alex B. on Jun 15, 2010 5:07 pm • linkreport

I thought most tree grates these days allowed for some tree expansion. You should be able to easily take off an inner ring in order to make room for the tree to expand without having to change out a grate.

by Rose on Jun 15, 2010 5:08 pm • linkreport

Those shin-height fences look like they're designed to make a greater segment of the population applicable to ADA...

by andrew on Jun 15, 2010 5:19 pm • linkreport


Yes, they do allow for the tree to grow, but that's an issue of maintenance. Next time you're down on Pennsylvania Avenue by the FBI building, take a look at the tree grates that were never adjusted to the growing trees within them.

by Alex B. on Jun 15, 2010 5:37 pm • linkreport

I'm not clear why it is so terrible to lock a bike to a tree --

by Casey Anderson on Jun 15, 2010 5:41 pm • linkreport

There goes Alex again, caring about trees more than people.

I suspect it is bad for trees to lock bikes there because the thiefs cut down the trees to get to the bikes. You'd think with 20,000 cops in the city there would be enough police presence that guys with power tools might be afraid to work in the daytime....

by charlie on Jun 15, 2010 5:54 pm • linkreport

Are there really cases of people cutting down trees just to get at bikes? I mean, saplings are one thing... but I have a hard time picturing someone going through so much effort just for a bike. Unless it's a *really* nice bike, the wood itself would probably be worth more than the bike... and in that case, it'd be a wonder we have any trees at all.

by Bossi on Jun 15, 2010 6:08 pm • linkreport

@ Casey -- no, the chain or the lock, or even the bike itself, will chafe the bark and, when repeated by many people, is likely to wear the bark off entirely. Without bark the tree can't live, and even damaged bark compromises its ability to thrive.

Plus, people walking right around the tree will heavily compact the roots, preventing the soil from absorbing moisture and oxygen, both of which the tree needs.

by ah on Jun 15, 2010 8:00 pm • linkreport

Just to note that I witnessed a pedestrian slipping on the wet metal surface of a tree grate after a rain, 911 had to be called, it was not pretty.

And under no circumstances allow fences in tree boxes.

by Barry Childress on Jun 15, 2010 8:52 pm • linkreport

I too have seen the type of grate with removeable inner rings and thought those might work with minimal maintenance cost. Essentially anyone who saw the tree needing more room could remove the ring - could be a resident, or a merchant, or a passerby. Of course I guess people could steal the whole inner removeable ring area. Or all the leaves off the tree.

But the idea of planting in the parking lane sounds even better, if they are expanding the sidewalks on 18th to make more pedestrian space essentially then couldn't trees be moved into what was or still is part of the street?

What about installing some of that driveway-useable landscape material that lets grass grow through a metal screen? Traction problems, I guess.

As for attaching bikes to the tree trunks: could we get some sort of expandable rubber sheathing up to bike height, sort of a beaver-guard against bikers? In our neighborhood some of the water delivery systems (green baggies all around the tree - installed by Casey incidentally, I think) essentially block dogs from urinating on the trunk directly and dissuade people from attaching bikes or flyers directly to the bark. I don't know whether they also deflect the urine and/or function as a slow-trickle watering solution too... they are mysterious to me.

Larchie says he avoids recommending grates EXCEPT in circumstances exactly like those on a busy sidewalk in the circumstances that I think we expect to prevail in a busy pedestrian area with inadequate sidewalks to match the pedestrian volume of an area like Adams Morgan, no?

As for direction of the slots, couldn't something be designed with 1/2" round holes instead of slots, or some other method of perforation that would allow for seepage without posing a trip/trap/fall hazard?

I have seen folks ram their shins into the low-bar style tree boxes on Connecticut Ave right above Dupont Circle... amen to andrew for mentioning that.

And ah worries about compacting the roots. I thought some grates were designed like a post-and-beam system to transfer weight to limited points or to the periphery of the grate? Grates would have fewer people actually standing physically on the roots than happens with boxes now, I think.

In my neighborhood, the roots of mature trees planted years ago in (un-fenced, un-boxedm, un-grated) notches in the sidewalk at ground level have jacked up the sidewalks everywhere, which means they are not ADA compliant as they are. Our neighborhood recently had city contractors come through to re-pave several sidewalk sections to address that problem. Would either grates or boxes prevent the city from incurring that cost in the future?

On a philosophical level, walling off the trees from the people seems a bit like turning our street into a terrarium rather than bringing nature actually into contact with our daily lives. A bit like that fancy living room just for special company that my grandma had at her house - look but don't touch. Trees need care but we need people to care that they are there too. I realize the maintenance costs and concerns are real. Just wish we could make more trees work better in the city.

by Graham S on Jun 15, 2010 9:06 pm • linkreport

The problem with grates and the base of the trunk is that trees do not grow nice and pretty all the time, and even removing the rings in a grate won't prevent it from resting on the root structure.

On a philosophical level, walling off the trees from the people seems a bit like turning our street into a terrarium rather than bringing nature actually into contact with our daily lives. A bit like that fancy living room just for special company that my grandma had at her house - look but don't touch. Trees need care but we need people to care that they are there too. I realize the maintenance costs and concerns are real. Just wish we could make more trees work better in the city.

I can understand the objection, but far too many of the ideas to make trees work better in the city end up doing so at the expense of the tree's health.

And green baggies/donuts around tree trunks are indeed a slow watering solution.

As far as bikes go, this is a solution looking for a problem. The solution has nothing to do with trees at all - we need more bike racks.

by Alex B. on Jun 15, 2010 10:44 pm • linkreport

there are any number of bike racks that are designed to also act as tree guards - or should I say tree guards that double as bike racks?

In Baltimore all the tree grates are missing where I live, because they were all stolen to be sold for scrap metal.

by Lee on Jun 16, 2010 6:40 am • linkreport

Putting the trees in the parking lanes is a good idea. The trees can be put in bulb outs between every two or three parking spots. It barely costs space, it makes it very clear that there is parking, not an extra through lane, and is creates so much space on the sidewalk.

As I walk more and more through this area (NoVa and DC) I get more and more annoyed by all the clutter on side walks. Street lights, traffic signs, trees, magazine bins, uneven paving, missing pavement, overgrown bushes, it all narrows the side walk. So even where we had decent side walks, side walks are often only half the width in reality due to obstruction, creating bottle necks and dangerous situations when pedestrians are blocked and have to step in the roadway to avoid all the blockages. It gets worse when you walk on side walks that are also popular with bikers.

U St is a very good example of a side walk with plenty of interaction with buildings, but also with massive cluttering of the side walk.

Speaking of traffic signs on the side walk. Is there anybody that actually oversees who puts what signs where? Sometimes I feel there's just all these agencies that have authority to place street signs everywhere, and they do so, without any regard of whether the combined signage makes any sense. It would often even help if different signs were just stuck to a single pole.

by Jasper on Jun 16, 2010 9:57 am • linkreport

The Adams Morgan sidewalk widening is way overdue. Here are two drawings of the plans... from 2006!

by M.V. Jantzen on Jun 16, 2010 10:08 am • linkreport

The images that MV Jantzen links to are from an inactive ddot page. I saw a lot of different renderings in the planning stages but really have no idea what made it to the final plan. I would think they would release an up to date plan before breaking ground so residents know what to expect. Eitherway I am excited to have wider sidewalks. I will however miss the quirky, gritty, charm of Adams Morgan as it was. With Angled Parking and Stinky Gingkos. Still I dont know why they don't close the street to cars on the weekends. 18th would make a great pedestrian plaza.

by John on Jun 16, 2010 11:09 am • linkreport

@Jasper; "Putting the trees in the parking lanes is a good idea" Maybe. A lot of those parking lanes in high density areas are turned into rush hour lanes.

You forgot to list homeless people and unemployed young men as impediments to walking around on sidewalks. I'm not going to start on hispanics on bicycles. But yes, generally speaking, I think you point is spot on: too much stuff on sidewalks. In certain high density corridors there needs to be a clean-up.

There are sidewalks in NovA?

by charlie on Jun 16, 2010 11:30 am • linkreport

Without making any comment on the aesthetic benefits of tree grates, the ADA point seems to have merit.

ADA Accessibility Guideline (ADAAG) 4.5.4 specifies that grating on a walking surface may not have gaps exceeding 1/2 inch, which many tree grate styles may violate. (DC grates that pre-date the ADA might be grandfathered in, or they could be violations that DDOT hasn't gotten around to replacing, and no one has complained yet...) Tree grates are also more prone to up-thrust by growing roots, and the same 1/2 rule applies to vertical gaps - so over time a tree grate might be lifted and become "inaccessible" in teh ADA sense, even if it was accessible when installed.

Finally, a tree box is not discriminatory if it is universally inaccessible to all, so long as the accessible part of the sidewalk is otherwise ADA compliant.

by Anonymous Coward on Jun 16, 2010 2:37 pm • linkreport

BTW, I think those images were from, which now looks dead. Instead we have, but it doesn't have an archive of the old materials.

by M.V. Jantzen on Jun 16, 2010 4:23 pm • linkreport

I think the ideal solution to tree-box-vs-grates is to replicate what they did in Barracks Row, where the entire strip of space between the gutter and the sidewalk is left open for trees (with widely-spaced pavers). But you need a wide sidewalk for that.

For U St, that road needs to go on a diet and have a lane cut out in order to make the sidewalks managable, at least between 18th St and midway through the 1300 block.

by M.V. Jantzen on Jun 16, 2010 4:26 pm • linkreport

U St is a pretty major thoroughfare which gets packed every Thurs/Fri/Sat night... that could be a potential limitation in any discussions to reduce its capacity. On the other hand, it's also a pretty easy drive so long as you're not drive *toward* the bars at night; and sometimes left-turns can cause a bit of issue. Not that I'm against the thought; but it'd certainly take quite a bit of consideraiton.

I've often wondered if there'd be a better way to orient the myriad of stairs which occupy the lion's share of sidewalk space nearer to the Metro station. Awhile back I sketched up a bunch of potential treatments for realigning the stairs... a lot of them ended up merging 3 or 4 properties into a set of parallel stairs; or perhaps merging even more to form a more continuously covered two-story walkway. Both might be a bit out of context w/ the current streetscene; but not too far-fetched & heretical if any larger developments ever come through.

by Bossi on Jun 16, 2010 4:54 pm • linkreport

I've busted an ankle in one of the tree grates that does exist on 18th St. Not a pretty sight. But it was one with a square opening instead of a round opening, so perhaps I'd be slightly less accident-prone with a tree grate that dropped off in the same shape as the trunk. I do agree that, in certain parts of 18th St., the tree boxes, stairs, sidewalk seating, and crowds make pedestrian passage next to impossible. Yay for wider sidewalks!

by Mrs. D on Jun 19, 2010 6:09 pm • linkreport

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