Installing traffic signals at a intersection

[Tom89t]

If you were install traffic signals at a intersection, which design would you choose?

[Brandon]

If you were install traffic signals at a intersection, which design would you choose?

Anything that involves using a permitted left or banning left turns and making them go to the U-Turn area (Michigan Left) and turning right.  There is never any reason for a protected-only left, IMHO.

[realjd]

If you were install traffic signals at a intersection, which design would you choose?

Anything that involves using a permitted left or banning left turns and making them go to the U-Turn area (Michigan Left) and turning right.  There is never any reason for a protected-only left, IMHO.

A double or triple left at a high traffic intersection still isn't a reason for protected only? A Michigan left doesn't have the throughput for that amount of traffic, and permissive lefts can be dangerous at that wide of an intersection due to poor sight lines.

[Brandon]

If you were install traffic signals at a intersection, which design would you choose?

Anything that involves using a permitted left or banning left turns and making them go to the U-Turn area (Michigan Left) and turning right.  There is never any reason for a protected-only left, IMHO.

A double or triple left at a high traffic intersection still isn't a reason for protected only? A Michigan left doesn't have the throughput for that amount of traffic, and permissive lefts can be dangerous at that wide of an intersection due to poor sight lines.

If you need a triple left, then it is time to think differently for the volume of traffic.  And, yes, Michigan Lefts and other channelization handle the volume quite well.  Take a drive down Telegraph or Eight Mile sometime.

[tradephoric]

US 19 through Pinellas County in Florida has long had the dubious distinction of being one of the most dangerous roads in America especially for pedestrians.  This section of road is a good case study on how not to design safe and efficient intersections. 

This is a typical intersection along US 19 (US 19 & 118th taken in 2007):


The intersection has since been grade separated and this is what it looks like today:


Even with the new design pedestrians crosswalks are 190 feet long and cross 9-lanes of traffic.  At 3.5 ft/sec, that's over 60 seconds of walk and flashing don't walk time for the through movement just to satisfy the ped times. 

There are many other intersections along US-19 that are similar to the first picture and try to squeeze capacity by simply adding more left turn lanes (there's even a triple left-turn lane at US19 & Old Bailey's Bluff Rd).  Regardless of how short you can get those lefts to run, a 4-phased signal with dedicated lefts won't be able to achieve the same capacity as a simple 2-phased signal.

Here's an example of a Michigan Left Turn design in Troy Michigan where two 6-lane boulevards intersect (Coolidge & Big Beaver):


With this design, the median acts as a pedestrian refuge similar to splitter islands within a roundabout making crossing the intersection much safer.

[roadfro]

Anything that involves using a permitted left or banning left turns and making them go to the U-Turn area (Michigan Left) and turning right.  There is never any reason for a protected-only left, IMHO.

A double or triple left at a high traffic intersection still isn't a reason for protected only? A Michigan left doesn't have the throughput for that amount of traffic, and permissive lefts can be dangerous at that wide of an intersection due to poor sight lines.

If you need a triple left, then it is time to think differently for the volume of traffic.  And, yes, Michigan Lefts and other channelization handle the volume quite well.  Take a drive down Telegraph or Eight Mile sometime.

But sometimes the triple left is really the only solution. For example, I've lost count of how many triple lefts are located along the Las Vegas Strip...there's no available right of way for Michigan Lefts or any other channelization there.

[tradephoric]

A little off topic but this is the list of the 10 most dangerous cities for pedestrians according to an ABC news article:
The Worst Cities for Pedestrians

1. Orlando/Kissimmee, Florida
2. Tampa/St. Petersburg/Clearwater, Florida
3. Jacksonville, Florida
4. Miami/Fort Lauderdale/Pompano, Florida
5. Riverside/San Bernardino/Ontario, California
6. Las Vegas/Paradise, Nevada
7. Memphis, Tennessee
8. Phoenix/Mesa/Scottsdale, Arizona
9. Houston/Sugar Land/Baytown, Texas
10. Dallas/Fort Worth/Arlington, Texas

Here's an example of some sidewalk running next to US-23,a pretty major route through the city of Jacksonville:

If you look on Google, sidewalk runs right along the road from US-1 to I-95.  Not only that the pedestrians get to navigate a few lamp posts in the middle of the sidewalk while walking down the street.

EDIT:  Ok, this is more on topic then i first thought.  Take a look at the new overpass design at US 19 & 118th.  Notice how the sidewalk runs right next to the road?  I know ROW is a bitch to acquire but this road is notorious for pedestrian fatalities.  It would have been nice to see at least a 10-15 foot buffer between the sidewalk and the edge line of the road.

[roadman65]

Anything that involves using a permitted left or banning left turns and making them go to the U-Turn area (Michigan Left) and turning right.  There is never any reason for a protected-only left, IMHO.

A double or triple left at a high traffic intersection still isn't a reason for protected only? A Michigan left doesn't have the throughput for that amount of traffic, and permissive lefts can be dangerous at that wide of an intersection due to poor sight lines.

If you need a triple left, then it is time to think differently for the volume of traffic.  And, yes, Michigan Lefts and other channelization handle the volume quite well.  Take a drive down Telegraph or Eight Mile sometime.

But sometimes the triple left is really the only solution. For example, I've lost count of how many triple lefts are located along the Las Vegas Strip...there's no available right of way for Michigan Lefts or any other channelization there.

For triple left turn lanes there should be separate greens for each way like many major roads in New Jersey intersecting state highways.  It allows one direction to make all movements at one time and then does the same for the other side.  There are some places in Florida that have separate greens especially in Orlando.  Only two places I know of that have triple left turn lanes.  One is on the ramp from Exit 272 on the Florida Turnpike to turn left onto SR 50 at Oakland, FL.

[roadman65]

I actually like mast arms as supposed to span wires, but one thing I heard from someone that works in a local signal repair unit that mast arms cannot be used a large intersections.  However, we all know that is untrue as there are many intersections out there that have mast arms that are wide in dimensions.  We can be grateful though that this prevented FDOT from installing an ugly truss assembly in Orlando at Orange Blossom Trail and Sand Lake Road like many other streets on OBT as part of a widening program that was supposed to " clean up" the Orange Blossom Trail although it never worked out.  Ugly green trusses are at many Orange Blossom Trail intersections from Florida Mall to Oak Ridge Road that wasted tax payers money as someone in Orlando convinced many Orange County residents that it would improve the area as it already has a bad reputation.

I have seen some intersections in Florida where two side by side span wires are used instead of one.  On John Young Parkway at the I-4 Eastbound off ramp there are two side by side diagonal assemblies that are not needed.  Then around Universal you have an "X" configuration with two diagonal wires meeting in the middle.  This, I was told, was for hurricane force winds as it would not sway as much do to both wires holding each other back! 

Bottom line is CalTrans has many large intersections with mast arms and New Jersey would mount arms from the median if necessary if the side ones will not reach.  I think that Florida is reluctant to change and would look for any excuse to keep their traditional span wire assembly between two concrete strain poles.  It was only since the mid 90's when you seen local agencies (in Florida all signals are operated either by county or municipality) start the trend as before that span wire assemblies were being used exclusively.

I just think mast arms are nicer looking than span wire assemblies.  Its just me, although the span assembly does work better at shallow angle intersections I have to admit no argument there.

[DaBigE]

I actually like mast arms as supposed to span wires, but one thing I heard from someone that works in a local signal repair unit that mast arms cannot be used a large intersections.  However, we all know that is untrue as there are many intersections out there that have mast arms that are wide in dimensions.

Agreed.  Although, "large intersections" can be quite an ambiguous statement.  Up in Wisconsin, WisDOT has standard details for signals with a monotube up to 55-ft in length, which is enough to usually cover 4-5 travel lanes.  I've heard rumors that up to 70-ft monotube designs are in the works.  One also has to remember that these massive signal poles also require large foundations, so maybe the area your signal repair person works in has some tight space limitations.

I just think mast arms are nicer looking than span wire assemblies.  Its just me, although the span assembly does work better at shallow angle intersections I have to admit no argument there.

Also agreed.  This is one reason I am sad to see Wisconsin's overhead signal designs change.  (Thanks to the MUTCD---topic for the other thread.)  IMHO, hoizontally-mounted signals in a trombone arm look so much cleaner and "finished" than their vertically-mounted cousins.  Wisconsin examples: https://www.aaroads.com/forum/index.php?topic=5016.25

[Ian]

I have no preference over span wires and mast arms as to which is better. I've always liked the span wires since I'm so used to seeing them scattered throughout the Northeast.

[florida]

Ugly green trusses are at many Orange Blossom Trail intersections from Florida Mall to Oak Ridge Road that wasted tax payers money as someone in Orlando convinced many Orange County residents that it would improve the area as it already has a bad reputation.

And those ugly green trusses replaced quite a few old-style signals along that stretch.

I prefer span wires to mast arms. Mast arms seem so boring unless they're huge monolithic structures

[roadfro]

I actually like mast arms as supposed to span wires, but one thing I heard from someone that works in a local signal repair unit that mast arms cannot be used a large intersections.  However, we all know that is untrue as there are many intersections out there that have mast arms that are wide in dimensions. 

You'd have to define "large". Nevada has many wide intersections using a single mast arm for traffic signals. I think the longest standard size mast arm is in the neighborhood of about 65 or 70 feet. There some longer ones, but these use specially-designed support poles more --at these points, they tend to try to use an additional median installation for the turning traffic if possible.

StreetView example or Tropicana Avenue EB at Las Vegas Blvd, Las Vegas, NV - accommodates 4 thru lanes and 2 left turn lanes, so closer to 70 feet assuming standard 12-foot lane widths.

I just think mast arms are nicer looking than span wire assemblies.  Its just me, although the span assembly does work better at shallow angle intersections I have to admit no argument there.

There's always another option in these situations... Nevada has made limited use of monotube assemblies at shallow angle intersections in order to get the layout of a span wire with the look and structure of a mast arm.

StreetView example of an older shallow-angle monotube assembly, on Las Vegas Blvd & Craig Rd/Nellis AFB main gate in North Las Vegas, NV. (Newer installations use thicker tubes.)