The signal timing, and the k-rail, and the striping all contributed. Over the next 3 days, they are working on most of that. They were going to finish it the following week, but now it's been moved back. We'll see if that improves things substantially.
Here's the recent update from Caltrans:
San Pedro Creek Bridge Construction Update (State Route 1) Pacifica
San Mateo County- The California Department of Transportation (Caltrans) will
begin final paving operations on U.S. State Route 1 (northbound/southbound)
between Post Mile 40.6 (Ace Hardware) to Linda Mar Boulevard in Pacifica,
starting Tuesday, September 8, and completed by Thursday, September 10, from
7:00 PM to 6:00 AM.
San Pedro Avenue will have one-way traffic control with flaggers: September 8,
7:00 PM to 6:00 AM
Linda Mar Boulevard & State Route 1 will have various lane closures: September
9, 7:00 PM to 6:00 AM
State Route 1 will have alternating lane closures in both directions, and
limited one-way traffic control: September 10, 7:00 PM to 6:00 AM
Note: This work will include grinding and paving operations at the intersection
of Linda Mar Boulevard and State Route 1.
The paving work will affect signal timing for the entire week. Electrical work
that controls the Route 1 and Linda Mar intersection will be worked on during
the week of September 14, original signal timing will be restored by mid-week
of September 14.
North and southbound temporary striping will be removed and replaced with
permanent striping the week of, Monday September 21 and completed by Thursday,
September 24, between the hours of 7:00 PM to 6:00 AM.
Final paving will restore lanes both north and south of the bridge back to the
original configurations. The area between the bridge and Linda Mar Boulevard
will have two lanes starting closer to the bridge.
Changeable Message Signs have been posted in advance of the construction zone.
Final construction for this project will be completed by October, 2015.