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Re: No more roads...Where did you get your ramp meter dope, it's not entirely true...
Author: BOB2
Date: 06-14-2019 - 20:39
Gordy Wrote:
-------------------------------------------------------
> This past spring Washington Department of
> Transportation announced that it was going to
> begin
> installing metered on ramp devices on I-90 in the
> greater Spokane area to improve safety by slowing
> the flow of traffic. WSDOT stated that it no
> longer has a policy of adding capacity by adding
> lanes to freeways and will instead only meter the
> flow to improve safety but not capacity. Several
> Washington cities (including Spokane) have begun
> reducing lanes on major
> streets in what is called "traffic diets".
> Federal transit dollars pay for these programs
> (tied to federal funding for city bus systems)
> with the stated purpose of slowing traffic flow to
> encourage people to either walk, bike or ride city
> bus or light rail lines. Four or more lane
> streets are reduced to two lane streets with
> center turn lanes with islands in the center turn
> lanes at bus stops to prevent cars from passing
> stopped city buses. Justification for the traffic
> diets is safety, but accidents increase where
> lanes reduce (as people rush to get ahead of the
> line or beat the bus) and also increase where the
> streets return to 4-lanes as people hurry to pass
> any slow pokes or simply make up the lost time.
Gordy, I dunno where you got this interpretation of ramp metering being just about safety, because ramp metering is mostly done to maintain "capacity". Which in this case is a matter of the "fluid dynamics" of those non "compressible" flowing vehicles on a freeway lane. We use the measure of "vehicles per lane per hour", to determine the "flow rate".
Like all good rivers when they fill up, the flow rates on freeways can vary due to a number of conditions, even road "geography" like bends in a road can reduce the "flow rate" of vehicles passing through a curve (called strangely enough curve congestion...) where the traffic going around the curve, slows down to stop and go...
Ad, of course from our high school math, we know that a "stop" or when you car is a zero miles per hour, resulting in an "instantaneous "flow rate" of zero cars per lane per hour, for as long as that car is stopped.
One of the major causes of congestion on freeways is too many cars coming on and not enough getting off, leading to lane "saturation", and through put goes down to stop and go, and your optimal "flow rate" of 2000 cars per vehicle per lane at a nice smooth 55 or so, goes down to as low as 800 cars per lane per hour. We see this every day on the PeMS data flowing in from our freeway counters at "peaks" (and now all day on some routes) in LA. And thus, you've lost 60% of your potential "optimal" "throughput" capacity from traffic saturation of the lane.
Too many cars at one time trying to merge onto the freeway lanes, at the same time, is another major cause of "localized" traffic lane "saturation". Which disrupts flows and reduces throughput capacity, as too many vehicle are trying to merge into a flowing lane.
Ramp meters prevent all of those cars from trying to get on at the same time and disrupting the flow rate, and significantly increasing "flow rate" compared to uncontrolled merging without them. It does this by allowing a "mergeable" amount of traffic to enter the freeway, in small increments, that are less disruptive to the dynamic flow of the freeway. The math and science show that ramp metering is one of the most cost effective ways to prevent the loss of freeway "flow capacity"... It's not how many cars we can park on the freeway, it's how many we can "move"... And, wouldn't you rather be "moving"...?
Lane saturation and speed differential is the leading cause of collisions during peak periods on freeway, so ramp meters also do help to prevent accidents and improve "safety", and since accidents are the number one source of traffic congestion (avoidable travel time delay), that is a "two fer" "win-win" for both safety and once again "flow rate" capacity.
I was a choo-choo once upon a time, who likes choo-choo's, and has worked on choo-choo's projects, and the travel demand and economics of choo-choo projects. But, I'm also real good at highway cost benefit analysis, too.
Ramp meters are definitely the right thing to do, if you are having periods when you are approaching lane flow "saturation". However, at some point, the freeway is just plain full, and traffic flow breaks down, which is why you see "peak traffic times spreading" as folks leave earlier and later to avoid the "traffic" congestion, then folks will be forced to a0 drive to closer places, b) build alternatives to take the trips off, or c) add more lanes.
Ramp meters have a history of controversy. And, one Minnesota legislator from suburban Minneapolis hated them so much, he got legislation passed to make MinnDot to turn them off, to see what would happen, which caused massive gridlock, and this little political "stunt" was the experiment that showed proved just how well they worked.
Adding more lanes which become saturated, is 1)often very much more expensive and disruptive on an existing freeway, and 2) won't really add that much trip making capacity for the tax dollars spent, Which is why some rail projects, like the RCTC I-10 Coachella Valley rail service looks good on a "cost per additional rider" basis, compared to more freeway widening.
Now, you know why ramp meters work on freeway, and why a good case for rail can be made as a cost effective alternative, in some cases. Class is over, professor Bob is going to go eat, and watch a movie, now.....
-------------------------------------------------------
> This past spring Washington Department of
> Transportation announced that it was going to
> begin
> installing metered on ramp devices on I-90 in the
> greater Spokane area to improve safety by slowing
> the flow of traffic. WSDOT stated that it no
> longer has a policy of adding capacity by adding
> lanes to freeways and will instead only meter the
> flow to improve safety but not capacity. Several
> Washington cities (including Spokane) have begun
> reducing lanes on major
> streets in what is called "traffic diets".
> Federal transit dollars pay for these programs
> (tied to federal funding for city bus systems)
> with the stated purpose of slowing traffic flow to
> encourage people to either walk, bike or ride city
> bus or light rail lines. Four or more lane
> streets are reduced to two lane streets with
> center turn lanes with islands in the center turn
> lanes at bus stops to prevent cars from passing
> stopped city buses. Justification for the traffic
> diets is safety, but accidents increase where
> lanes reduce (as people rush to get ahead of the
> line or beat the bus) and also increase where the
> streets return to 4-lanes as people hurry to pass
> any slow pokes or simply make up the lost time.
Gordy, I dunno where you got this interpretation of ramp metering being just about safety, because ramp metering is mostly done to maintain "capacity". Which in this case is a matter of the "fluid dynamics" of those non "compressible" flowing vehicles on a freeway lane. We use the measure of "vehicles per lane per hour", to determine the "flow rate".
Like all good rivers when they fill up, the flow rates on freeways can vary due to a number of conditions, even road "geography" like bends in a road can reduce the "flow rate" of vehicles passing through a curve (called strangely enough curve congestion...) where the traffic going around the curve, slows down to stop and go...
Ad, of course from our high school math, we know that a "stop" or when you car is a zero miles per hour, resulting in an "instantaneous "flow rate" of zero cars per lane per hour, for as long as that car is stopped.
One of the major causes of congestion on freeways is too many cars coming on and not enough getting off, leading to lane "saturation", and through put goes down to stop and go, and your optimal "flow rate" of 2000 cars per vehicle per lane at a nice smooth 55 or so, goes down to as low as 800 cars per lane per hour. We see this every day on the PeMS data flowing in from our freeway counters at "peaks" (and now all day on some routes) in LA. And thus, you've lost 60% of your potential "optimal" "throughput" capacity from traffic saturation of the lane.
Too many cars at one time trying to merge onto the freeway lanes, at the same time, is another major cause of "localized" traffic lane "saturation". Which disrupts flows and reduces throughput capacity, as too many vehicle are trying to merge into a flowing lane.
Ramp meters prevent all of those cars from trying to get on at the same time and disrupting the flow rate, and significantly increasing "flow rate" compared to uncontrolled merging without them. It does this by allowing a "mergeable" amount of traffic to enter the freeway, in small increments, that are less disruptive to the dynamic flow of the freeway. The math and science show that ramp metering is one of the most cost effective ways to prevent the loss of freeway "flow capacity"... It's not how many cars we can park on the freeway, it's how many we can "move"... And, wouldn't you rather be "moving"...?
Lane saturation and speed differential is the leading cause of collisions during peak periods on freeway, so ramp meters also do help to prevent accidents and improve "safety", and since accidents are the number one source of traffic congestion (avoidable travel time delay), that is a "two fer" "win-win" for both safety and once again "flow rate" capacity.
I was a choo-choo once upon a time, who likes choo-choo's, and has worked on choo-choo's projects, and the travel demand and economics of choo-choo projects. But, I'm also real good at highway cost benefit analysis, too.
Ramp meters are definitely the right thing to do, if you are having periods when you are approaching lane flow "saturation". However, at some point, the freeway is just plain full, and traffic flow breaks down, which is why you see "peak traffic times spreading" as folks leave earlier and later to avoid the "traffic" congestion, then folks will be forced to a0 drive to closer places, b) build alternatives to take the trips off, or c) add more lanes.
Ramp meters have a history of controversy. And, one Minnesota legislator from suburban Minneapolis hated them so much, he got legislation passed to make MinnDot to turn them off, to see what would happen, which caused massive gridlock, and this little political "stunt" was the experiment that showed proved just how well they worked.
Adding more lanes which become saturated, is 1)often very much more expensive and disruptive on an existing freeway, and 2) won't really add that much trip making capacity for the tax dollars spent, Which is why some rail projects, like the RCTC I-10 Coachella Valley rail service looks good on a "cost per additional rider" basis, compared to more freeway widening.
Now, you know why ramp meters work on freeway, and why a good case for rail can be made as a cost effective alternative, in some cases. Class is over, professor Bob is going to go eat, and watch a movie, now.....
