Neat off-ramp/on-ramp combo

[moribundman]

Zipping along the higway, coming out of a curve, you suddenly see vehicles going 30 merge from a very short on-ramp merge into dense 70 mph traffic. At the same time, cars cut across all lanes to make it to the off-ramp that comes right AFTER the on-ramp. I think it's easy to see how cars, criss-crossing each other, especially while accelerating or decelerating, isn't exactly a good idea. The whole on/off-ramp combo is maybe 50 yards long. Sometimes, a black and white sits there, hoping to slow down people. Problem is, due to the curve and a view-obstructing overpass you can't even see the on/off-ramp, or the cop, until you are only 3 seconds away from it. That's one crazy spot in Marin county.

 

[brianl703]

Sounds like a problem that collector-distributor lanes would fix (if they can fit them in there..might take extensive surgury). If you don't know what CD lanes are--imagine a physically separated lane that starts perhaps 150 feet before the on ramp and continues 150 feet past the on ramp. The only traffic that the entering ramp traffic has to deal with is other traffic that is exiting--and that traffic will be going much slower than 70MPH. In addition, the entering ramp traffic gets more acceleration lane, and the exiting ramp traffic gets more deceleration lane.

 

[moribundman]

There's no space for a CD lane in the above-described spot -- not without filling in some of the Bay and demolishing part of an industrial area. Only recently they have expanded parts of 101 to four lanes. They simply don't have the money to fix up the highway to meet the requirements of increasing traffic. Not even a $5 bridge toll has slowed down traffic. And yes, we have plenty of CD lanes on other stretches of 101. However, on our CD lanes, we do go 70 and even faster.

 

[moribundman]

What bothers me most in the above case is the placement of the on-ramp BEFORE the off-ramp. That goes totally against common sense and there is no good reason to ever build it that way in the first place. I can only imagine when this thing was designed they had so little traffic they could have integrated a roundabout into the highway.

 

[brianl703]

Placing the on-ramp before the off-ramp is typical for a cloverleaf interchange, but the diagram does not show the rest of it so I have no idea if that is a cloverleaf interchange or what.

 

[jsharp]

What his diagram shows is the common configuration for 1/2 of a cloverleaf's ramps. I hate them too but sometimes there's not enough room to give any kind of accelelration de-acceleration distance.

 

[brianl703]

Usually a diamond interchange is done when there's limited space. Do those ramps go to a traffic light or what?

 

[brianl703]

PA's solution for ramps without sufficient distance is a big YIELD sign.

 

[T-Keith]

Seems like a normal cloverleaf to me. If some of you guys saw some of the roads here in MN you would lock yourself in your house and sell your car. On one particular freeway I used to drive you used to have to change lanes 4 times in about 5 miles just to stay on the same road. What seems to help these cloverleaf interchanges is when they extend the lane beyond the off ramp for a ways allowing the slow moving traffic a chance to merge. -T

 

[kenw]

this is a typical old-design ramp system with the entrance prior to the exit. We still have those here in old places, but he newer designs have the exit ramp prior to the entrance ramp. It's a small change that makes a huge difference.

 

[Matt_S]

We have several of those interchanges around this area, so I can totally empathize with the problems they cause. It's a bad design, plain and simple. There are several cloverleaf-type interchanges around here that don't cause that same problem, though. Those are a sort-of partial-cloverleaf. There's an off ramp before the cloverleaf. The cloverleaf only lets traffic from one direction of the surface street enter the freeway. Traffic from the other direction of the surface street enters further down the freeway on a more traditional ramp. Those still aren't the best, but they're an improvement.

 

[moribundman]

Having an entrance right before an exit may well be "standard,"common," and even "normal," but it's also nuts. In the shown case, the off-ramp ends at a traffic light about 250 yards from the beginning of the off-ramp. The on-ramp diverts from another road and lets the average car get up to about 45-50 mph by the time it'll encounter the exiting cars. So far I've witnessed accidents happen there three times in light traffic. Glass, other debris, and brake markings, indicate that a lot more is happening there. The safest time seems to be rush hour, when traffic crawls at about 3 mph.

 

[buster]

Wow thats insane. mori, are you familiar with Lake Tahoe? I'm making another trip out their in July. I always wondered if every now and then cars fall off those mountains? Their are no side rails and it seems very likely that now and then someone would fall the **** off.

 

[moribundman]

Yeah, I've been to the Tahoe area many times. I don't mind driving in the mountains at all. I'm sure accidents happen, but there's little evidence if someone goes nose-diving. Take Route 50, it's very scenic!

 

[eljefino]

Where rte 1, 128, and 95 merge going southbound in Massachusetts is like that. Two lanes have to cross and merge all at once. Some people speed up to fit in and others slow down. Plus, did I mention it's <i>Massachusetts</i>?

 

[moribundman]

I used to live in MA. Driving in Boston and surrounding areas was a piece of cake compared to metropolitan areas in California.

 

[buster]

"Take Route 50, it's very scenic!" I never been to a place as scenic as Lake Tahoe. Comming from NJ/Pennsylvania, I was blow away by the Sierra Nevada Mountains. I'll have to take Route 50. Quick question, we are flying into SanFran. What would be the most direct, scenic route to get to Tahoe? Last time I drove from their it took about 4 hours or so. Is Route 50 near Lake Tahoe? Thanks.

 

[moribundman]

buster, you can go from SFO north on 101 to SF, take I-80 to Sacramento, then take 50 to Tahoe. You can also go from SFO across the Bay via 92, then take 580 (you'll pass hundreds of windmills) towards Livermore, take 205 in Midway, then take I-5 to Sacramento, then take 50. In either case, it's really scenic only once you hit the Sierra foothills.

 

[deepsquat]

yeah, those type are very bad! we have one like that here in WA at HWY 18/I-5 interchange ...one day at 5 am I had a state trooper neary run me off the road as he came across 2 lanes of traffic to nearly side swipe me as he "merged" on to I-5 should have let hime hit me , but I am sure they would have found a way to blame me!

 

[wileyE]

I think those ramps were built when people knew how to drive.