The answer is probably pretty obvious, but I figured I’d ask some folks who know for sure.
I live in the LA area, and all of our traffic signals are mounted to tall metal poles which arch over the street so that they’re placed in a readily-visible position for drivers, as seen here. However, having travelled recently Detroit, I noticed that all of the signals seemed to be hung by wire strewn above the streets where they could sway freely in the wind, such as here. It reminded me that I’ve been to other parts of the country where I’ve seen this (I think the last place I saw it was in the Reno/Tahoe area).
Is this done for weather-related reasons? Is it random preference? Or is it something else altogether?
In south Florida they are switching to big honkin metal structures that can withstand hurricane winds. After the last few hurricane seasons the wire hung streetlights were strewn all around the countryside and intersections were like playing Russian roulette.
The wire ones seem to work fine here in New England. The intersections are generally smaller and I don’t notice the lights out of alignment. And I’m sure it costs much less than those big poles, which are probably also a safety concern.
Would I be right in assuming these different kinds of signs are not actually manufactured by a government agency? If that’s the case, then it might just be a matter of there being a range of different traffic-signalling products available, perhaps manufactured by a number of competing companies, and that local traffic planners [del]get a bigger backhander[/del] prefer the products from one company or the other.
Telemark and Spin Gears are right, the signal head-on-a-wire is cheaper. As Mangetout guessed, signal heads are manufactured by private firms. Construction of the metal poles and masts is more expensive.
It probably has to do with when and where the signal was installed, as well. Traffic patterns and all that. For example, most of the major streets in my town have the signals mounted on metal poles. They’re sturdier, and more attractive in the downtown area.
The westernmost thoroughfare at the edge of town, (called, not surprisingly, Western Avenue) though, for years had just the single signals hanging from a wire across the middle of the intersection. Several intersections just had simple flashing red or yellow lights hung from wires. When those lights were installed, that area was heavily covered with orchards that came right up to the street corners in many places. Orchardists probably didn’t like the idea of the city/county installing bigass metal light poles in their orchards, likely requiring removing trees, and so the signals were simply strung between the existing power poles. Also, because most of the traffic on Western Avenue was just agricultural vehicles and the cars of the few people who lived up there, there was little justification for the expense of fancier traffic signal setups.
As the city grew and traffic became congested downtown, the city decided that it would be good to try to route some of that traffic onto little-traveled Western Avenue. By this time, most of those old orchards had been sold and torn out to build houses. Realizing that those simple old traffic signals would be inadequate, they were replaced with the complex signals mounted on metal poles, as part of the same project that widened Western Avenue.
As to why a city would still have the old-fashioned lights-on-a-wire in busy downtown areas, it makes sense that traffic patterns in that city are such that shutting down an intersection to install new light poles is simply infeasible. So they make do with what they’ve got. Installing those big poles frequently involves completely replacing the sidewalks around the intersection, as the old sidewalk doesn’t provide an adequate foundation for those big poles. This can cause accessibility problems for businesses located on those corners, and they complain …
Oh boy, a chance to pick on Texas! Texas hangs on wires and by pole… but horizontally. (I think NM might do same thing.)
I always thought this was dumb because what if you were red/green colorblind and you came from anywhere outside of Texas? You wouldn’t know which light you should go through until you got used to it.
Besides that, we have standards for a purpose people! There is no use to be different just to be different when safety and traffic is involved.
There are ways around that. There’s a busy 4-lane road near here that recently had its remaining wire-hung lights replaced. The poles were sunk away from the corners, off the sidewalk, and were most likely wired late at night. The only real probelm the crews encountered was at one corner where they had to remove a retaining wall, dig into a hill, and put in a new wall.
It’s not that weird. With one exception–which I think doesn’t exist anymore–red is always on top and green is always on the bottom; in the case of Texas they’re just rotated 90° counterclockwise.
There are generally horizontal lights but there is also often a vertical set as well. Las Cruces pretty much uses all poles, so does Albuquerque, Santa Fe, and probably most of the other larger towns. Anyway, in Albuquerque, almost every light is pole-mounted, generally a combination of horizontally mounted lights on one pole that extends over the traffic lanes and a vertical mount that’s in the the median on a seperate pole. Sometimes, depending on road design and traffic patterns, there are extra lights. Anyway, the only exception I can think of is one fairly large intersection in the NE section of town (Wyoming and Menaul, for anyone familiar with the area) that still has the lights just hanging from wires.
Now that I think about it, yeah, I think everywhere in this state will use horizontal lights. Personally, it never really struck me as odd.
Not just South Florida, and not at all intersections. The vast majority of our intersections still have them mounted on wires attached to four concrete poles at each corner, but the major intersections are switching to the monotubes you mentioned earlier. Most of them are a dark brown, but one of them in my lovely town was painted baby blue. There was a vote, you see, and that’s the color the people voted for.
If you click here and scroll down, you can see a small picture of one of them being installed. This is the intersection where the tube is now blue. After this one went up, those four concrete poles came down.
As to the number of signal heads, the rule is (or was a couple years ago when I worked at the City): one for each lane of travel plus one extra (set lower on the main pole) for pedestrians.
just for clarity I’ll add:
The two poles on opposite corners with a wire spanning the intersection on the diagonal is called a Diagonal Span (duh)
The one with four poles (typically) on each corner with spans running directly from one pole to the next at right angles is called a Box Span
Some are aligned like a Box only the span wire runs a short distance towards the center of the intersection were it supports a box configuration not directly leading from each pole. This one is called a Bullring or Suspended Box and is used at very wide intersections to overcome the problem were the vehicles stop too far from the nearest signal indication
Earlier some have mentioned the vertical pole (Stanchion) with a roughly horizontal or arched pole (Cantilever) and these are called Mastarms.
Lastly, there is the MonoTube type as shown in the soon-to-be-blue picture. These are typically the most costly of all those mentioned.
As stated earlier, the decision of which to use depends on many design criteria and as stated before, the costs increase with each “upgrade” to the type selected.
As to kickbacks; after designing many, many signals I am still waiting on a check years later.
