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Comment by mlinksva | Hacker News Reader

I just became aware of the possibility of raised crosswalks, which seem like a fantastic idea -- no gradient for pedestrians, and a speed bump to slow cars -- https://sf.streetsblog.org/2018/05/22/walk-sf-campaigns-for-...

I imagine a raised crosswalk would also be more expensive than a curb cut. Are there any advantages or disadvantages relative to curb cuts for various disabilities?

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It's interesting how much of this is just about visual design. make it look like the cars have to cross the sidewalk rather that pedestrians crossing roads.

In fact, the ideas is thousands of years old. The ancient Romans had a concept of raised crosswalks in Pompeii:

> Blocks raised on the road allowed pedestrians to cross the street without having to step onto the road itself which doubled up as Pompeii's drainage and sewage disposal system. The spaces between the blocks allowed horse-drawn carts to pass along the road.

https://en.wikipedia.org/wiki/Pedestrian_crossing#History

That's awesome, thanks! Were raised crossing with spaces for cart wheels common around the world? Haven't cities everywhere had the sewage in the streets problem to varying extents for most of the time cities have existed?

Reykjavík has a few of those, but they are amazing. They are one of the few places where cars actually stop for pedestrians almost immediately (way more effective then simple painted crosswalk). They also do wonders in slowing down the traffic as it reaches downtown (way more effectively then simple speed bumps).

One objection to omnipresent speed bumps would be their effect on ambulances. Unless one were to outfit ambulances with those nifty active electromagnetic suspensions, so that you could actually speed to the hospital without slamming the patient into the ceiling...

In denser city environments where this would be installed, ambulances are already impeded in their speed and you likely wouldnt install this along a thoroughfare.

At typical E-series based ambulance as found in the US spend 50,000 miles bombing down potholed gravel roads before needing major service and that major service is more preventative than anything else.

People bouncing around inside and the ambulance box deteriorating are probably your first two limitations when it comes to ambulances driving fast over speed bumps.

Curb extensions are an alternative which may be more practical. Maybe that in combination with smart road humps[1] which respond to speed, would deter speeders down oak and feel streets in SF.

[1]https://hackaday.com/2017/08/14/smart-speed-bumps-slow-only-...

Curb extensions are awful for bicycles.

In my experience, crosswalks are counter-productive. They are typically placed in terrible locations, with poor lines of sight, or at otherwise busy and attention-demanding intersections. It is far safer to avoid the hell out of marked crosswalks, and cross the street in other locations, where you can clearly see the flow of traffic, and pick a slot to cross that is safe.

Unfortunately, the blind and visually impaired rely heavily on crosswalks to cross the road. Attempting to cross without the safety of a crosswalk will certainly result in death.

The problem is that mid-block crossing only works if traffic is slow and there are appropriate gaps in traffic. As an example, most of America lives in places that have streets that are eight to eleven lanes wide, with posted speed limits of 55-65 MPH and effective speed limits ten miles an hour above that. In the suburbs, crossing a busy road is essentially a death sentence, and coincidentally these are also the areas that are generally the most poorly equipped with crossing facilities.

Well yeah, you don't cross highways. Most streets are not 8-11 lanes wide, particularly in places where anyone would ever be walking along them. Places where pedestrians are common are in-town, low-speed (25-30 mph posted) streets.

The problem is we design our environments to be fundamentally hostile to walking between suburban neighborhoods, so only those who are desperate enough will walk. Usually this means the suburban poor, because cars can be prohibitively expensive.

This usually results in scenarios that beggar disbelief, like this one: https://www.huffingtonpost.com/radley-balko/raquel-nelson-ja...

>As an example, most of America lives in places that have streets that are eight to eleven lanes wide

Get out of your SF bubble. Not even the suburban sprawl in the south is built like that. You're exaggerating literally every detail you mentioned by a factor of two or more.

Two to four total lanes, with additional turn lanes at intersections is representative of the typical "suburban sprawl". You don't usually have to cross more than two lanes at a time because most places like that have raised medians. For non-major roads two lanes with occasionally a shared left turn lane is very common.

While I she agree that 8-11 is an exaggeration, it is easy to get up to 7: 1 right turn lane, 2 though lanes, 2 left turn lanes, and then 2 more through lanes in the opposite direction. Those aren't common in areas with lots of pedestrians, but I do see them all the time in other areas which do have cross walks (with traffic lights, if course) which I have seen used on occasion. Sometimes these even cross highways with 60 MPH (100 KPH) speed limits.

It's also not uncommon for major arterials to have shoulders, which are equivalent in crossing distance and safety to a road lane.

A couple of places in the South:

Atlanta: https://www.google.com/maps/place/Buford+Hwy+NE,+Georgia/@33...

Tampa: https://www.google.com/maps/place/Tampa,+FL/@27.9494221,-82....

Charlotte: https://www.google.com/maps/place/Charlotte,+NC/@35.2023214,...

Raleigh: https://www.google.com/maps/place/Charlotte,+NC/@35.7310989,...

Louisville: https://www.google.com/maps/place/Charlotte,+NC/@38.2154225,...

These are rather extreme examples (I said 8-11 based on my experiences in Long Island, NY), but things like this are not uncommon.

Most of these medians are basically nonexistent, and even if they did exist, there usually aren't any physical barriers that can stop a car above 50MPH, so they're just marginally safer than standing in the shoulders next to moving traffic.

> You don't usually have to cross more than two lanes at a time because most places like that have raised medians.

This can actually be a disadvantage, because in my experience, it has been rare where a crossing light on these types of roads gives you enough time to cross the entire road all at once, which can add a few minutes waiting for long, car-focused light cycles even for an able-bodied person. When crossing the street, the total distance and time it takes to go from one side to the other is what matters in terms of pedestrian comfort and convenience.

Speed tables have the side benefit of being fun for specific minority of vehicle drivers when pedestrians aren't using them.[1]

[1] http://image.fourwheeler.com/f/75606874+w660+h440+re0+cr1+ar...

Imagine making a right turn at an intersection where you have to cross two of these, one after the other. Your car's tires are not going to make nearly as good contact with the road, making your brakes less effective should you need to use them.

Turning, of course, puts lateral forces on the tires, making traction worse.

Sounds like a feature, not a bug - you'd better slow down quite a bit to make navigating that situation safe and make sure you aren't exceeding the safe speed for that intersection.

In the kind of dense urban areas where raised crosswalks have the most potential to make a difference in safety just by virtue of the raw number of people who use those street features, pretty much every improvement in some way contributes to lowering and moderating motor vehicle speed.

Tokyo is pretty darn dense and the normal, legal speed of traffic in most areas with crowded crosswalks exceeds speed bump speeds.

City and traffic planners are sure to be concerned with increased congestion and reduced road throughput by adding speed bumps to intersections that are already in the most congested spots..

I disagree that making it less safe to navigate intersections at currently observed speeds is a good way forward. I also believe that if speed reduction is a identified goal there are ways to accomplish this without making navigation at current speeds more dangerous; such as psychological speed bumps.

>pretty much every improvement in some way contributes to lowering and moderating motor vehicle speed.

Such as dedicated bike lanes that are divided from the rest of the road, raised sidewalks and other methods of traffic control that keep different classes of traffic from interacting? /s

If you were to do all crosswalks at an intersection like this, it's much more common to just raise the entire intersection as a massive speed table. https://nacto.org/publication/urban-street-design-guide/inte...

Pedestrians are able to negotiate gradients more easily than cars, so this seems inefficient.

The inefficiency for cars is a feature. It means drivers will slow down and thus kill less.

https://www.strongtowns.org/journal/2018/1/25/speed-kills-so...

Some pedestrians can manage a sloped curb at a crosswalk. Others may have a more difficult time of it.

By contrast, all cars must be able to drive up and down a short slope. They must do so to enter most parking lots, for instance, so performing a similar maneuver at an intersection is no big deal.

So many of our problems with regard to urbanism are rooted in making things efficient for cars over other users.

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