There are very specific rules contained in the CAMUTCD as to what signage and striping is required when there is an open trench in or adjacent to the roadway. The requirements are based on the trench depth and distance from the roadway.
Here is the excerpt from the CA MUTCD. Note that standards are mandatory and are usually indicated by the word “shall” (refer to the manual for original formatting).
Section 6F.103(CA) OPEN TRENCH Sign (C27(CA))
Standard:
01 The OPEN TRENCH (C27(CA)) sign shall be used in advance of open trenches in/or adjacent to roadway.
02 The edge of the traveled way shall be defined by edge line delineation consisting of appropriate markers or striping. Edge line delineation shall be white when located on the right of traffic and yellow when located on the left of traffic.
Guidance:
03 Trenches in excess of 0.15 feet in depth but not exceeding 0.25 feet in depth that are less than 8 feet from the edge of traveled way should be identified by LOW SHOULDER (W8-9) signs set in the trench adjacent to the edge of pavement at intervals not to exceed every 2,000 feet.
Option:
04 Portable delineators may be placed at intervals not to exceed 100 feet in lieu of edge line delineation.
Standard:
05 Trenches in excess of 0.25 feet but less than 2.5 feet in depth that are less than 8 feet from the edge of traveled way shall be identified by alternating C27(CA) and NO SHOULDER (C31A(CA)) signs set in the trench at intervals not to exceed 2,000 feet.
Guidance:
06 Channelizers (CA) or portable delineators should be placed 2 feet to 6 feet outside of the edge line at 100 feet intervals for the conditions described above.
07 Trenches in excess of 0.25 feet in depth but not exceeding 2.5 feet in depth that are 8 feet to 15 feet from the edge of traveled way should be identified by C27(CA) signs set in the trench at intervals not to exceed every 2,000 feet. Portable delineators should be placed at 200 feet intervals within 2 feet from the edge of the trench and at 100 feet intervals for edge conditions exceeding 0.5 feet in depth.
08 Trenches in excess of 0.5 feet in depth but not exceeding 2.5 feet in depth that are more than 15 feet from the edge of traveled way at locations where a recovery area was available prior to construction should be identified by placing delineators at 200 feet intervals within 2 feet from the edge of the trench and by placing C27(CA) signs in the trench at intervals not to exceed 2,000 feet.
Standard:
09 Signing for trenches in excess of 2.5 feet in depth shall be based upon engineering judgment or studies (as noted in Section 1A.09) to ensure proper visibility of barricades and signing.
Support:
10 Refer to Tables 6F-101(CA) and 6H-3.