Cloverleafs: Make CD lanes yield to loop traffic

[sprjus4]

Normal people don't expect to have to stop or yield while on an Interstate.

I've heard people refer to arterial roads that are 4-lane divided highways with spread out traffic signals, and even go through some towns that serve mainly long-distance traffic as interstates.

The term has been spread culturally to essentially any long-distance road, whether it has intersections, signals, or even passes thru towns as an "interstate".

I've even heard some people refer as a 2-lane long distance road as an "interstate".

[Scott5114]

Oklahoma DOT actually tried exactly this at the I-35/I-240 interchange in the late 90s. The C/D road traffic displayed a strong preference for crashing into cars from the ramps rather than yielding. No amount of orange flags on the yield and yield ahead signs corrected this behavior (and let me tell you the orange flag industry in Oklahoma had to have had a literal banner year while this was going on), so they had to change it back after everyone in central Oklahoma made fun of ODOT for not knowing how to set up proper traffic control on a cloverleaf.

[SectorZ]

Do c/d lanes without cloverleafs have to yield to ramp traffic? If so, you're making an inconsistent design for these ramps, and inconsistent experiences among the same types of ramp systems will lead to more consistent accidents.

[kphoger]

How anyone can say with a straight face that these do not look like a wide-open highway is beyond me.

CD roads are clearly part of the interchange. Interchange ramps are not part of the interstate mainline and nobody expects the ramp to have same priority as the mainline.

No, it isn't necessarily clear that C/D roads are part of the interchange.  Especially at large system interchanges with C/D roads that might even serve more than one exit, the C/D road can function as a second part of the highway.

While you're correct in asserting that people don't expect the ramp to have the same priority as the mainline, that's an argument against yourself.  Nobody expects traffic from the loop on-ramp to have as much priority as traffic that's on the C/D mainline, and yet think it won't be any problem at all to have the mainline yield to the ramp.

the yield signs are basically pointless there, as the on-ramp forms an added accel/decel lane.

I think drivers of top heavy and underpowered commercial vehicles would disagree. So do taxpayers who benefit from cost savings of cloverleafs built smaller.

Which part would they disagree with?  The fact that the on-ramp forms an added accel/decal lane?  How do these drivers feel about similar interchanges that don't use any yield signs at all, such as ones I've already posted?

Taxpayers benefit from interchanges that aren't cloverleaves.

Oklahoma DOT actually tried exactly this at the I-35/I-240 interchange in the late 90s. The C/D road traffic displayed a strong preference for crashing into cars from the ramps rather than yielding. No amount of orange flags on the yield and yield ahead signs corrected this behavior (and let me tell you the orange flag industry in Oklahoma had to have had a literal banner year while this was going on), so they had to change it back after everyone in central Oklahoma made fun of ODOT for not knowing how to set up proper traffic control on a cloverleaf.

Oh, you mean common sense happened?

[Scott5114]

Oklahoma DOT actually tried exactly this at the I-35/I-240 interchange in the late 90s. The C/D road traffic displayed a strong preference for crashing into cars from the ramps rather than yielding. No amount of orange flags on the yield and yield ahead signs corrected this behavior (and let me tell you the orange flag industry in Oklahoma had to have had a literal banner year while this was going on), so they had to change it back after everyone in central Oklahoma made fun of ODOT for not knowing how to set up proper traffic control on a cloverleaf.

Oh, you mean common sense happened?

Naturally. Point being that if your cool new road idea was once used as instance of an ODOT Special, maybe you need to reconsider whether it's really a cool idea or not...

[yand]

Oklahoma DOT actually tried exactly this at the I-35/I-240 interchange in the late 90s. The C/D road traffic displayed a strong preference for crashing into cars from the ramps rather than yielding. No amount of orange flags on the yield and yield ahead signs corrected this behavior (and let me tell you the orange flag industry in Oklahoma had to have had a literal banner year while this was going on), so they had to change it back after everyone in central Oklahoma made fun of ODOT for not knowing how to set up proper traffic control on a cloverleaf.

The late 90s was a long time ago, many things are different now. I'm certainly interested in the data for how this arrangement has impacted the San Antonio Loop 1604/I-10 interchange. Maybe 20+ years has not changed a thing and the same epidemic of crashes are occurring in Texas at this very moment.

No, it isn't necessarily clear that C/D roads are part of the interchange.  Especially at large system interchanges with C/D roads that might even serve more than one exit, the C/D road can function as a second part of the highway.

I already addressed this. Cloverleaf exclusive CD lanes and Local Lanes are both called CD lanes, but obviously not the same thing. One is a ramp built exclusively to facilitate left turning movements without disturbing the mainline, the other facilitates travelling between any combination of the express lane access points and numerous local exits/entrances.

While you're correct in asserting that people don't expect the ramp to have the same priority as the mainline, that's an argument against yourself.  Nobody expects traffic from the loop on-ramp to have as much priority as traffic that's on the C/D mainline, and yet think it won't be any problem at all to have the mainline yield to the ramp.

Exiting traffic behaves differently from mainline traffic. Turns out if you intend to take the loop, you're much more open to slowing down and working with traffic already in the loop. Changing the yield sign just reinforces this behavior.

How anyone can say with a straight face that these do not look like a wide-open highway is beyond me.

Nah. This looks like a slightly enlarged 1 lane road with no breakdown lane, no passing lane, multiple incoming on ramps, and is about to end and merge onto the wide open highway next to it very soon.

[sprjus4]

The late 90s was a long time ago, many things are different now.

No it's not, and no they aren't.

Exiting traffic behaves differently from mainline traffic. Turns out if you intend to take the loop, you're much more open to slowing down and working with traffic already in the loop. Changing the yield sign just reinforces this behavior.

I can say first hand I don't slow -way- down far before the ramp to exit unless it's congested. I'll ride up at full speed, and decrease speed once on the deceleration ramp and begin taking the turn.

Nah. This looks like a slightly enlarged 1 lane road with no breakdown lane, no passing lane, multiple incoming on ramps, and is about to end and merge onto the wide open highway next to it very soon.

It looks like a wide-open highway. I'm not going to crawl 25 - 30 mph on that lane. In free-flowing conditions, I'd ride up at 55 - 65 mph until passing the merge if somebody was not already entering at slow speed, then decrease, enter the deceleration lane, then slow down before and on the loop.

[yand]

Exiting traffic behaves differently from mainline traffic. Turns out if you intend to take the loop, you're much more open to slowing down and working with traffic already in the loop. Changing the yield sign just reinforces this behavior.

I can say first hand I don't slow -way- down far before the ramp to exit unless it's congested. I'll ride up at full speed, and decrease speed once on the deceleration ramp and begin taking the turn.

Nah. This looks like a slightly enlarged 1 lane road with no breakdown lane, no passing lane, multiple incoming on ramps, and is about to end and merge onto the wide open highway next to it very soon.

It looks like a wide-open highway. I'm not going to crawl 25 - 30 mph on that lane. In free-flowing conditions, I'd ride up at 55 - 65 mph until passing the merge if somebody was not already entering at slow speed, then decrease, enter the deceleration lane, then slow down before and on the loop.

The behavior you described is compatible with a yield sign and advisory speed on the CD lane.

[kphoger]

I'm certainly interested in the data for how this arrangement has impacted the San Antonio Loop 1604/I-10 interchange.

My suspicion is that the placement of the yield sign hasn't had much effect on driver behavior at all, but I too am interested to know if anyone has more information.  Here in Wichita, at the 54/135 turban interchange, where ramps converge to form one lane such as here, the placement of the yield sign has near-zero effect on how people merge:  they simply take turns.  In fact, more people tend to ignore the placement of the yield sign (instead simply assuming that traffic on the right should merge into traffic on the left) than heed it.  FYI, this is a merge point that I use daily, so my personal anecdotal perspective on trending driver behavior there actually does mean something.

Changing the yield sign just reinforces this behavior.

As I've already stated, and as other members have already corroborated, changing the yield sign does little to change actual driver behavior.  The geometry of the highway affects driver behavior much more.

[MikeTheActuary]

It looks like a wide-open highway. I'm not going to crawl 25 - 30 mph on that lane. In free-flowing conditions, I'd ride up at 55 - 65 mph until passing the merge if somebody was not already entering at slow speed, then decrease, enter the deceleration lane, then slow down before and on the loop.

I'm rather fond of the tactic taken with the C/D lanes I've encountered in the Montréal area, where the C/D lane gets a discrete posted (but usually ignored) speed limit.
For example: https://www.google.com/maps/@45.3806692,-73.5185478,3a,75y,167.36h,103.76t/data=!3m6!1e1!3m4!1sSFqlX9SUJbLlxfhBX9sqgA!2e0!7i16384!8i8192

[renegade]

Personally, I cannot recall the last time I saw a yield sign at an on-ramp anywhere. 

I will pray I am never on the same highway as the OP, and that if I am, they better have the best insurance.

[kphoger]

Personally, I cannot recall the last time I saw a yield sign at an on-ramp anywhere. 

I will pray I am never on the same highway as the OP, and that if I am, they better have the best insurance.

Having yield signs at on-ramps or not is generally a state-by-state thing.  The OP must be from a state where they're common.

[Brandon]

Naturally. Point being that if your cool new road idea was once used as instance of an ODOT Special, maybe you need to reconsider whether it's really a cool idea or not...

This has got to be the quote of the month, and we're only 3 days into it. 

[Brandon]

Personally, I cannot recall the last time I saw a yield sign at an on-ramp anywhere. 

I will pray I am never on the same highway as the OP, and that if I am, they better have the best insurance.

Having yield signs at on-ramps or not is generally a state-by-state thing.  The OP must be from a state where they're common.

They're not used much in Illinois, Indiana, Ohio, Wisconsin, or Michigan.  Iowa used to use them, but I'm not so sure anymore.

[kphoger]

Yeah, a lot of states don't even use them at all.

[CtrlAltDel]

How anyone can say with a straight face that these do not look like a wide-open highway is beyond me.

I have no opinion on the loop-ramp-yielding question, but I have to say that neither of these pictures looks like a wide-open highway. They both look like ramps to me, mostly because there is only one lane and because there is a bigger highway right next to them.

[ErmineNotyours]

Offramp yielding happened naturally at the eastbound George Washington Parkway to northbound I-395 ramp just outside of Washington DC.  This is a cloverleaf off a mainline, not a C/D, but I was following traffic to let SB I-395 to EB Geo Washington pass through until there was a big enough gap in front of me to accelerate and then decelerate into it.  Worse, it was backed up because traffic was cutting the line straight to my ramp, and I needed to go to the bathroom, and every delay was several more seconds of pain.



Example of an anti-CD abuse sign.

[US 89]

Offramp yielding happened naturally at the eastbound George Washington Parkway to northbound I-395 ramp just outside of Washington DC.  This is a cloverleaf off a mainline, not a C/D, but I was following traffic to let SB I-395 to EB Geo Washington pass through until there was a big enough gap in front of me to accelerate and then decelerate into it.  Worse, it was backed up because traffic was cutting the line straight to my ramp, and I needed to go to the bathroom, and every delay was several more seconds of pain.

Funny you mention this: the last time I was in DC, I took a taxi from the city to DCA and passed through that exact same interchange. Despite the presence of a yield sign on the loop ramp from the northbound GW Parkway, the driver came to a full stop in the right lane of I-395 to let all the loop traffic in. We sat there for probably around 30 seconds, until he decided there was a big enough gap between cars to gun it into exit 10B.

[jakeroot]

Offramp yielding happened naturally at the eastbound George Washington Parkway to northbound I-395 ramp just outside of Washington DC.  This is a cloverleaf off a mainline, not a C/D, but I was following traffic to let SB I-395 to EB Geo Washington pass through until there was a big enough gap in front of me to accelerate and then decelerate into it.  Worse, it was backed up because traffic was cutting the line straight to my ramp, and I needed to go to the bathroom, and every delay was several more seconds of pain.

Funny you mention this: the last time I was in DC, I took a taxi from the city to DCA and passed through that exact same interchange. Despite the presence of a yield sign on the loop ramp from the northbound GW Parkway, the driver came to a full stop in the right lane of I-395 to let all the loop traffic in. We sat there for probably around 30 seconds, until he decided there was a big enough gap between cars to gun it into exit 10B.

When I'm in DC (and on the few occasions where I'm not on the metro), I usually pass right through this spot, although usually in the left lane so as to exit onto 14th. Merging in the DMV is a concept that they don't seem to fully grasp.

I've heard people refer to arterial roads that are 4-lane divided highways with spread out traffic signals, and even go through some towns that serve mainly long-distance traffic as interstates.

The term has been spread culturally to essentially any long-distance road, whether it has intersections, signals, or even passes thru towns as an "interstate".

I've even heard some people refer as a 2-lane long distance road as an "interstate".

This definitely varies by region. In Seattle, the term "interstate" is virtually unheard of. You're either very specific (e.g. "Interstate 5") or you just say "freeway". Non-freeway roads are usually referred to by their specific name; sometimes, "highway".