Denver Ramp Meters

[Mark68]

OK...I've wondered about this for a while, and it's kind of a pet peeve of mine.

I grew up in Southern California and was a kid when ramp meters became commonplace out there. Usually, if there are two-lane onramps controlled by ramp meters, the meters alternate to let one lane of traffic proceed at once. It seems intuitive to me.

But CDOT seems very counter-intuitive. They install meters on two-lane ramps that turn green simultaneously, with the ramp narrowing to one lane almost immediately. Why? This just seems stupid. It causes the two cars that are side-by-side to race each other to jockey for position on the one lane that continues, which, IMO, makes it much more likely that some type of sideswipe would ensue.

[Milepost61]

I heard a long time ago second or third hand that there was someone at CDOT that read somewhere the meters are able to operate at slightly higher capacity if you do the simultaneous greens rather than the ping-ponging back and forth. Don't know if any of that is true or not though.

[US 89]

I heard a long time ago second or third hand that there was someone at CDOT that read somewhere the meters are able to operate at slightly higher capacity if you do the simultaneous greens rather than the ping-ponging back and forth. Don't know if any of that is true or not though.

Isn't the point of a meter to reduce the amount of traffic entering the freeway? Why would you want to increase the capacity of the meter?

[roadfro]

I heard a long time ago second or third hand that there was someone at CDOT that read somewhere the meters are able to operate at slightly higher capacity if you do the simultaneous greens rather than the ping-ponging back and forth. Don't know if any of that is true or not though.

Isn't the point of a meter to reduce the amount of traffic entering the freeway? Why would you want to increase the capacity of the meter?

A ramp meter isn't meant to reduce incoming flow, but rather "meter" it so that it's a steady stream of vehicles merging instead an alternating cycle of big platoons and random arrivals.

I can't speak to whether simultaneous or staggered release ramp meters are more efficient. But I'd think that for a 2-Lane ramp that staggered release would be better. Could be they have old controllers or equipment that doesn't accommodate staggered release...

[Elm]

It sounds like recent CDOT answers to the question have been along the lines of "that's the way it's always been here, and it'd cost a lot to change it."

In this older answer, they mention a financial factor; apparently they'd have to use overhead signals to be allowed to alternate lanes. In a more recent answer here (first question of a series), they talk more about the technology and plans for being more adaptive.

[MNHighwayMan]

In this older answer, they mention a financial factor; apparently they'd have to use overhead signals to be allowed to alternate lanes.

I think they are mistaken about needing overhead signals. MnDOT has always done alternating ramp meters, and they are all side-mounted.

Edit: They are not mistaken. Here is the relevant section from the MUTCD.

If more than one lane is present on an entrance ramp and the ramp control signals are operated such that green signal indications are not always displayed simultaneously to all of the lanes on the ramp, then one signal face shall be provided over the approximate center of each separately-controlled lane.

However, I checked the Minnesota version of the MUTCD, and that paragraph is slightly different.

If multiple lanes are present on an entrance ramp and the ramp control faces are operated such that green signal indications are not always displayed simultaneously to all of the lanes on the ramp, then:

A. If there are two separately-controlled lanes, a minimum of two signal faces shall be provided for each of the two lanes, with both mounted at the side of the roadway on a single pole (see Option below), or a combination thereof.

B. If there are three or more separately-controlled lanes, one signal face shall be provided over the approximate center of each separately-controlled lane.

That's why MnDOT gets away with side-mounted ramp meters. I guess my post isn't really relevant anymore, but I'll leave this up because it's still interesting.

[roadfro]

^ I think MnDOT has the right idea here. I've always found it weird that the MUTCD allows a single signal head per lane for ramp meters and there's no redundancy.

During the I-80 rebuild circa 2009, Nevada DOT installed temporary ramp meters in Reno on the two-lane EB ramp at Virginia, and used side mount poles (with one low and one higher signal head per lane). The permanent ramp meters installed a year or two later are overhead with one signal head per lane. Always thought it was a bit of a regression.

[MNHighwayMan]

^ I think MnDOT has the right idea here. I've always found it weird that the MUTCD allows a single signal head per lane for ramp meters and there's no redundancy.

Agreed. If they're going to mandate the overhead signal, then I'd think you'd want to have a second side-mounted one too.

But unless you have an on-ramp with more than two lanes (and where does such a thing exist?) why are overheads necessary? For two lanes, I would think side-mount is more than sufficient.

[US 89]

^ I think MnDOT has the right idea here. I've always found it weird that the MUTCD allows a single signal head per lane for ramp meters and there's no redundancy.

During the I-80 rebuild circa 2009, Nevada DOT installed temporary ramp meters in Reno on the two-lane EB ramp at Virginia, and used side mount poles (with one low and one higher signal head per lane). The permanent ramp meters installed a year or two later are overhead with one signal head per lane. Always thought it was a bit of a regression.

The one-lane ramp standard in Utah is a redundant side signal. For two-lane ramps, there is generally one overhead signal for each lane, plus a signal on the side, like this or this. However, in some cases where they've upgraded a 2-section meter to a 3-section, they got rid of the side signal. That didn't make much sense to me.

But unless you have an on-ramp with more than two lanes (and where does such a thing exist?) why are overheads necessary? For two lanes, I would think side-mount is more than sufficient.

How about right here? There are quite a few 3-lane ramps in this area.

[MNHighwayMan]

But unless you have an on-ramp with more than two lanes (and where does such a thing exist?) why are overheads necessary? For two lanes, I would think side-mount is more than sufficient.

How about right here? There are quite a few 3-lane ramps in this area.

That's a new one to me. All the metered ramps in the Twin Cities are at most two lanes.

[jakeroot]

But unless you have an on-ramp with more than two lanes (and where does such a thing exist?) why are overheads necessary? For two lanes, I would think side-mount is more than sufficient.

I absolutely agree, although that's difficult with HOV bypass lanes, as are common in Seattle.

WSDOT always used side-mounted two-head-per-lane meter signals, but has now switched to overhead-only for two- and three-lane meters (single lane meters continue using pole-mounted signals). Back in the day, before they started using overhead signals, they actually built bulb-outs at ramp meters to accommodate the pole-mounted signal when there was also an HOV bypass lane. They no longer do interesting things like this.

During the I-80 rebuild circa 2009, Nevada DOT installed temporary ramp meters in Reno on the two-lane EB ramp at Virginia, and used side mount poles (with one low and one higher signal head per lane). The permanent ramp meters installed a year or two later are overhead with one signal head per lane. Always thought it was a bit of a regression.

Also agree with this. Ramp meters are unusual in that they completely disobey basic MUTCD rules: more than one color of orb per approach, having only one signal for each/all movements, etc. Yes, there's an exception to these rules for ramp meters, but those rules aren't, nor weren't, for nothing. Ramp meters really need a special design, probably something that utilizes pole-mounted signals (making it harder to see the other lanes' signals, for example). Triple lane ramp meters would need a special design, maybe more akin to a tollbooth setup.

Of course, the old adage goes, "if it ain't broke, don't fix it" ... while we could say that overhead-only ramp meters are working fine, we also know that ramp meters came after basic rules for signal redundancy, so one could say that, in some states, ramp meter design is, in fact, "broke".

[jakeroot]

WSDOT did a study on I-90 near Spokane, and in it, they studied installing ramp meters (the first in Eastern Washington).

Part of the study looked at the operational capacities of each style of meter (the image below is a snippet from pgs 15 & 17 of this PDF).

(on the second table, the Browne (Division) meter would be the first in Washington to operate with dual-car release (all meters in Western Washington stagger releases)).

[MNHighwayMan]

But unless you have an on-ramp with more than two lanes (and where does such a thing exist?) why are overheads necessary? For two lanes, I would think side-mount is more than sufficient.

I absolutely agree, although that's difficult with HOV bypass lanes, as are common in Seattle.

It really only requires a narrow island to separate. Here's one example on I-35W in Minneapolis, and another, older example from the NB MN-65 ramp to EB US-10.

[jakeroot]

But unless you have an on-ramp with more than two lanes (and where does such a thing exist?) why are overheads necessary? For two lanes, I would think side-mount is more than sufficient.

I absolutely agree, although that's difficult with HOV bypass lanes, as are common in Seattle.

It really only requires a narrow island to separate. Here's one example on I-35W in Minneapolis, and another, older example from the NB MN-65 ramp to EB US-10.

For sure. Those appear very similar to my Seattle example. But if you're looking to quickly set up a meter, building a curb large enough to fit both the signal and a neutral area around it to prevent it being hit by trucks, can take longer than just throwing something overhead. Far be it for me to suggest that laziness is in any way acceptable, but I can certainly understand why a DOT might go the overhead-only route in this case (or at least, overhead only on the side closest to the HOV lane), since building that curbing is quite a bit more engineering than just installing some detectors in the ground and putting some signals up.

[Mark68]

It seems like CDOT might be slowly adding overhead meters to supplement side mounts, at least on new construction. They recently reconstructed the interchange at I-25 & Santa Fe (US 85) and the ramps do have the overhead supp meters. However, they're still operating in tandem.

https://goo.gl/maps/s9SYUvGgvKv

https://goo.gl/maps/RtJzPPbSsb62

[US 89]

But unless you have an on-ramp with more than two lanes (and where does such a thing exist?) why are overheads necessary? For two lanes, I would think side-mount is more than sufficient.

How about right here? There are quite a few 3-lane ramps in this area.

That's a new one to me. All the metered ramps in the Twin Cities are at most two lanes.

After looking bit further in detail, there is one four-lane metered ramp that I'd forgotten about. It's on the ramp to northbound I-15 from 9000 South.

Ramp meters really need a special design, probably something that utilizes pole-mounted signals (making it harder to see the other lanes' signals, for example).

Now that you mention it, the earliest overhead ramp meters in the Salt Lake area actually used 3M PV signals, such as these and these (both have since been replaced). I'm fairly certain the 500 South ramp also had 3Ms at one point, but GSV doesn't have anything old enough.

[jakeroot]

Ramp meters really need a special design, probably something that utilizes pole-mounted signals (making it harder to see the other lanes' signals, for example).

Now that you mention it, the earliest overhead ramp meters in the Salt Lake area actually used 3M PV signals, such as these and these (both have since been replaced). I'm fairly certain the 500 South ramp also had 3Ms at one point, but GSV doesn't have anything old enough.

The new signals at the US-89 ramp use the [briefly-manufactured] Intelight Electronic Steerable Beam (ESB) signals, so they're still using limited-visibility signals to some extent. Good to see some thought being given to the possibility of confusion.

Here's a thread on them: https://www.aaroads.com/forum/index.php?topic=21172.0

[US 89]

Ramp meters really need a special design, probably something that utilizes pole-mounted signals (making it harder to see the other lanes' signals, for example).

Now that you mention it, the earliest overhead ramp meters in the Salt Lake area actually used 3M PV signals, such as these and these (both have since been replaced). I'm fairly certain the 500 South ramp also had 3Ms at one point, but GSV doesn't have anything old enough.

The new signals at the US-89 ramp use the [briefly-manufactured] Intelight Electronic Steerable Beam (ESB) signals, so they're still using limited-visibility signals to some extent. Good to see some thought being given to the possibility of confusion.

Here's a thread on them: https://www.aaroads.com/forum/index.php?topic=21172.0

Holy crap. How have I been going through there for years and never noticed that? You learn something new every day, I guess. That may well be the only location in the entire state with those signals - I can't find a single other ramp meter with them. The vast majority of PVs now are the newer McCain variety, and there are a couple 3Ms left in Salt Lake City.

I imagine the reason they installed these at that location was to avoid conflict with the US 89 northbound through lane, which doesn't merge onto I-15. Although the PV aspect doesn't seem to work in my experience, as well as this imagery from 2015...

[MNHighwayMan]

I imagine the reason they installed these at that location was to avoid conflict with the US 89 northbound through lane, which doesn't merge onto I-15. Although the PV aspect doesn't seem to work per this imagery from 2015...

Newer imagery from 2018 seems to indicate that the beams were adjusted.

Edit: Or they were dark? Hard to tell.

[US 89]

I imagine the reason they installed these at that location was to avoid conflict with the US 89 northbound through lane, which doesn't merge onto I-15. Although the PV aspect doesn't seem to work per this imagery from 2015...

Newer imagery from 2018 seems to indicate that the beams were adjusted.

Eh, the meters were probably off at that time; these ones only run during afternoon rush hour, and that's a morning GSV based on the position of the sun (and lack of heavy traffic on either 89 or 15).

[jakeroot]

Ramp meters really need a special design, probably something that utilizes pole-mounted signals (making it harder to see the other lanes' signals, for example).

Now that you mention it, the earliest overhead ramp meters in the Salt Lake area actually used 3M PV signals, such as these and these (both have since been replaced). I'm fairly certain the 500 South ramp also had 3Ms at one point, but GSV doesn't have anything old enough.

The new signals at the US-89 ramp use the [briefly-manufactured] Intelight Electronic Steerable Beam (ESB) signals, so they're still using limited-visibility signals to some extent. Good to see some thought being given to the possibility of confusion.

Here's a thread on them: https://www.aaroads.com/forum/index.php?topic=21172.0

Holy crap. How have I been going through there for years and never noticed that? You learn something new every day, I guess. That may well be the only location in the entire state with those signals - I can't find a single other ramp meter with them. The vast majority of PVs now are the newer McCain variety, and there are a couple 3Ms left in Salt Lake City.

I imagine the reason they installed these at that location was to avoid conflict with the US 89 northbound through lane, which doesn't merge onto I-15. Although the PV aspect doesn't seem to work per this imagery from 2015...

They're a very rare signal to begin with. I only know of a handful of installs near me. And I've certainly never seem them in Canada.

Their effectiveness (or lack thereof) is something I've also noticed. I don't know why this is. I've seen some that work extremely well, but I've seen others that don't seem to have any PV-features enabled at all.

[Elm]

It seems like CDOT might be slowly adding overhead meters to supplement side mounts, at least on new construction. They recently reconstructed the interchange at I-25 & Santa Fe (US 85) and the ramps do have the overhead supp meters. However, they're still operating in tandem.

https://goo.gl/maps/s9SYUvGgvKv

https://goo.gl/maps/RtJzPPbSsb62

I drove down C-470 for the first time in a month or so and saw some more recent additions of this sort of ramp meter, for northbound at Alameda Pkwy, southbound at Morrison Rd, and one of Ken Caryl Ave (northbound, I think); they had "˜one per green each lane' like I-25 & Santa Fe. Judging by this page, there are more coming or that I didn't notice in the area.

CDOT a few more ramp metering projects going on I-25 south of Denver, too, in Douglas County (Plum Creek to Lincoln) and Colorado Springs (mostly Bijou to N Nevada). If they've finished any, I haven't seen them–I'm curious what style they'll go with.