Michaele Benedict wrote me the following email regarding the travel times listed on the 511.org website, which come from the same source as the times on Caltrans’s illuminated highways signs.

As I write this, my husband is sitting in traffic on 92 and will be late for his warm-up with Master Sinfonia Chamber Orchestra.  Hopefully, he will make it in time to play in the concert itself, but I feel bad because I discouraged him from going to Los Altos the long way around, based on travel times posted on your link. He left Montara an hour ago. He sat in pumpkin traffic an hour and forty-five minutes in the middle of the day today, trying to get home from a rehearsal.  Obviously these travel times from 511 are grossly inaccurate and are causing all kinds of trouble.  I hope my husband is still speaking to me after he gets home.

What has been your experience with the Caltrans travel time estimates: useful or dangerously misleading?

I received the following private message from a reader:

Several things I have noticed about the travel times.

First inbound to HMB from San Mateo.  I believe they measure the time from the light at 92 and 35.  This is painful as sometimes it can take 30 minutes to get to the light. (only about 3/4 of a mile).

2nd outbound from ELG.  The sign by surfers beach that states 6 minutes to Burger King is usually accurate.  The next measurement that says 20 minutes to 92/35 is regulary wrong.  During the tree trimming last month it said 20 minutes.  I sat at the 92/main light for 15 minutes before I turned around and went through Pacifica.

In short, you can’t count on the low times but if the sign says 45 minutes, head north.

Does anybody know how this travel time calculation is actually done?  Are there little sensors along the way that track a particular vehicles progress?  As an engineering type, I have not figured it out.

Sensors for FastTrack.

But realize that the signs aren’t telling you how long it’ll take you to travel, they’re telling you how long it took the most recent FastTrack-equipped vehicle.  Conditions could have changed significantly during that last vehicle’s trip.

I find the 511.org times generally useful, and not just for 92.

For the over-the-hill times, I mostly use LCP’s excellent graph <http://lcp.sanmateo.org/trip/current.html>, which has the advantage of showing trends.

As LW notes, the times are history, and not entirely reliable as predictions of the future. But barring accidents and Caltrans events, and considered in the context of normal traffic patters, they’re pretty good.