conditions make that speed unsafe. However, because the Basic Speed Law establishes prima facie limits, not absolute ones, they can also defend against a citation for speeding "by competent evidence that the speed in excess of said limits did not constitute a violation of the basic speed law at the time, place and under the conditions then existing", per section 22351(b) of the California Vehicle Code. Thus, a driver who operates over the speed limit, but less than the usual maximum speed ( for two-lane undivided highways, isn't necessarily violating California's speed laws where the driver's speed was otherwise safe under the circumstances. Speed limits Rural freeways, such as parts of I-5, I-8, I-10, I-15, I-40, I-205, I-215, I-505, I-580, US 101 and SR 99, have speed limits. The highest speed limit on I-80 is because it passes almost exclusively through urban and mountainous areas. However, the speed limit on the San Francisco–Oakland Bay Bridge and in San Francisco is only . In downtown Los Angeles, the maximum speed limit is . This includes the entire length of the Pasadena Freeway between Pasadena and downtown Los Angeles, and portions of the Hollywood, Santa Ana, Santa Monica, and Harbor Freeways. The default limit on two-lane roads is . Some two-lane roads can be for some locations in California. However, Caltrans or a local agency can post a speed of up to after an engineering study. There is a speed limit for trucks with at least 3 axles and all vehicles while towing. In California, the maximum speed in school zones is , but may only be in effect when children are present within that school zone. Colorado The maximum speed limit in Colorado is on rural Interstate highways and the toll road portion of SH 470 (E-470), although Interstate 70 in the Rocky Mountains has a limit because of steep grades and curves and a limit at the east and west ends of the Eisenhower Tunnel. The maximum speed limit on other rural highways is . There are also basic prima facie speed limits in Colorado. on narrow, winding mountain roads in any business district in any residential district on open mountain highways Night speed limits On certain stretches of rural highways, notably US 160 between Durango and Pagosa Springs and US 550 between Durango and Silverton, nighttime speed limits are in effect during peak migratory periods for area wildlife. Speeding