Where have all the off-ramps gone?
June 12, 2015 11:41 AM   Subscribe

I commute on Central Expressway (County Route G6) between Santa Clara and Palo Alto CA daily and have a question as to it's history....

The intersections of Central and both the San Thomas and Lawrence Expressways have what appears to be the infrastructure for on-ramps and off-ramps that had been initially built and then abandoned in favor of some really cumbersome through-the-businesspark transitions. Anyone know the history here? Why weren't these original ramps used?
posted by Mr.Me to Travel & Transportation around California (3 answers total) 3 users marked this as a favorite
I'm not familiar with these specific interchanges, but looking at the aerial photos, I would imagine that the original ramps were used at first. But, those ramps were very short, so its likely that traffic was backing up. By doing what they did through the business park, more cars can be stored along the ramp without impacting either of the two crossing roads.

But that's one strange interchange at Lawrence, with the parking lots having direct access to the highway...
posted by hwyengr at 11:56 AM on June 12, 2015 [1 favorite]

I’m not familiar with this area either, but looking at google earth my best guess would be that removing those ramps had to do with conflicting traffic movements and speed, plus what hwyengr said about the ramps being short. If you think about 2 cars in what I assume was the original layout, one going south on Lawrence that wants to go east on Central and one going east on Central that wants to go south on Lawrence. The south to east car would take the loop that is Enochs St. However, as it is speeding up to enter Central, that will conflict with the car slowing down to take the short little ramp to turn and go south on Lawrence. It looks like there used to be maybe 300 feet of “weave distance” there and that very short, especially on a roadway with a lot of traffic. Add in the probable back-ups from the short ramps and you have quite a mess with stopped exiting cars and entering cars trying to speed up. Switching to the set-up that is there now removed that conflict.

I assume that this whole weird set-up is due to the roadways here being switched to a grade separation and not a stop light long after everything in the area had built up and no room was available for more traditional interchange types. If you look to the west at the interchange with Wolfe Rd you can see how putting that style interchange in would at least take out the 4 buildings right at the intersection and probably parts of parking lots to the east and west. Putting larger, higher speed roadways into built up urban areas can require lots of interesting solutions.
posted by Sabby at 12:42 PM on June 12, 2015 [2 favorites]

I've noticed these and they remind me of the 5mph Highland Park exit ramps off the Pasadena Freeway, one of the oldest, built before traffic moved so fast. Same thing going on with the Central Expressway, but there they had room to squeeze in longer ramps.
posted by Rash at 12:48 PM on June 13, 2015

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