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Thread: City blocks, what is too big?

  1. #1

    City blocks, what is too big?

    I've been reading Jane Jacob's book "The Death and Life of Great American Cities" for several months now (off and on) and I've been wondering what she means by blocks that are too large/long. How large is too large? Our Downtown has blocks about 230ft x 440ft, and the urban neighborhoods just outside our Downtown that have about 30 houses per block (no front yards or just a few feet between them, but have back yards) and are about 280ft x 620ft or longer. (and these are areas that have become slums and have the highest crime rates of the city, and are home to the gangs and drug dealing)

    How large is too large for street safety and urban diversity?

    Also, she talks about large cities, etc... However I don't know how big is medium, large etc... Since she talk about cities like Boston and NYC. My city is 400,000-500,000 people in a metro of about 2 million.

  2. #2
    Cyburbian Luca's avatar
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    I have actually been taking pictures of 'short blocks' in London (they ar ecomapratively rare, oddly enough) and they definitely tend to produce an impalpable sense of human sclae / well-being.

    Without any sicentific evidence but simnply as an avid citywalker, etc., I would say that, in a grid, anything longer than 150-200 yards without a break in two directions begisn to rreally influence you wlakign opportunities and longer than 500M feels like a rat run.

    OBVIOUSLY, iof the street itself is mangificent/fascinating, you may happily wlak along if for miles, but I tend to fidn that theshorter blocks work better..

    Sorry if thsi looks very basic/cobbled together, gotta run
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  3. #3
    As with all things in this business, there is no universal "metric" to apply. What is pleasant and comfortable depends on your personal experiences.

    However, if it takes more than 5 minutes to walk around the block, it's probably too big.

  4. #4
    Cyburbian Jeff's avatar
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    If in a place with public water, I like to think of it as a function of overlapping fire hydrants. If the req. is for a hydrant every 700' I like 1200' for the max block length. This way you can serve the entire block (both sides of street) with a hydrant on each corner.

    I dont think there is a right answer to this though.

  5. #5
    Cyburbian AubieTurtle's avatar
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    I don't know what the perfect block length is but I do know if they get too big, it causes jaywalkers because of the long distance required to go all the way down to the intersection to cross the street when what you want to get to is straight across the street from you. With a short block, the person is more likely to obey the law and not risk crossing midblock.

    You can always put in a midblock crossing but those aren't very popular with drivers and I suspect they're less safe than intersection crossings because drivers just don't notice them.
    As democracy is perfected, the office of president represents, more and more closely, the inner soul of the people. On some great and glorious day the plain folks of the land will reach their heart's desire at last and the White House will be adorned by a downright moron. - H.L. Mencken

  6. #6
    Cyburbian Plus
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    Quote Originally posted by Jeff View post
    If in a place with public water, I like to think of it as a function of overlapping fire hydrants. If the req. is for a hydrant every 700' I like 1200' for the max block length. This way you can serve the entire block (both sides of street) with a hydrant on each corner.

    I dont think there is a right answer to this though.
    For further discussion about hydrants, go to the ISO website:
    http://www.isomitigation.com/ppc/3000/ppc3010.html
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  7. #7
         
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    I agree that there is no magic number for block length. In some communities an 800 foot block may be too long if the common or customary standard is 400 feet.

    Where I have a problem is in existing urban grid systems when streets are vacated to accommodate large redevelopment projects. The customary street and sidewalk system is interrupted with T-intersections. This causes traffic and activity to concentrate on some streets and stop using others because of the inconvenience of driving or walking around the obstacle (or stop walking altogether). This, of course, has been a major issue with a lot of large urban renewal projects over the decades.

  8. #8
    In our grid system, we have 300-400' blocks. These work well for traffic control, as every other intersection requires vehicles to stop (Minus the thru collector streets), so from a traffic standpoint it works well at these lengths, as it keeps speeds from building, by limiting the space between stops to 600-800'.
    Who's gonna re-invent the wheel today?

  9. #9
    Cyburbian jmello's avatar
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    The blocks in our downtown grid are between 350-425' long. That is from centerline to centerline.

  10. #10
    Cyburbian DetroitPlanner's avatar
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    A typical Detroit Neighborhood is about six or seven blocks per mile (North South) by about 12 or 13 blocks (East-West). Streets have about 100-200 foot ROWs; depending upon functional class with some arterials being even wider.

    All of this goes out the window in the areas platted when ribbon farms ruled (From 1701 to the introduction of the State Plane system).

    Some blocks are significantly longer than others. For example, I could make it around my block in about 5 minutes-8 minutes, but my grandmother lives on the block south of me, and it would take a good 15 minutes to make it around her block.
    We hope for better things; it will arise from the ashes - Fr Gabriel Richard 1805

  11. #11
    Cyburbian Luca's avatar
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    Isn't it itnerestign taht msot peopel said soemthign like "there is no hard and fast rule2 but taht msot idnciate 100-150 meters (give or take)?

    I think that, liek so many aspects of architecture and urabnism, in fact there is more of a 'rule' than many realize.

    One mroe thing: BLocks tend to be rectangular, so when I said that I tend to find a certain size congenial, I eman the long side. the short side can be sa nrrow as 3-4 'lots', as far as I'm concerned.

    Certainly, if Iw as palnnigna town from scratch, or rehabilitating a greyfield/brownfield site I would go for smallish blocks.
    Life and death of great pattern languages

  12. #12
    Cyburbian AubieTurtle's avatar
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    Quote Originally posted by Luca View post
    Isn't it itnerestign taht msot peopel said soemthign like "there is no hard and fast rule2 but taht msot idnciate 100-150 meters (give or take)?

    I think that, liek so many aspects of architecture and urabnism, in fact there is more of a 'rule' than many realize.

    One mroe thing: BLocks tend to be rectangular, so when I said that I tend to find a certain size congenial, I eman the long side. the short side can be sa nrrow as 3-4 'lots', as far as I'm concerned.

    Certainly, if Iw as palnnigna town from scratch, or rehabilitating a greyfield/brownfield site I would go for smallish blocks.
    Spent a little too much time on the block with the pubs tonight?
    As democracy is perfected, the office of president represents, more and more closely, the inner soul of the people. On some great and glorious day the plain folks of the land will reach their heart's desire at last and the White House will be adorned by a downright moron. - H.L. Mencken

  13. #13
    Cyburbian Tobinn's avatar
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    Block Length

    I could have sworn that Jacobs provided some typical, preferred block lengths in her book. I read it some time ago (also on an off for months) so I could be mistaken.

    Otherwise, I tend to agree that a good block length is between 350 and 600 feet.

  14. #14
    Cyburbian bocian's avatar
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    600' is tooooo long -- 200 to 300' is perfect in grid-based layouts. The issue here is that most American lots / houses are very wide and thus long blocks are necessary -- or you'd have 3 or 4 houses per weird short 300' blocks -- -- my Philly rowhouse was 14' wide, and we had 14 of them on our ~ 200' long block. The scale was nearly perfect.

  15. #15
    Cyburbian michaelskis's avatar
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    Quote Originally posted by jaws View post
    As with all things in this business, there is no universal "metric" to apply. What is pleasant and comfortable depends on your personal experiences.

    However, if it takes more than 5 minutes to walk around the block, it's probably too big.
    I agree, 5 minutes to get around a block is too long, and that it is all dependant on the setting. A block of buildings in NYC will be much different than a block of buildings in Sun Prairie Wisconsin.
    Quote Originally posted by DetroitPlanner View post
    A typical Detroit Neighborhood is about six or seven blocks per mile (North South) by about 12 or 13 blocks (East-West). Streets have about 100-200 foot ROWs; depending upon functional class with some arterials being even wider.

    All of this goes out the window in the areas platted when ribbon farms ruled (From 1701 to the introduction of the State Plane system).

    Some blocks are significantly longer than others. For example, I could make it around my block in about 5 minutes-8 minutes, but my grandmother lives on the block south of me, and it would take a good 15 minutes to make it around her block.
    One thing that is nice is arcades or alley ways in the block to provide a pedestrian cut through. I have noticed several redevelopment projects that have opened a section of the ground floor level to create small covered malls as people cut from one side of the block to the other. Each of the businesses inside still would have an exterior entrance and exit, but it does help during harsh weather to get from one shop to another.
    Not my monkey, not my circus. - Old Polish Proverb

  16. #16
    Cyburbian DetroitPlanner's avatar
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    Mike, I am talking about residential blocks. Interesting that you bring this up. Around here, more retail intense areas blocks are much smaller, and in industrial areas they can be a mile or longer!
    We hope for better things; it will arise from the ashes - Fr Gabriel Richard 1805

  17. #17
    Cyburbian michaelskis's avatar
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    Quote Originally posted by DetroitPlanner View post
    Mike, I am talking about residential blocks. Interesting that you bring this up. Around here, more retail intense areas blocks are much smaller, and in industrial areas they can be a mile or longer!
    Residential Blocks... Oh your right, in Detroit some of them are massive. I for the most part, I like the scale of the blocks in Downtown Detroit. We have a few in residental Grand Rapids that people will avoid just because it is like the great wall of houses.

    Industrial blocks are their own zip code! There is one occupied by a major pharmaceutical company (in the community that I work for) that to walk around the bock, it is just over 4 miles.
    Not my monkey, not my circus. - Old Polish Proverb

  18. #18
    On the extreme tight end, downtown Portland has 200' blocks, which were originally designed for maximum real estate values through corner retail visibility. Most communities I've looked at require less than ~600-800'. Of course, infrastructure costs rise generally with shorter block lengths. Everything's based on a football field in America, right?

  19. #19
    I think it depends, and is very context sensitive. I don't think any of the block sizes you mention are "too big" (the high crime in the longer block neighborhood probably is NOT due to the bllock length). The main thing is just to keep it at a pedestrian scale, and make it so the block can identify as a community of sorts.

    When J.J. talks about large blocks, I imagine she had in mind the Robert Moses redevelopments in New York, which involved "superblocks." For example, there's Stuyvesant Town and some typical 50s projects on the upper west side.

  20. #20
    I just happen to have read through a part of JJ's Death and Life that was about short blocks. She was saying that on long blocks, where people can't easily cut over to another, they will wind up taking the same route up and down their own long block to get where they need to go in their daily routine, rather than exploring and supporting business on other blocks that may be close as the crow flies but not in walking distance. And I think that here, yes, she is talking about diversity, mixing people into areas they don't necessarily need to go and maybe might not go, at least not regularly, if they have to go all the way around that long block to get there.

  21. #21
    Cyburbian DetroitPlanner's avatar
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    The size of a block does not indicate criminal activity. However, the lack of police sure would lead to an increase in criminals.

    Not everything involved with a well run City is due to the orderlyness of its geography. Adminstration and attitude mean a lot.
    We hope for better things; it will arise from the ashes - Fr Gabriel Richard 1805

  22. #22
    Cyburbian cdub's avatar
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    Agreed in that it does depend on the context (ie, industrial). A rule of thumb I've seen recently is a block perimeter of 1,320 ft, which gives you flexibility in block sizes. The 1,320' is based on a 5 minute walk and I don't think a 5 min. walk around the block is too much. Also think of it as walking in a linear direction for 4 blocks. Seems about right.

    A recent edition of the New Urban News publication had a tech section on the block and showed how you could accommodate parking in the block center with varying block sizes, all staying within the 1200 - 1320'.

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