The "Father of the DDI" Defends Left Hand Exit and Entrance Ramps

[kernals12]

There's space to put ramps on the outside of a freeway. It's much harder to put ramps on the inside.

Most rural freeways have wide medians

FTFY. I cannot think of a single urban freeway in either the Salt Lake or Atlanta area (the two metros I frequent most) with big enough medians to fit new left-exit ramps in.

I-93 has a good sized median north of Boston.

[hotdogPi]

There's space to put ramps on the outside of a freeway. It's much harder to put ramps on the inside.

Most rural freeways have wide medians

FTFY. I cannot think of a single urban freeway in either the Salt Lake or Atlanta area (the two metros I frequent most) with big enough medians to fit new left-exit ramps in.

I-93 has a good sized median north of Boston.

I'm not seeing anything near wide enough to put a ramp until you get into New Hampshire, with the exception of a short segment just north of MA 125 that doesn't have any cross streets to interchange with.

[kernals12]

There's space to put ramps on the outside of a freeway. It's much harder to put ramps on the inside.

Most rural freeways have wide medians

FTFY. I cannot think of a single urban freeway in either the Salt Lake or Atlanta area (the two metros I frequent most) with big enough medians to fit new left-exit ramps in.

I-93 has a good sized median north of Boston.

I'm not seeing anything near wide enough to put a ramp until you get into New Hampshire, with the exception of a short segment just north of MA 125 that doesn't have any cross streets to interchange with.

The most common reason for using left hand ramps is to reduce ROW requirements. A combined northbound exit and southbound entrance ramp will take up less space than if they used separate ones.

[interstatefan990]

The "median" on most urban freeways I drive usually amounts to a tall concrete barrier.

On some stretches of freeway where I drive, it's literally just a guardrail.

[jeffandnicole]

Well, understand that highways are built with ramp locations in mind.  You are all looking at *existing* highways that don't have space in the median for ramps.  Build a new highway from scratch, and you could much more easily design it with ramps in the median, vs on the right.

[1995hoo]

Well, understand that highways are built with ramp locations in mind.  You are all looking at *existing* highways that don't have space in the median for ramps.  Build a new highway from scratch, and you could much more easily design it with ramps in the median, vs on the right.

Or modify a highway, for that matter. The I-495 HO/T lanes in Virginia use almost entirely left-side ramps, with a few exceptions in the Tysons Corner area. That was a case of an existing road that generally had no median being rebuilt into a wider road that still has no median but has the express lanes down the middle with their ramps shoehorned in. (In a sense, it was similar to how it would be if the Jersey Turnpike's "dual-dual" format were extended all the way to the southern terminus, but the "inner drive" ramps were constructed on the left instead of on the right. Not a perfect analogy, but similar conceptually.)

With that said, not surprisingly the OP still hasn't responded to my point about the "passing lane" problem.

[interstatefan990]

What about left exits that lead to a freeway-to-freeway ramp? You could theoretically exit left and then have a flyover/other ramp to a normal right-side merge. I imagine it would be much more costly to construct a right-side exit ramp for certain layouts of freeways, like where the other road is far left of the original one. I'm sure there are real-life examples of this.

[1995hoo]

BTW, I can think of a place where left- and right-side onramps enter at essentially the same location: https://goo.gl/maps/55VDBhN3LkKZ2wAC7

[NE2]

Sexy.

[kernals12]

Well, understand that highways are built with ramp locations in mind.  You are all looking at *existing* highways that don't have space in the median for ramps.  Build a new highway from scratch, and you could much more easily design it with ramps in the median, vs on the right.

Or modify a highway, for that matter. The I-495 HO/T lanes in Virginia use almost entirely left-side ramps, with a few exceptions in the Tysons Corner area. That was a case of an existing road that generally had no median being rebuilt into a wider road that still has no median but has the express lanes down the middle with their ramps shoehorned in. (In a sense, it was similar to how it would be if the Jersey Turnpike's "dual-dual" format were extended all the way to the southern terminus, but the "inner drive" ramps were constructed on the left instead of on the right. Not a perfect analogy, but similar conceptually.)

With that said, not surprisingly the OP still hasn't responded to my point about the "passing lane" problem.

Actually I did respond

[kphoger]

I mean that if left hand ramps were the norm, then for safety reasons, the passing lane would be the right lane for the same reason that the left lane is the passing lane in our world where right hand ramps are the norm

I'm not entire sure it would.  On two-lane roads, one would still pass on the left.  It would be a strange situation in which pass on the left is the norm on some highways but pass on the right is the norm on others.  Strange enough that it might not even develop.

[1995hoo]

Well, understand that highways are built with ramp locations in mind.  You are all looking at *existing* highways that don't have space in the median for ramps.  Build a new highway from scratch, and you could much more easily design it with ramps in the median, vs on the right.

Or modify a highway, for that matter. The I-495 HO/T lanes in Virginia use almost entirely left-side ramps, with a few exceptions in the Tysons Corner area. That was a case of an existing road that generally had no median being rebuilt into a wider road that still has no median but has the express lanes down the middle with their ramps shoehorned in. (In a sense, it was similar to how it would be if the Jersey Turnpike's "dual-dual" format were extended all the way to the southern terminus, but the "inner drive" ramps were constructed on the left instead of on the right. Not a perfect analogy, but similar conceptually.)

With that said, not surprisingly the OP still hasn't responded to my point about the "passing lane" problem.

Actually I did respond

Actually, you didn't.

[hbelkins]

I don't really have an issue with left exits, given they're adequately signed. Heck, right exits can be problematic if they aren't signed well in advance. Years ago, I was traveling in Tennessee on I-81 and was unable to exit because the first exit sign was a 1-mile advance, I was in the left lane passing trucks, and there was not a suitable gap in traffic for me to get over to the right lane until I was right at the exit. So I had to go to the next exit and backtrack on surface routes, which was more of a minor annoyance than a terrible inconvenience.

But left entrances ... aargh. The two I probably hate most are I-66 west onto I-81 south, and the infamous Poughkeepsie "bowtie."

[Rothman]

Poughkeepsie bowtie would have worked well...if traffic volumes hadn't climbed.  I like that interchange.

[kernals12]

From an article about the Illinois DOT's plans to remove Oak Park's infamous left exits

"Even highway exits go to the left in Oak Park,"  goes the old joke. In 1961, Oak Park's then-village president J. Russell Christianson lobbied hard to get left-hand exits when the "Congress Expressway"  was built, seeking to decrease loss of property and noise levels. The name of the expressway changed to the "Eisenhower,"  but the ramps stayed on the left.

And here's an example of the difference in ROW requirements
Normal: https://countyroads.sccgov.org/sites/g/files/exjcpb681/files/Central%20Expy_Lafayette_Alt%201.pdf
Left Exit and Entrance: https://countyroads.sccgov.org/sites/g/files/exjcpb681/files/Central%20Expy_Lafayette_Alt%202.pdf

This layout creates what is basically a SPUI interchange, with all the associated traffic benefits and at a lower cost at that.

[Occidental Tourist]

It seems to me that the problems caused by left hand ramps is solely due to them not being normal. If they were the norm then the rightmost lane would be the fast lane and the problem goes away. I wonder why they chose right hand ramps in the first place.

This.  Imagine how easier it would be to plan and design highways if the left lanes were the slow/merge lanes and all highways exited to the inside lanes rather than the outside lanes.  No dual signalization at on-and-off ramps.  Every freeway entrance would effectively be a SPUI.  And expanding left turn capacity for entering a freeway wouldn't impact signal timing or the effectiveness of the corresponding offramp.  And imagine how much less right of way would be needed to expand freeways at crossroads.

[kphoger]

Wouldn't the interchanges cost more to construct, though?  At a traditional diamond, only the crossroad needs to have a bridge.  If the ramps connect to it midway, then they need to be overhead as well.

[kphoger]

And imagine how much less right of way would be needed to expand freeways at crossroads.

Now imagine the headache of expanding the ramps, though.

[GaryV]

If the road changes from freeway to expressway, the slow lane would need to switch from the left to the right.

[kernals12]

And imagine how much less right of way would be needed to expand freeways at crossroads.

Now imagine the headache of expanding the ramps, though.

But since it would be a SPUI, the ramps would have more capacity and would be less likely to need expansion.

Wouldn't the interchanges cost more to construct, though?  At a traditional diamond, only the crossroad needs to have a bridge.  If the ramps connect to it midway, then they need to be overhead as well.

You could use embankment.

[Brandon]

From an article about the Illinois DOT's plans to remove Oak Park's infamous left exits

"Even highway exits go to the left in Oak Park,"  goes the old joke. In 1961, Oak Park's then-village president J. Russell Christianson lobbied hard to get left-hand exits when the "Congress Expressway"  was built, seeking to decrease loss of property and noise levels. The name of the expressway changed to the "Eisenhower,"  but the ramps stayed on the left.

And here's an example of the difference in ROW requirements
Normal: https://countyroads.sccgov.org/sites/g/files/exjcpb681/files/Central%20Expy_Lafayette_Alt%201.pdf
Left Exit and Entrance: https://countyroads.sccgov.org/sites/g/files/exjcpb681/files/Central%20Expy_Lafayette_Alt%202.pdf

This layout creates what is basically a SPUI interchange, with all the associated traffic benefits and at a lower cost at that.

And those left exits are terrible pieces of shit (having to pass them virtually every workday).  They clog up the Ike in the area due to vehicles cutting left to exit at both Austin and Harlem.  And then they clog from slow-moving traffic entering on the left. The Oak Park section should've been built with proper service drives and right-hand exits.

[kernals12]

From an article about the Illinois DOT's plans to remove Oak Park's infamous left exits

"Even highway exits go to the left in Oak Park,"  goes the old joke. In 1961, Oak Park's then-village president J. Russell Christianson lobbied hard to get left-hand exits when the "Congress Expressway"  was built, seeking to decrease loss of property and noise levels. The name of the expressway changed to the "Eisenhower,"  but the ramps stayed on the left.

And here's an example of the difference in ROW requirements
Normal: https://countyroads.sccgov.org/sites/g/files/exjcpb681/files/Central%20Expy_Lafayette_Alt%201.pdf
Left Exit and Entrance: https://countyroads.sccgov.org/sites/g/files/exjcpb681/files/Central%20Expy_Lafayette_Alt%202.pdf

This layout creates what is basically a SPUI interchange, with all the associated traffic benefits and at a lower cost at that.

And those left exits are terrible pieces of shit (having to pass them virtually every workday).  They clog up the Ike in the area due to vehicles cutting left to exit at both Austin and Harlem.  And then they clog from slow-moving traffic entering on the left. The Oak Park section should've been built with proper service drives and right-hand exits.

You're further proving my point that the only real problem with left hand ramps is that they're unfamiliar to drivers. I imagine that tomorrow's driverless cars will be programmed to smoothly move across the freeway in anticipation of left hand exit ramps and cooperate so that left hand entrance ramps don't cause traffic snarls.

[kernals12]

If the road changes from freeway to expressway, the slow lane would need to switch from the left to the right.

I guess it would be instinctive, drivers would quickly figure out that the slow lane is the one with all the exits and entrances.

[hotdogPi]

If the road changes from freeway to expressway, the slow lane would need to switch from the left to the right.

I guess it would be instinctive, drivers would quickly figure out that the slow lane is the one with all the exits and entrances.

MA 2 in Fitchburg? The cemetery on MA 128 in Peabody?

[Rothman]

A hodgepodge of thoughts:

The Thruway EB between I-890 and Free I-90/I-87 (Exit 24):  Exit 24 is a left off-ramp and commuters from Schenectady do plant themselves in the left lane no matter how slow they're travelling.  It's a classic example of why left off-ramps are bad, no matter how much room you give them.

I-690 to I-481 NB is a left on-ramp.  I don't think it is that problematic as is -- traffic volumes are low enough to allow for poor mergers that don't speed up enough.  But, I believe this will also be addressed in Phase 1 of the I-81 project.

There's also that left on-ramp from Maryland House (I believe) onto I-95 SB that can be a disaster if you get behind someone not willing match the speed of traffic.  It's built long enough, but if you get stuck behind someone scared to go over 55, it's still harrowing.