I happen to live in Hayward and I am very familiar with this
particular bottleneck. Although I have not read the article by Cassidy
et. al., I think it is worth pointing out that there are unique
features that affect this particular stretch of interstate - to my
mind, it is not a particularly representative sample. What makes this
section of highway unique is that:

1.) The shoulder lane north of Tennyson on I-880 is also a heavily
used exit lane from I-880 for the off-ramp immediately north of the
study location (the Highway 92/Jackson Street cloverleaf);

2.) The distance from where the Tennyson traffic enters and Highway
92/Jackson Street exists is very short (less than ¾ mile),
complicating both entry to and exit from I-880;

3.) Many cars entering from Tennyson immediately exit onto Highway
92/Jackson Street and never merge into the through lanes on I-880;

4.) There has been major reconstruction at the Highway 92/Jackson
Street cloverleaf and lane alignment modifications in the study area
in recent months, which continues to complicate navigating the study
area (I have no idea when the study took place, so this may or may not
be a factor); and, most importantly

5.) The bottleneck on I-880 along this stretch of highway, and
particularly during rush hours, is caused by a heavy stream of drivers
attempting to exit at Highway 92/Jackson Street, which is a major
shortcut across Hayward to I-580 (check it out on Google Maps/Earth).
In other words, this backup at rush hour is caused by drivers on I-880
exiting at the next off-ramp immediately north of the study area (at
Highway 92/Jackson Street), rather than drivers merging onto I-880
from Tennyson. The real reason drivers stay in their lanes during rush
hour is because many of them do not want to lose position for their
exit at the following Highway 92/Jackson Street cloverleaf, which can
be tricky under any circumstances, but is particularly bad at rush
hour when traffic restrictions in the diamond lanes are in effect
(rush hour begins early in Hayward because of the widespread use of
flex-time in Silicon Valley). How do I know this? Because I drive this
section of I-880 on a regular basis and I am one of those frozen
drivers who are just praying they make it into the shoulder lane and
off the freeway at Jackson.

I am a regular user of Diamond Lanes and I would like to believe that
they help to reduce traffic. Because of the unique features of this
particular stretch of I-880, I would be reluctant to draw such a
conclusion from this study.

Thank you for your informative and well written blog.

Yours truly,
Robert E. Clucas