On-ramp decreasing-radius turns?

Is it just me, or do the preponderance of cloverleaf freeway on-ramps have decreasing radius turns? If so, why did anyone think it was a good idea to slow a car down as much as possible just before it has to merge with high-speed traffic?

Me thinks you are looking for a problem where there is none. Most limited access highways have a merging lane after the ramp .

Probably constricted by the amount of land available without purchasing more land.


Space and construction costs. Rural areas have longer ramps than in the big cities. Changes in the degrees on off ramps is what I dislike. Mild then sharp.

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That’s one reason you won’t see cloverleaf designs now. They were obsolete in 1970.

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There is a nasty one in I-35 and 412 here in OK. The one exit while going north on I-35 and taking the 412 exit west is 25 MPH as it merges with the end of the turnpike. With rain, snow, or ice even 25 MPH can be iffy when merging with 70 MPH traffic. The lane is also very narrow with a high curb and there are hundreds of undeveloped acres around it. The radius on that turn is very small and any inattention while watching for turnpike traffic can easily lead to curb strikes.

They had that entire interchange under re-construction a few years ago and we thought they might resolve that problem. No such luck. They rebuilt it back just the way it was; sharp turn, narrow lane, and very little merge room. Only difference was new concrete.
Two years of construction work all to end up with the same result.

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There was a highway on ramp on my daily drive that required a left turn to enter the ramp. Ten years ago, a clover loop was built moving the ramp to the right side of the street, a right turn to enter the highway, no more stopping for the left turn traffic light. I can reach 70 mph before the end of the on ramp with my under powered car unless the car in front of mine is planning to merge in at 35 mph.

What I really like (NOT) is in the Stamford/Cos Cob CT. area is there are no merge areas on the on ramps even to route 95. It’s always quite exciting coming around a 15 or maybe 20 mph curve, blindly right into 60+ mph traffic. Or just stopped cars on the ramp.

Obsolete design, a good example of these tight cloverleafs is the Baltimore-Washington Parkway, state of the art in 1954, two years before the 1956 Eisenhower Interstate Highway Act.
One of the first Federal highways and at the time the planned route was largely rural so plenty of land was available but a lack of experience designing high speed highways.

As a limited access highway it was a vast improvement over Washington Blvd/Route 1 and wonder of it’s time but besides tight cloverleafs additional features from the “good old days” included short merge lanes, no emergency shoulders, concrete curbing and very limited lighting.

It’s still in use today and the speed limit is still 55 but with the growth of the suburbs it’s completely hemmed in with no chance of expansion.

And I’m glad it can’t get expanded.
It’s a parkway, not an expressway.
It should be a leisurely alternative to I-95, which runs parallel.

The cloverleaf at the junction of I-93 and I-95 (aka 128) is one of the oldest in the country. Over 400,000 thousand cars a day pass through this outdated design. MA state DMV has been talking about upgrading it for decades. The problem I see is that there are a lot of businesses th at may need to be moved/torn down to accommodate any change. It’s a mess. I try to avoid that area at all costs during morning and rush hour traffic.

Cloverleaf project moving slowly, but not dead yet | Middlesex East | homenewshere.com

It is a commuting thoroughfare away practical matter. A lane was added north of MD175 for Arundel Mills traffic, but it is not the BW Parkway that far north, only south of MD175. It becomes DC295 south of the DC beltway, but I’m not sure exactly where.

I use the MD32 interchange off the BW Parkway during my commute. The cloverleaf entrance onto MD32 west from 295 north is dangerous enough that I slow approaching the merge rather than speed up. Fitting in front of or behind oncoming traffic that wants to exit onto 295 south is difficult since the merge is so short. Ideally I could enter the merge at 55 mph but that is way too dangerous.

I completely agree with both of you but:

  1. It’s the only “somewhat limited access route” going northbound from downtown to the Capitol Beltway.
  2. From the Beltway north I 95 is already 4 lanes, always crowded and frequently backed up.
  3. Same with 70S which heads more westerly.
  4. Leaving the obsolete BW Parkway as the only limited access, no traffic lights alternative

More to the point, Washington DC is rapidly becoming an example of our urban post-automobile future. Overcrowded roads, no room to expand and outrageous city parking costs has made downtown homes and homes near Metro stops particularly attractive and expensive.

Maybe telecommuting will make a difference but I don’t see the current generation as willing to hop into their car and make that 3-4 hour mind numbing daily commute.

… especially since the percentage of younger folks who are interested in owning/driving a car is much lower than for the previous couple of generations.

Do you mean it seems like the turn gets sharper the further along in the circle you go? Or do you mean that over the years, on newer road construction, the turn radii seem to be designed smaller than older construction?

There’s one freeway/freeway interchange in the San Jose area that’s a full cloverleaf. If it was my turn to drive the group of coworkers to lunch, they would prod me – instead of just proceeding straight through that intersection – to divert & drive around all four circles first, before continuing on to lunch, sort of like an amusement ride.

I meant the first one, where the turn gets sharper the further along the circle you go. The one I use the most has undergone one re-design and is the freeway is undergoing considerable construction. Originally, like most where I live (Sacramento, CA.), it had a very short merge lane (less than 100 feet) but is now about 500 feet after the re-design. The freeway construction will most likely not change this. Short merge lanes are endemic here; entering the freeway in an older car can be quite challenging unless it’s a muscle car.

Not any more. All new or revamped on ramps have very little merge room.

Also not anymore. All the new construction ramps terminate abruptly, even out in the country. There are two rural on-ramps to I 40 near me that used to have a long merge lane. They came along and put a barrier between the on ramp and the right lane until near the end of the on ramp.

My guess is that they are doing this because of the morons that would use the merge lane as a passing lane.

That might apply where you are but the contruction redo on I-44 near Tulsa ,OK hasplenty of space on the on ramps . Of course it will not be completed for another 2 years but it seems to be well thought out.

You mean they haven’t put the barriers in yet. All the on ramps around here, well almost all would have enough room if it weren’t for the barriers.

Does the barrier make the on ramp shorter? There is typically a solid white line in the start of the on ramp that 1 out of 4 drivers cross to merge before the drivers ahead. A barrier would keep drivers from merging at too slow of speed.