Diamond function for a parclo interchange

[jakeroot]

So I'm taking a drive in Olympia, WA the other day, and I can't help but notice this:



I've circled the oddity in case you can't figure it out. Why would someone drive straight across here (exit ramp to entrance ramp), other than that they made an error in exiting the freeway? It would be cheaper to just build it as a slip ramp like most parclos. In the mid 20th century when we had billions of dollars to spend on road construction, I can see this. But today, we can barely gather enough money for a signal. It just doesn't seem necessary. I know you'll hammer me for not considering all road users. I am fully prepared to accept the hammering.

I know this is desirable in situations where the freeway goes under the service road, and oversize loads can't meet the clearance, but in this situation, the freeway goes over the service road so that function does not apply.

[agentsteel53]

wouldn't the signal be mainly for drivers exiting the freeway and wanting to turn left?  (westbound to southeast-bound, assuming north is toward the top of that image)

or does another ramp that I'm not seeing take care of that movement?

[jakeroot]

wouldn't the signal be mainly for drivers exiting the freeway and wanting to turn left?  (westbound to southeast-bound, assuming north is toward the top of that image)

or does another ramp that I'm not seeing take care of that movement?

Pretty massive screw up on my part. I'm talking about the movement from exit ramp to entrance ramp. You can see the arrow on the road points left and straight, indicating you may continue onto the entrance ramp from the exit ramp, or turn left. The signal is to allow left turns from the exit ramp onto Pacific.

[NE2]

Seems like a fairly minimal increase in cost over not including that movement. I don't see any bus stops on the ramps, so it's probably for cockups.

http://maps.google.com/maps?hl=en&ll=28.363084,-81.565289&spn=0.005414,0.007086&gl=us&t=k&z=18 is a stranger example, where a completely redundant signal was installed. I have seen Disney buses make the left, perhaps if they're then making another left soon.

[jakeroot]

Seems like a fairly minimal increase in cost over not including that movement. I don't see any bus stops on the ramps, so it's probably for cockups.

http://maps.google.com/maps?hl=en&ll=28.363084,-81.565289&spn=0.005414,0.007086&gl=us&t=k&z=18 is a stranger example, where a completely redundant signal was installed. I have seen Disney buses make the left, perhaps if they're then making another left soon.

Cockups indeed. On the ramp you posted, it's odd how many tire marks there are, on the redundant ramp.