Thursday, September 29, 2011

Sharing Space

In the past I've (blasély) talked about naked streets, or as they are more euphemistically known, shared space, mostly in the context of other work, such as understanding street hierarchies. Now I would like to offer a few suggestions on realizing shared space:

1. The essence of shared space is that the travel ways (carriageways or cartways) are shared between all modes. Very narrow streets in older cities are often naturally shared spaces.
2. The lone useful metric of success in measuring fully shared space is whether or not walking in the middle of the road feels comfortable and natural; this is because of pedestrians' tendency to favor sidewalks wherever feasible; when pedestrians can effectively lay a territorial claim to the middle of the road, the motorist's response must be to accommodate to the pedestrians' territory, rather than pedestrians being excluded from motorists' territory. The pragmatic application of this is that shared space forces a natural speed limit, for motorized transport, in the range of 15 mph or 20 kph. In other words, sharing space naturally caps design speed.

This is the theory. Not rocket science, is it? Now to some application guidelines.

3. There is a clear hierarchy of streets even within the shared space paradigm; this hierarchy manifests as the distinction between residential and commercial shared spaces. This is in part because commercial shared space can be a bit more forgiving than residential.

Let us now elaborate the design guidelines for what both types have in common.

4. The street is narrow to very narrow. In most North American settings, this narrowness can be accentuated with onstreet parking.
5. The street is unidirectional (one-way).
6. Buildings alongside shared spaces are close together and cluster on, or close to, the lot line.

Now, let's get on to what describes a residential shared space.

7. There is little, if any, differentiation between carriageway and non-carriageway on shared-space streets. A small "sidewalk" may still be allowable as a space for street furniture (such as stoops, benches, trash cans, or street trees), but this space should not extend further than 3 feet from the lot line: pedestrians will still favor sidewalks when the sidewalk is as narrow as 5 feet.
8. The street is rarely more than  35 feet wide, and is, indeed, frequently less.
9. There is almost always only one travel lane; this travel lane is usually 10 feet wide when it accommodates automobile traffic.
10. The street must be quiet, that is, with an AADT under 500.
11. Parking lane(s) can be provided on either side of the travel lane: shared spaces can thus vary in width from sub-10-foot (very rare) to about 35 feet (fairly rare). Because the cars are parked close to the lot line, there is little comfort space for pedestrians there, bringing them out into the middle of the road. Onstreet parking is often an excellent way to artificially narrow a road.
12. Residential shared spaces tend to break into three typologies: the 10-foot class, with only one lane and no onstreet parking; the 20-foot class, with one travel lane and one parking lane, and finally the 30-foot class, with one travel lane and a parking lane on either side.

Commercial shared spaces are a bit different.

13. Commercial shared space is different from residential primarily due to the presence of storefronts facing the street.
14. Where there is shared space with a parking lane and commercial facing one side of the street, the parking lane always goes on the other side.
15. Commercial shared  space can have deeper sidewalks: up to 10 feet, due to the importance of window-shopping in commerce. This is especially true where there is parking on both sides of the all-mode travel lane.
16. It may be the case that commercial shared space can handle multiple travel lanes (no more than two). However, if this is so, the travel lanes still must be unidirectional if side-by-side, and bidirectional if and only if the parking lane is provided between travel lanes, and that if there are two travel lanes, then there must be direct access from the sidewalk to the travel area on at least one side (i.e. no parking lane).
17. This necessarily means that commercial shared space can be no more than 50 feet wide in most cases, with the possibility of 60 foot in the extreme case of having two parking lanes sandwiched between the travel lanes.
18. Through-traffic not wishing to use the commercial street needs to have a bypass easily available. This is particularly important since space sharing in popular commercial areas is likely to massively depress AADT along that particular road.

From this discussion, I would like to suggest that good 30-foot typologies would be (a) storefront-sidewalk-travel-sidewalk-storefront or (b) storefront-sidewalk-all mode travel-onstreet parking-lot line (non-storefront); 40-foot, (a) storefront-sidewalk-travel-travel-sidewalk-storefront or (b) storefront-sidewalk-travel-parking-sidewalk-storefront; and 50-foot, (a) storefront-sidewalk-travel-travel-parking-sidewalk-storefront, (b) storefront-sidewalk-travel-parking-travel-sidewalk-storefront, or (c) storefront-sidewalk-parking-travel-parking-sidewalk-storefront. Commercial streets narrower than 30 ft. can also, of course, occur; indeed, at the narrowest widths, they would be busier versions of residential shared space. Madrid's Calle de Preciados is one such example.

Delineating shared space is my next topic. Of course, the best way would be by use of a concept I call materials assonance, where particular materials are used to define how such-and-such part of so-and-so street is supposed to behave. Belgian blocks, for example, could define parking areas, while brickwork defines through passages, and slate, areas where street furniture goes. But implementation of a materials assonance plan would take quite some time, and would likely be undercut by state DOTs' insistence on confusing streets with roads. In the interim, before materials-assonance plans can be tried out, I would suggest a simple paint sheme:
Sharrows are already being used to identify spaces shared by bikes and cars. If the sharrows itself is what is used to identify shared space, then why not take the concept one step further and use it to define where pedestrians have right-of-way as much as cars? Furthermore, bike shared space is included in pedestrian shared space, so this sharrows is even more general than the bike sharrows. Painting pedestrian sharrows at the entrances to shared-space networks would territorialize the interior of the network for the pedestrian, and over time, lay the ground work for areas to develop materials assonance schemes in.


  1. As soon as there are cars parked on one side, a "shared space" street become much less walkable, and starts to feel like a place for cars. I can't imagine that a street with parking on both sides could feel like a good place to walk down the middle. The commercial space example, with 10 foot sidewalks and parking on both sides of a travel lane, might be fine for bikes, but people walking would certainly stay on the sidewalks. That's not shared space.

    In general, a street where pedestrians feel very comfortable will be somewhat uncomfortable for bikes, and very uncomfortable for cars. If a bike rider feels they can ride thru at 15 mph (this is my usual cruising speed on a bike), people walking will constantly need to be on their guard. And if cars are traveling that fast... well, I'm not going to let my 3 year old walk with me down that street.

  2. This is true to a certain extent...but when you don't have naturally narrow streets to work with, there really aren't too many practicable solutions. The big trick is I want people to start asking how do we make streets we already have more for people and less for cars? Sometimes it's not the answers that are important: it's the question.