(Reuters) - Alphabet Inc’s (GOOGL.O) Google said on Monday it bears “some responsibility” after one of its self-driving cars struck a municipal bus in a minor crash earlier this month. 
 
 A prototype of Google's own self-driving vehicle is seen during a media preview of Google's current autonomous vehicles in Mountain View, California September 29, 2015. REUTERS/Elijah Nouvelage 
 
 The crash may be the first case of one of its autonomous cars hitting another vehicle and the fault of the self-driving car. The Mountain View, California-based Internet search leader said it made changes to its software after the crash to avoid future incidents. 
 
 In a Feb. 23 report filed with California regulators, Google said the crash took place in Mountain View on Feb. 14 when a self-driving Lexus RX450h sought to get around some sandbags in a wide lane. 
 
 Google said in the filing the autonomous vehicle was traveling at less than 2 miles per hour, while the bus was moving at about 15 miles per hour. 
 
 The vehicle and the test driver “believed the bus would slow or allow the Google (autonomous vehicle) to continue,” it said. 
 
 But three seconds later, as the Google car in autonomous mode re-entered the center of the lane, it struck the side of the bus, causing damage to the left front fender, front wheel and a driver side sensor. No one was injured in the car or on the bus. 
 
 Google said in a statement on Monday that “we clearly bear some responsibility, because if our car hadn’t moved, there wouldn’t have been a collision. That said, our test driver believed the bus was going to slow or stop to allow us to merge into the traffic, and that there would be sufficient space to do that.” 
 
 The Santa Clara Valley Transportation Authority will investigate the circumstances of the accident, Stacey Hendler Ross, spokeswoman for the Santa Clara Valley Transportation Authority, said on Monday. 
 
 She said the Google car caused minor damage to the bus, striking the “pivoting joint,” or flexible area in the middle of the articulated bus. After the crash, 15 passengers on the bus were transferred to another bus. 
 
 An investigation to determine liability is pending, she said. 
 
 John M. Simpson, privacy project director for advocacy group Consumer Watchdog, said the crash “is more proof that robot car technology is not ready for auto pilot.” 
 
 A spokesman for the California Department of Motor Vehicles said on Monday it will speak to Google to gather additional information, but added “the DMV is not responsible for determining fault.” 
 
 SOFTWARE REFINED 
 
 Google said it has reviewed this incident “and thousands of variations on it in our simulator in detail and made refinements to our software. From now on, our cars will more deeply understand that buses (and other large vehicles) are less likely to yield to us than other types of vehicles, and we hope to handle situations like this more gracefully in the future.” 
 
 There has been no official determination of fault in the crash. Google has previously said that its autonomous vehicles have never been at fault in any crashes. 
 
 The Mountain View Police Department said no police report was filed in the incident. 
 
 A spokesman for the U.S. National Highway Traffic Safety Administration declined to comment. 
 
 The crash comes as Google has been making the case that it should be able to test vehicles without steering wheels and other controls. 
 
 In December, Google criticized California for proposing regulations that would require autonomous cars to have a steering wheel, throttle and brake pedals when operating on public roads. A licensed driver would need to be ready to take over if something went wrong. 
 
 Google said in November that in six years of its self-driving project, it has been involved in 17 minor accidents during more than two million miles of autonomous and manual driving combined. 
 
 “Not once was the self-driving car the cause of the accident,” Google said at the time. ||||| Google has prided itself on the fact that its self-driving car fleet has never been responsible for any of its crashes — they've always been caused by another (decidedly more human) force — but that may have just changed. According to a California DMV filing first reported by writer Mark Harris, one of Google's self-driving Lexus SUVs drove into the side of a bus at low speed. 
 
 Here's the full description of the incident from the report: 
 
 A Google Lexus-model autonomous vehicle ("Google AV") was traveling in autonomous mode eastbound on El Camino Real in Mountain View in the far right-hand lane approaching the Castro St. intersection. As the Google AV approached the intersection, it signaled its intent to make a right turn on red onto Castro St. The Google AV then moved to the right-hand side of the lane to pass traffic in the same lane that was stopped at the intersection and proceeding straight. However, the Google AV had to come to a stop and go around sandbags positioned around a storm drain that were blocking its path. When the light turned green, traffic in the lane continued past the Google AV. After a few cars had passed, the Google AV began to proceed back into the center of the lane to pass the sand bags. A public transit bus was approaching from behind. The Google AV test driver saw the bus approaching in the left side mirror but believed the bus would stop or slow to allow the Google AV to continue. Approximately three seconds later, as the Google AV was reentering the center of the lane it made contact with the side of the bus. The Google AV was operating in autonomous mode and traveling at less than 2 mph, and the bus was travelling at about 15 mph at the time of contact. The Google AV sustained body damage to the left front fender, the left front wheel and one of its driver’s -side sensors. There were no injuries reported at the scene. 
 
 The Verge has obtained an excerpt from Google's next monthly self-driving report, which is due to be released tomorrow. In it, Google says the car assumed that the bus would yield when it attempted to merge back into traffic: 
 
 Our self-driving cars spend a lot of time on El Camino Real, a wide boulevard of three lanes in each direction that runs through Google’s hometown of Mountain View and up the peninsula along San Francisco Bay. With hundreds of sets of traffic lights and hundreds more intersections, this busy and historic artery has helped us learn a lot over the years. And on Valentine’s Day we ran into a tricky set of circumstances on El Camino that’s helped us improve an important skill for navigating similar roads. El Camino has quite a few right-hand lanes wide enough to allow two lines of traffic. Most of the time it makes sense to drive in the middle of a lane. But when you’re teeing up a right-hand turn in a lane wide enough to handle two streams of traffic, annoyed traffic stacks up behind you. So several weeks ago we began giving the self-driving car the capabilities it needs to do what human drivers do: hug the rightmost side of the lane. This is the social norm because a turning vehicle often has to pause and wait for pedestrians; hugging the curb allows other drivers to continue on their way by passing on the left. It’s vital for us to develop advanced skills that respect not just the letter of the traffic code but the spirit of the road. On February 14, our vehicle was driving autonomously and had pulled toward the right-hand curb to prepare for a right turn. It then detected sandbags near a storm drain blocking its path, so it needed to come to a stop. After waiting for some other vehicles to pass, our vehicle, still in autonomous mode, began angling back toward the center of the lane at around 2 mph – and made contact with the side of a passing bus traveling at 15 mph. Our car had detected the approaching bus, but predicted that it would yield to us because we were ahead of it. (You can read the details below in the report we submitted to the CA DMV.) Our test driver, who had been watching the bus in the mirror, also expected the bus to slow or stop. And we can imagine the bus driver assumed we were going to stay put. Unfortunately, all these assumptions led us to the same spot in the lane at the same time. This type of misunderstanding happens between human drivers on the road every day. This is a classic example of the negotiation that’s a normal part of driving – we’re all trying to predict each other’s movements. In this case, we clearly bear some responsibility, because if our car hadn’t moved there wouldn’t have been a collision. That said, our test driver believed the bus was going to slow or stop to allow us to merge into the traffic, and that there would be sufficient space to do that. We’ve now reviewed this incident (and thousands of variations on it) in our simulator in detail and made refinements to our software. From now on, our cars will more deeply understand that buses (and other large vehicles) are less likely to yield to us than other types of vehicles, and we hope to handle situations like this more gracefully in the future. 
 
 And in fairness, unless every single car on the road is autonomous, Google is right: there is some degree of negotiation involved, and false assumptions in those negotiations are where the crashes can happen. We're many, many years away from a road free of human drivers, and until then, self-driving cars are occasionally going to hit things. It just so happens that this is the first time the crash was directly attributable to the car, not another driver on the road, and it all comes back to a bit of (surprisingly human) bad judgment. 
 
 Update Feb 29th 2016, 2:39PM ET: Added in an excerpt from Google's February self-driving report, which details the crash.
– After six years and millions of miles of driving, one of Google's self-driving cars has become a self-crashing car. The company has admitted that a self-driving Lexus SUV bears some responsibility for a Feb. 14 crash in Mountain View, Calif., the Verge reports. But no people—or robots—were seriously harmed: According to the DMV's accident report, the vehicle encountered sandbags placed around a storm drain when it approached an intersection. When it moved one lane over, it hit the side of a bus that it had incorrectly assumed would yield. The car was only traveling around 2mph at the time of the collision, which damaged its left front fender, the left front wheel, and a sensor. The 15 bus passengers were transferred to another vehicle. 'We clearly bear some responsibility, because if our car hadn't moved, there wouldn't have been a collision," Google said in a statement. "That said, our test driver believed the bus was going to slow or stop to allow us to merge into the traffic, and that there would be sufficient space to do that." There have been other crashes involving Google cars, but this is the first time the company hasn't blamed them on human drivers, Reuters reports. The company says it has learned from the experience and adjusted its software so that its vehicles fully understand that buses are "less likely to yield to us than other types of vehicles, and we hope to handle situations like this more gracefully in the future."