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Old 02-08-2015, 12:57 PM
 
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Here’s another example of good signal progression in metro Detroit. If a driver is able to maintain the speed limit, they should theoretically never get stopped at a red light regardless of what direction they are traveling. In order to achieve good signal progression for both directions of travel, traffic signals need to be spaced far enough apart. All too often, signals are spaced too closely together and achieving good dual progression becomes impossible (closely spaced signals kill good signal progression). In the case of Big Beaver Road, the signals (that stop both directions of travel) are spaced 1-mile apart.




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Old 02-08-2015, 01:00 PM
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Location: Long Island / NYC
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why would closely spaced signals kill good signal progression? Brooklyn avenues have a signal every block (a signal every mile seems impossible there!), but when traffic is low you can keep a green for a while, but eventually you lose it. Could the close spacing be a reason?
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Old 02-08-2015, 01:19 PM
 
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Originally Posted by nei View Post
why would closely spaced signals kill good signal progression? Brooklyn avenues have a signal every block (a signal every mile seems impossible there!), but when traffic is low you can keep a green for a while, but eventually you lose it. Could the close spacing be a reason?
There are essentially three main factors that effect signal progression: signal spacing, speed, and cycle length. A resonant cycle is a cycle length that achieves perfect two-way progression.

Below is a graph that shows the resonant cycle at varying signal spacing and speed limits:

While a resonant cycle is an ideal cycle to shoot for, it’s often not practical to achieve. As a real life example, consider Beach Boulevard near Long Beach, California. The corridor has a speed limit of 50 mph with major signals spaced roughly 2600 feet apart. Referring to the chart, a resonant cycle along Beach Boulevard would be achieved at a 70 second cycle. A 4-phase signal running a 70 second cycle would lead to a very high lost time (which is the amount of time dedicated to the yellow/all red safety clearances). Since a 70 second cycle length isn’t practical, there is no way to achieve a resonant cycle for Beach Boulevard (drivers will get stopped at red lights in at least one direction of travel, regardless of how well the signals are timed).

You can use the chart to determine the resonant cycle for any speed limit/signal spacing combination. The signals along Park Avenue in Manhattan are only spaced 260 feet apart and have a speed limit of 30 mph. Obviously, based on the chart, there is no way to get good dual-progression along this street. The signals would need to be spaced roughly 1,000 feet apart to achieve good dual progression (and then only if the corridor is running a 50 second cycle, which is extremely short).
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Old 02-08-2015, 01:35 PM
nei nei won $500 in our forum's Most Engaging Poster Contest - Thirteenth Edition (Jan-Feb 2015). 

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Location: Long Island / NYC
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a cycle length is the length of time a car driving at that speed will get a green for?
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Old 02-08-2015, 01:50 PM
 
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The cycle length is the amount of time it takes a traffic signal to sequence through all of its signal phases. A signal phase is essentially a turning movement.

As an example, assume a signal gives 40 seconds of green time for NB/SB traffic followed by 40 seconds of green time for EB/WB traffic. This would be referred to as a simple two-phase signal and the cycle length would be 80 seconds.
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Old 02-08-2015, 03:48 PM
 
Location: Portland, Oregon
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Originally Posted by impala096 View Post
Three miles in a minute is NASCAR speeds! You can travel roughly a minute per mile on select routes in metro Detroit. Did somebody else claim they could travel 3 miles in a minute? That's insane.

Most people assume that the big wide boulevards of the Motor City were built to cater to the automobile. The reality is much different. The transportation system of Detroit was originally centered around transit. The city had plans to construct rapid transit lines running underneath the major thoroughfares of the city and the Detroit Rapid Transit Commission (back in the 20's) concluded that 120 feet is the minimum street width that should be considered for a 4-track rapid transit line. Outside of the city limits, the ROW was expanded to 204 with 86 feet dedicated for surface rail lines. The wide streets of Detroit and the wide boulevards of the suburbs are a direct result of the region's vision to have a world class transit system. It just never materialized.
It is a shame that Detroit didn't follow through with this plan. They would be in a much better position today if they had.
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Old 02-08-2015, 05:33 PM
 
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A lot of highway bridges will include underbelly supports (sheets of plywood) to prevent dislodged chunks of concrete from falling onto unsuspecting motorists. Heck, there has been a couple of highway bridge collapses in recent months. America's highways are vastly underfunded, based on your very own determinant. Why focus on the crumbling transit infrastructure and make no mention of the crumbling highway infrastructure? More money needs to be spent on America's roads.
Infrastructure in general suffers from lack of investment. True there was some effort to address this after the US economic collapse, also to create some jobs. Today the unemployment problem has eased somewhat, but the infrastructure problem remains.
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Old 02-08-2015, 08:52 PM
 
Location: Vallejo
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Originally Posted by urbanlife78 View Post
It is a shame that Detroit didn't follow through with this plan. They would be in a much better position today if they had.
Or much worse.

Hard to call, honestly. A big problem Detroit has is too little population for its infrastructure. That's not a unique problem, Detroit is just the largest city that suffered it. Pittsburgh, Cleveland (both of which have rail transit) are right up there as well. It's by no means as simple as the presence of rail transit would have meant Detroit would look more like Chicago or Boston rather than like Cleveland. Of course, pretty much anywhere is better off than Detroit.
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Old 02-08-2015, 10:50 PM
 
Location: Portland, Oregon
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Originally Posted by Malloric View Post
Or much worse.

Hard to call, honestly. A big problem Detroit has is too little population for its infrastructure. That's not a unique problem, Detroit is just the largest city that suffered it. Pittsburgh, Cleveland (both of which have rail transit) are right up there as well. It's by no means as simple as the presence of rail transit would have meant Detroit would look more like Chicago or Boston rather than like Cleveland. Of course, pretty much anywhere is better off than Detroit.
Rail transit wouldn't be a singular saving grace for Detroit, but it would have been much easier to redevelop Detroit had it have it like it was planned. I doubt Detroit would have been any worse than it is today if it had rail transportation.
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Old 02-09-2015, 04:46 AM
 
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Originally Posted by impala096 View Post
I wonder what the percentages would be if you took NYC out of the equation.
How much I love driving my van
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