Charleston On-Ramp Needs to Go

The entrance from Charleston Rd to southbound 101 in Mountain View, CA should not exist. It is dangerous. It slows down traffic. It is unnecessary. no on-ramp

Dangerous

Cars entering the freeway can't get up to speed.

The on-ramp is only 150 feet. This is not long enough. The average length of the 10 nearest on-ramps is 978 feet. More than six times as long. on ramp length

The merge lane is 300 feet. It takes 5 seconds to drive 300 feet. Can't merge in that time? Loop back around and try again!

It is unreasonable to expect drivers to go from 35mph to 65mph, and then merge, on 450 total feet of roadway. merge lane ramp length

Drivers who know about the short on-ramp start speeding up early. In my observation the majority of drivers are going over 45mph through the intersection during midday. This makes it dangerous for traffic turning left onto Charleston Rd. turning in front of accelerating traffic

Slow

Vehicles entering from Charleston Rd cannot reach highway speed before merging. This slows down highway traffic.

Using acceleration data for medium and heavy trucks, we can calculate a medium or heavy truck will be going 40-45mph after merging. This slows down freeway traffic. cars entering 101 south from Charleston Rd

A Truck uses the Charleston Rd freeway entrance during midday. Note the vegetation blocking the view of the highway traffic.

Unnecessary

It is only 0.2 miles (1 minute) to the Rengstorff interchange on-ramp. This entrance is longer, and the merge lane is over a mile long. The Charleston ramp is superfluous. distance to nearest on-ramp

Appendix: Theories on Why the On-Ramp was Built

The CA Dept of Transportation Highway Design Manual states:

An interchange is expected to have an on- and off-ramp for each direction of travel. If an off-ramp does not have a corresponding on-ramp, that off-ramp would be considered an isolated off-ramp. Isolated off-ramps or partial interchanges shall not be used because of the potential for wrong-way movements.

Emphases in the original

The San Antonio interchange half a mile away has a southbound exit, but no southbound entrance. So despite being much closer to Rengstorff than San Antonio, I believe this entrance was created to meet the guidelines. SB 101 San Antonio Entrance and Exit

That is, it exists because of bureaucracy, not because anyone thought it was a good idea.

But we can see this rule is not inflexiable. Less than three miles away — at the interchange of 85 and Moffett — the northbound exit is isolated. There is no northbound on-ramp. Isolated NB 85 exit to Moffett Blvd