Drainage Bars are placed in the gutter area for water to flow into them during rainstorms and flow eventually into rivers, etc. Until circa 1970, these were aligned with the road, enabling a bicycle wheel to fall through. If the front wheel falls through, it means a sudden flip-over of the bicyclist and a good chance of head injury. (This happened to a friend of mine.) If the rear wheel falls through, it destroys the rear wheel. (This happened to me). Most have since been changed to bars perpendicular to the road or in both directions, except on freeways where bicycles are banned.
California Streets and Highways Code section 161 provides:
"On construction projects, the department shall install on the surface of state highways upon which the operation of bicycles is permitted only those types of grates which are not hazardous to bicycle riders."
As you can see, this applies only to the Department of Transportation (Caltrans) and not to local agencies, so strictly speaking the grates may not be illegal (but see below). They are, however, in violation of good engineering practice, and a source of liability for the responsible agency under the Government Code, which provides that agencies are liable for a dangerous condition of public property that creates a substantial risk of injury when used with due care in a reasonably foreseeable manner. Parallel bar drain grates that allow a bicycle wheel to fall into a slot certainly create a risk of injury, including permanent disability and death.
Caltrans follows a design standard called the Highway Design Manual (HDM). Although most of the HDM's provisions are not legally binding on local agencies, those agencies normally follow it as evidence of good engineering practice that serves as a defense against liability. Most agencies have explicitly adopted the HDM as their design standard.
Certain HDM provisions, primarily involving bikeways, do happen to be binding under Streets and Highways Code section 891:
"All city, county, regional, and other local agencies responsible for the development or operation of bikeways or roadways where bicycle travel is permitted shall utilize all minimum safety design criteria and uniform specifications and symbols for signs, markers, and traffic control devices established pursuant to Sections 890.6 and 890.8."
One of these mandatory criteria is at HDM Index 1003.6(3) (http://www.dot.ca.gov/hq/oppd/hdm/pdf/chp1000.pdf):
"Drainage inlet grates on bikeways shall have openings narrow enough and short enough to assure bicycle tires will not drop into the grates (e.g., reticuline type), regardless of the direction of bicycle travel. Where it is not immediately feasible to replace existing grates with standard grates designed for bicycles, 25 mm x 6 mm steel cross straps should be welded to the grates at a spacing of 150 mm to 200 mm on centers to reduce the size of the openings adequately.
"Corrective actions described above are recommended on all highways where bicycle travel is permitted, whether or not bikeways are designated."
The first sentence, using the word "shall," is mandatory on bikeways, so your grates are illegal if those streets have bike lanes. Even if they don't, the provision taken as a whole constitutes very strong evidence that sound engineering practice everywhere except prohibited freeways and toll bridges requires bicycle-safe drainage grates.
Note also HDM Index 837.2(2), in the chapter on Roadway Drainage (http://www.dot.ca.gov/hq/oppd/hdm/pdf/chp0830.pdf):
"If grate inlets must be located in roadway areas where cyclists may be expected to travel, bicycle proof grates are to be specified. Bicycle proof grates are shown on Standard Plan D77-B."
Standard Plan D77-B, "Bicycle Proof Grate Details," can be found at
There is a variety of acceptable designs. All this constitutes overwhelming evidence that good engineering practice calls for bicycle-safe grates, and that they are easily provided or retrofitted.
Also see: list of bicycle articles.