It's not your imagination. There are months when there are more accidents on Interstate 680 in the San Ramon Valley.
What causes these spikes isn't really clear.
It's not always the weather or the annual time changes. Road work can be a factor, although it's not always the cause either.
CHP figures show there were 50 accidents in which the agency took reports on along Interstate 680 between Alcosta Boulevard in Dublin and Diablo Road in Danville between Sept. 1, 2010 and Nov. 30, 2010.
This was before Caltrans crews began the major rehabilitation work on the freeway.
In the same time period this year, there have been 70 accidents worthy of a CHP report along that portion of Interstate 680.
Caltrans road crews have been busy during these months.
Broken down, the section between Dublin and Crow Canyon Road in San Ramon appears to be a bit more accident prone than the more northern half between Crow Canyon and Diablo Road.
There were 32 accidents in the southern half between Sept. 1 and Nov. 30, 2010 while the northern sector recorded 18 collisions.
The southern sector was the site of 41 accidents during those three months this year while the northern section experienced 29.
Here's a month-by-month comparision of the accidents reported on both sections.
September 2010 -- 13
October 2010 -- 12
November 2010 -- 25
September 2011 -- 33
October 2011 -- 15
November 2011 -- 22
The spike in November 2010 is a mystery. There was no major road work and the National Weather Service monthly weather report for the region doesn't note any significant events.
The surge in September 2011 may not be as confounding. The weather was relatively uneventful. The NWS report shows it rained lightly on only two days and there were only six days of fog.
The weather in October was actually more winter-like. There were two days of heavy rain, six days of light rain and 10 days of fog. October is also when clocks are turned back an hour, creating a darker, and possibly more dangerous, evening commute.
Yet, there were seven fewer collisions that month than the previous month.
However, Caltrans crews were busy in September. Their monthly review shows the crews, besides their normal rehab work, began putting down new asphalt about Sept. 20. That required the temporary re-marking of lanes on the freeway.
One theory is the initial changes could have created problems for drivers, causing some of the accidents. By October, motorists had adjusted to the alterations.
CHP officer Steve Creel said road construction is one of the factors the agency considers when there is an upsurge in accidents on a freeway.
"It's not unusual to see an increase in collisions," he said.
Creel also said rainy weather, when it happens, can be just as big of a factor. He noted there appears to be a microclimate in the Crow Canyon and Bollinger Canyon Road areas. The weather seems to sweep down off the Las Trampas hills and create more rain and wind there.
That may explain the additional accidents in the southern half of that section of I-680.
Creel points out that 160,000 cars use Interstate 680 in the San Ramon Valley on an average day. He said there is, on average, less than a crash a day on that section of the freeway. Interstate 580 in the Tri-Valley actually has more collisions.
"I don't know that I would call 680 crash prone," he said.